Loading a two-dimensional grid with active devices offers a means of combining the power of solid-state oscillators in the microwave and millimeter-wave range. The grid structure allows a large number of negative resistance devices to be combined. In this approach, the combining is done in free space, and the active devices do not require an external locking signal. The loaded grid is a planar structure amenable to monolithic integration. Measurements on a 25-MESFET grid at 9.7 GHz show power-combining and frequency-locking without an external locking signal, with an ERP of 37W. Experimental far-field patterns agree with theoretical results obtained using reciprocity.
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In this paper a feedback model of second harmonic oscillators is developed. By using describing functions of nonlinearity of active devices, the performances of second harmonic oscillators are studied. Frequency dependence of I-V characteristics of active element are taken into account. The ratio of maximum output power of second harmonic to fundamental is given. The maximum harmonic locking bandwidth of injected harmonic oscillator is derived. The theoretical prediction is compared with experimental results.
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The quantum well injection transit time (QWITT) diode is a transit time device that couples a heterojunction barrier structure as an injector with a depleted epitaxial drift region, as shown in Figure 1. The device, which was originally proposed by Kesan et al. [1], is a promising solid state source with potential for operation at the higher millimeter wave frequencies. Both large and small signal analyses of the device have shown that the specific negative resistance due to transit time effects from the drift region are on the order of, or are significantly greater than, the intrinsic negative differential negative resistance of the quantum well double barrier diode. This paper presents results of a large signal simulation which uses a full set of semiconductor time dependent transport equations, and solves self-consistently for the electric field as well as for the electron and hole populations throughout the device.
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Circuits in which oscillators are integrated with antennas to form quasi-optical sources have applications in phased array radar (1), quasi-optical local oscillators (2), and a variety of obstruction detection and process control applications (3). In this paper we describe a low-cost planar oscillator circuit in which 2 FETs are coupled by microstrip rampart line antennas and operate in a push-pull power combining configuration. Prototype circuits have been constructed which operate at X-band; the same principle may be applied at higher frequencies.
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Basically, frequency division is possible by synchronizing a harmonic mode oscillator at its harmonic frequency fH while coupling out the fundamental frequency fF. However, the very high virtually external 0-factor (>1000 c.o. [1]) of standard type harmonic mode oscillators limits the bandwidth of operation to only a few hundred MHz at moderate input power levels.
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Metal-Insulator-Semiconductor FETs (MISFETs) when fabricated from GalnAs semiconductor material offer significant performance improvement at mm-wave frequencies. Higher electron velocity, power-added efficiency, device stability, transconductance and resistance to ionizing radiation are the outstanding features of these devices. Significant improvements in gain-bandwidth product, AM/PM performance, and third-order intermodulation distortion make GalnAs devices attractive for communication and radar equipment.
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Attempts are recommencing, after a ten year dormancy, to use lightwaves in as sophisticated manner as that in which radio waves are used. Technologies previously developed for radio wave systems are now being transferred to high speed/large capacity advanced lightwave communications. This paper reviews key technologies for advanced lightwave communications, especially optical heterodyne/homodyne detection and optical FDM ( frequency division multiplexing). 1.INTRODUCTION Almost one hundred years have passed since Marconi invented radio communication, and about thirty years have passed since the invention of the laser. Present practical fiber optic communication systems convey information by changing optical "power". In other words, present optical communications are at the level of spark discharge radio communications in the 1890'. With the recent development of coherent light sources, more sophisticated communication technologies which utilize the very large bandwidth potential of optical carriers are becoming feasible (1)-(4). Advanced lightwave technologies using coherent light sources have potential for constructing large capacity communication systems, breaking through the present barrier of incoherent light communication performance. There are two ways to improve transmission capacity : (1) high speed transmission - time division multiplexing, and (2) multi-channel optical transmission - optical frequency division multiplexing. A key technology in high-speed transmission is optical heterodyne detection., and a key technology in optical multiplexing transmission is optical frequency division multiplexing ( optical FDM). This paper describes the present state and perspectives of these advanced lightwave technologies. 2.HETRODYNE DETECTION TECHNOLOGY A block diagram of a communication system using heterodyne detection is shown in Fig.1. Figure 2 shows theoretical estimations of high speed transmission system repeater spans. The combination of FSK or PSK modulation and optical heterodyne detection permits significantly improved sensitivity , improved by more than 15dB over conventional direct detection.
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High-speed or wide-band light modulators are described. It is shown that high-performance microwave light modulators are realized with the optical guided-wave structure and traveling-wave type operation. The integration of high-performance modulators is also discussed. Other topics include the efficient light modulation at millimeter-wave frequencies and the generation of extremely broad optical sideband (0.64 THz) by a microwave light modulator.
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The bandwidths of semiconductor lasers, modulators and photodetectors have dramatically increased recently, making it possible to directly modulate light with signals whose frequencies extend from dc to millimeter wave frequencies. Furthermore, the low attenuation of optical fiber and modulation-frequency-independent nature of the attenuation makes lightwave transmission of broadband microwave signals attractive. Recent advances in generating subpicosecond optical pulses at microwave frequencies using semiconductor lasers has made it possible to generate combs of frequencies extending through the entire microwave and millimeter wave spectrum. With present and next generation photodetectors to detect these optical signals, many applications of optoelectronic devices to spectroscopy, analog and digital transmission, electro-optic sampling, and high speed electronics and optical computing have become important.
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This paper is concerned with recent developments related to optically controlled phased array antennas operating in the millimeter wave range. The antenna consists of three main elements: the central processing unit (CPU), the fiberoptic (FO) distribution system with optical signal processing capability, and the planar array. The antenna array is composed of a large number of distributed and independently powered transmit/receive (T/R) modules fabricated by monolithic microwave integrated circuit (MMIC) techniques. The function of the fiber optic distribution system is to distribute the carrier reference signals for the frequency synchronization of the T/R modules, to transmit the appropriate control signals for beam forming, and to route the information and data signals.
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This paper proposes and analyzes a GaAs traveling-wave optical modulator which uses a modulated coplanar strip electrode with periodic cross-tie overlay. This slow-wave structure can be designed to satisfy phase velocity and impedance matching conditions simultaneously. The dominant conductor loss in the slow-wave structure is reduced using the modulated coplanar strip electrode. The calculated modulation bandwidth is much wider than those of conventional electrode structures which are limited by phase velocity mismatch.
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The complexity usually associated with scanning arrays at millimeter wavelengths produces fabrication difficulties, so that alternative methods are needed that employ simpler structures. This paper describes such an alternative scanning approach, and presents a group of new and simpler radiating structures suitable for millimeter-wave applications.
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Recent developments in microwave/millimeter-wave solid-state devices and integrated circuits have made it possible to integrate the active sources directly with planar antennas. The circuits have advantages of low cost, small size and monolithic implementation. This paper summarizes the recent results, potential applications and future trends of active antenna elements.
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We are developing antenna arrays as detectors for millimeter-wave imaging. The antenna is a resonant dipole [1] with a director in a dielectric lens. Our goal is to measure the plasma density of the TSUKUBA GAMMA-10 plasma machine.
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An Omni-directional periodic dielectric rod antenna operating in TMon mode is investigated. As an eigenvalue problem, the structure is analyzed theoretically with mode matching technique. The radiation characteristics are calculated for different parameters with a particular attention directed to the Brewster angle effect on the performaces of the antenna.
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Two-dimensional horn-antenna arrays are monolithic, high-efficiency imaging detectors of millimeter-wave radiation. In this configuration, a dipole antenna is suspended in a pyramidal horn on a 1-μm silicon oxynitride membrane. This approach leaves room on the wafer for low-frequency lines and processing electronics. Antenna pattern measurements on single elements agree well with theory, exhibiting 3-dB beamwidths of 54° and 62° for the E and H-planes respectively. Horn aperture efficiencies of 44 ± 4% have been measured at 93 GHz. Loss processes include impedance mismatch loss, due to impedance mismatch between the antenna and the detector, resistive loss in the horn sidewalls, cross-polarization, intrinsic pattern loss, and horn-to-horn coupling loss. A system efficiency of 24% has been measured for a lens-coupled array.
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Electrically thick layered substrates using the resonant structures discussed in [2-4] offer the advantage of providing simple and efficient support for millimeter wave printed circuit antennas. They can also produce desirable beam patterns through the proper choice of dielectrics. There has been theoretical study of these layered structures [2-4], but experimental investigation has been limited. Also, the primary focus has been on the use of dipole antennas with these structures, while slot antennas have received little attention. Here we give results for efficiency calculations for both slots and dipoles, and experimental pattern measurements for slots on layered substrates which show that they can produce desirable beam patterns with high front-to-back ratio. We find good agreement between theory and lOGHz modeling experiments.
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A technical review and appraisal of ongoing basic research in vacuum and plasma mm-wave sources sponsored by the Air Force Office of Scientific Research (AFOSR) will be presented. In all, the work of more than a dozen leading scientific laboratories will be discussed. Emphasis will be placed on individual project goals, recent results, and important technical issues.
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A review of recent progress at the University of Maryland's Laboratory for Plasma Research (LPR) on the development of millimeter-wave free electron lasers (FELs) using short period electromagnet planar wigglers and low voltage (Vbeam ≈ 500kV) sheet electron beams will be given.
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We present the test results of a novel microwiggler structure [1] for free-electron lasers, in which, each 2.4 mm period consists of two channels of miniature electro magnets energized by current with opposite polarities. The magnetic field in each half-period is independently controllable and the tunability is demonstrated experimentally, which may provide means for reducing random field errors; for field tapering; for optical klystron configurations; and for electron beam injection.
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An analytical fluid theory is developed for a circular free electron laser, including the effect of the space charge wave. The dispersion relation of the FEL radiation and the space charge wave is analytically obtained. It is found that the space charge wave gives strong effect on the performance of a circular FEL.
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The stability of sidebands in a free electron laser is determined in the regime in which the three-dimensional structure of the modes is important. It is found that the growth rate of the sidebands in the presence of a fundamental mode which is weakly guided by the beam is reduced. The indications are that for some parameters the spatial growth rate of the sidebands can be made less than that of the fundamental.
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An FEL amplifier with a helical quadrupole wiggler is investigated analytically and numerically. A 3-D simulation code is utilized to examine the nonlinear evolution of circular waveguide modes as well as the characteristics of relativistic particle motion, which illustrate a strong focussing effect. The simulation predicts a 0.55 dB/cm gain, 2% efficiency, and 8% bandwidth for the optimum TE21 mode at 300 GHz for an untapered wiggler. Mode competition for an over-moded waveguide and a nonlinear wiggler taper for efficiency enhancement are examined for a linear dipole wiggler in a rectangular guide. It is found that the maximum TEoi mode efficiency is 53% at 280 GHz and that the TM21 mode power can be as high as 28% in the uniform wiggler region.
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In this research the feasibility of developing high efficiency mm-wave multipliers in the frequency range of 130-350 GHz has been studied. A frequency quadrupler for 140 GHz, frequency doublers for 183 GHz and 230 GHz and a frequency tripler for 345 GHz have been analyzed and optimized. The development of high efficiency frequency multipliers is especially important for the spaceborne mm-wave and submm-wave heterodyne receivers used for radio astronomy and remote sensing of the atmosphere.
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A small-signal and large-signal analysis of a traveling wave structure implemented by periodically loading a parallel-plate waveguide with QWITT diodes is presented. The analysis starts with a self-consistent, large-signal model for the diode. The diode model is then coupled to a model for the waveguide circuit and solved using the harmonic balance technique. The output power as a function of frequency for three harmonics for a QWITT oscillator is determined. Our results emphasize the importance of obtaining the ac voltage modulation self-consistently from the circuit when calculating the output power obtained from a QWITT oscillator. The oscillation frequency of the multiple-diode circuit is determined primarily by the periodicity of the structure. The physical dimensions of the waveguide facilitate monolithic fabrication of the oscillator circuit.
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This paper presents a generalized field analysis method for calculating the external circuit impedances looking outside from the active devices of some millimeter wave oscillators. For a simple oscillator model with a radial disc and a diode existing in a rectangular waveguide, the numerical results are in agreement with the experimental data. Impedance characteristics for several different oscillator configruations are given, and sane useful conclusions for oscillator design are derived.
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Diocotron stability properties in a relativistic electron flow generated inside high power magnetrons are investigated within the framework of a linearized macroscopic cold fluid model. A massless guiding-center approximation has been made in this theoretical calculation to be analytically tractable. Closed algebraic dispersion relations obtained in this article are fully relativistic and fully electro-magnetic. Influence of the anode resonator effects are also fully incorporated. Numerical investigation of the dispersion relation is carried out for a broad range of system parameters and results will be presented.
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This paper describes a power combining system using two push-pull power amplifiers. Power amplifiers using two different type phase inverter were proposed and tested at 5-GHz band. Bandwidth of these power combining systems were 1.65 GHz and 1.8 GHz, respectively, and either of their output power were 14.5 W.
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A new cavity for millimeter and submillimeter wave solid-state oscillators is demonstrated. The resonator consists of a Fabry-Perot resonator with a grooved mirror. It has a capability for power com-bining. Experimental results from X-band models of the resonator are presented. Frequency-locking and power-combining with six Gunn diodes are demonstrated.
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The diocotron instability for sheared, relativistic electron flow in a planar diode geometry with major fields Ex(x), Bz(x), and Vv(x) has been studied numerically by using a two-dithensional electromagnetic relativistic particle-in-cell code. The growth rate and real oscillation frequency are obtained and compared to the analytical results for a tenuous electron flow.
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Stable and low noise operation of a Josephson parametric amplifier has been obtained at 9GHz. Best performance was acheived in the externally pumped modes giving a double side-band noise temperature of 3±4K, a gain of 13B, and an instantaneous bandwidth of 310MHz. An operation mode that uses the internally generated Josephson oscillation as the pump source gave higher noise (-50K) due to the broad width of the pump.
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Recent progress on the application of picosecond optoelectronics to microwave and millimeter-wave technology will be reviewed. Generation, control and characterization of pulsed and continuous-wave millimeter-waves will be discussed. A novel network analyzing technique for a 30 GHz monolithic millimeter-wave integrated circuits based on picosecond pulses has been demonstrated.
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The experimental performance of an a optically-controlled coplanar waveguide phase-shifter fabricated on a heterojunction substrate containing a thick GaAs layer buried between two A1GaAs layers is presented. The measured performance shows that relative phase-shifts of 1000 can be obtained even for optical input powers in the tW range. Introduction Studies of coplanar waveguides (CPW) on semiconductor multi-layered substrates have shown, that within that the range of resistivities covered by most semiconductor substrates and the frequency spectrum of interest for microwave and millimeter wave applications, a slow wave (SW) mode of propagation can exist [1]. A typical structure consist of a thin lossless layer immediately below the CPW, followed by a thicker lossy layer and a third lossless layer. The slow wave factor (SWF), which is the ratio of the effective guide wavelength to the free space wavelength, is a measure of the change of the effective refractive index of the substrate. The magnitude of the SWF is a function of both the resistivity of the buried lossy layer and the thickness of the first layer. Because of the dependence of the SWF on the properties of the underlying substrate, a CPW on a multi-layered substrate can be used as a variable phase-shifter if either the conductivity or layer thicknesses can be actively controlled. At the 10th IR & MMW conference [2], a method of optically controlling a coplanar-waveguide (CPW) phase-shifter was proposed. By the appropriate selection of semiconductor heterojunction substrate materials (A10.4Ga0.6As / GaAs / Al0AGa0.6As) and the corresponding selection of an illuminating source of the correct wavelength (wavelengths longer than 600 nm, but shorter than 860 nm), the conductivity of the buried GaAs layer can be controlled by the intensity of the optical source. The phase shift is then controlled directly by varying the intensity of the illuminator. At last year's IR & MMW conference [3] preliminary measurements of a prototype device were reported. The results indicated that relative phase shift can be obtained even at relatively low levels of intensity. Recently Kwon, et al [4] showed that the slow-wave mode propagating on the CPW can be modeled by a quasi-TEM circuit model. Using this approach we have developed an equivalent circuit model for an ideal optically controlled CPW phase-shifter [5]. The analysis showed that when a large percent of the total "equivalent thickness" of the substrate is lossy, large relative phase-shifts can be obtained. By conformal mapping this translates into a thick second lossy layer for a typical structure. To test this prediction, a device was fabricated on a substrate with a thick GaAs (711m) layer.
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Recent optical switching devices are using combinations of very short laser pulses, photoconductors, and strip lines. Since laser pulses have giga-hertz-bandwidth, signal transmission properties of such strip lines in a wide range of frequencies are decisively important. This paper describes the structural control of the dispersion characteristics of microstrip lines by adding ground conductors on both sides of the strip conductor. Some numerical data are shown.
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The inverted slot line is proposed with the pur-pose of applying to optical modulators operating at millimeter-wavelengths. Velocity of millimeter-waves can be matched to that of optical waves in LiNbO3 material by simply adjusting the spacing between th6 slotted surface and the ground plane.
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An optical technique using picosecond pulses has been developed to characterize the magnitude and phase of the frequency response of a gallium arsenide (GaAs) monolithic integrated circuit in the millimeter-wave frequency range. The results of the complex S-parameters of an amplifier obtained using this technique were compared with those obtained using the network analyzer method.
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An optical fiber has been used to illuminate a HEMT. This causes modifications of the static and dynamic characterics of this component. A home made sophisticated software extracts the elements of the classical electric scheme of microwave FETs from their "S" matrix. The effect of the light on the major elements are decribed and compared with the results for MESFETs.
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We developed a microwave oscillator based on a series array of 100 long Josephson tunnel junctions coherently working in the fluxon resonating mode. This prototype has satisfied all the requirements (output power, frequency, signal stability and purity) for local oscillator in integrated superconducting millimeter receivers.
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A balloon-borne far-infrared telescope has been designed and built to observe the infrared emission from the Cygnus region in the galactic plane between 120 μm and 300 μm wavelength. The system performance, objects as well as results of the first flight in September 1988 will be discussed.
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This report is about a mechanically tunable solid state source with a varactor quintupler in waveguide technique. Its main purpose was to provide output power at 490 GHz for use in a radioastronomy receiver (1). The device has been tested between 470 and 550GHz. Results are presented as increase in rectified current in a dc-biased Schottky-Detektor.
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We describe an induction-linac based free-electron laser amplifier that is presently under construction at the Lawrence Livermore National Laboratory. It is designed to produce up to 2 MW of average power at a frequency of 250 GHz for plasma heating experiments in the Microwave Tokamak Experiment. In addition, we shall describe a FEL amplifier design for plasma heating of advanced tokamak fusion devices. This system is designed to produce average power levels of about 10 MW at frequencies ranging from 280 to 560 GHz.
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After a brief review of the basic free-electron laser (FEL) physics, we will discuss the following topics : efficiency optimization of a millimeter-wave FEL, optical guiding experiments in a microwave FEL and pulse shaping and compression in a FEL amplifier.
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The effect of multimode interaction on the efficiency of a low gain FEL oscillator fed by a continuous beam is investigated. Calculations that enable one to design a device in such a way that it will operate at a single frequency with maximum efficiency will he presented. The model we consider is the one dimensional, low gain oscillator.' Due to low gain, the radiation field in the resonator can he expressed as a superposition of empty cavity modes whose amplitudes and phases change slowly in time (compared with the transit time of the electrons through the interaction region) due to their interaction with the beam. The field at any point will he nearly periodic in time with a period equal to the round trip travel time of radiation in the cavity, which we assume to he much smaller than the time scale over which the amplitudes change. We may then numerically integrate the following set of equations.
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With the help of the unitary S matrix in the linear recoil approximation, the study of the spontaneous and the stimulated emission and absorption of higher harmonics in the uniform magnetic field free-electron laser is being pursued. The stimulated emission of single-mode photons, being due to just one harmonic, can be tuned to cover a rather limited frequency range, particularly the far-infrared/microwave spectral region. The spontaneous emission, because it is due to all the harmonics, covers a wide spectral region; consequently, at least in principle, it should be able to stimulate at least some higher harmonic radiation. Here, for theoretical and practical reasons, we limit our study largely to harmonics whose emission (absorption) occurs at angles that are "slightly" different from zero with respect to the uniform magnetic field.
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We report high power emission (18 MW) at a wavelength of λ = 640 μm and a bandwidth ΔAλ/λ< 0.04 from a superradiant free electron laser (FEL) excited by a 2MeV, 1 kA electron beam. Comparison of the experiment with a nonlinear simulation yields good agreement. Theoretical extrapolation to a tapered wiggler experiment shows that power levels of 140 MW could be achieved with an efficiency of 7%.
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In terms of Bogoliubov's nonlinear oscillation thoery, the first five betatron-synchrotron resonances of Ω=(p/q)2kβ=1/2,1,3/2,1/3,2/3 which may occur during laser satulation establishing process have been generally examined. Contrast to previous studies it is found that the most dangerous resonance does not take place in the vicinity of Ω=2kβ but in that of Ω=kβ. The width of region of Ω=kβ is proportional to ε with ε∝ (k2w/kβ)*emittance, the passing 'time' over the region due to he laser field being amplified is only one pass over the undulator at most and depends on the gain, and the increment of synchrotron amplitude in passing time is proportional to ε. In summary we conclude that the betatron-synchrotron resonances does not have any significant effect for detrapping off-axis electrons in a practical case.
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We have developed a first Raman FEL in China [1]. A recent experiment for improving the efficiency is reported. The wiggler length has been enlarged from 79 cm to 119 cm, the efficiency of 3.7% was obtained.
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A rugged, compact, battery-powered millimeterwave (mm-wave) radar has been developed by using a prototype orbitron maser as the source. The orbitron maser was found suitable for such an application since it is high power, wideband (thus multi-channel) and frequency tunable. The radiation emanating directly from the tube was fairly uniform and the divergence angle (100) was diffraction-limited. The orbitron pulse had a fast risetime (10Ons), short pulsewidth (500ns) and no spurious oscillations. The orbitron output power was 6.7W minimum (possibly ~6.7kW due to the detector saturation and 400kW input power) at the V-band (50-75GHz). The power levels were similar at lower bands and constant up to 10Hz of repetition frequency. An innovative DC-DC converter was used to amplify 24V of battery potential up to 1000 times. The orbitron maser was characterized by simultaneous measurements of the applied voltage, discharge current (thus input-power and plasma-resistance), luminousity and wave signal. A linear scaling law was found for the mm-wave power to increase with the discharge current. Output power with hydrogen was twice to that observed with air or nitrogen working gases.
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In designing broadcast satellite transponders, it is required for the filters handling high-power RF signals to have not only low-loss characteristics but also good thermal stability. In order to realize such filter performance, we proposed a 6-pole canonical TE113 dual-mode filter which is formed of silver-plated Super Invar cavities with copper iris plates. The insertion loss and thermal stability of the experimental filter were 0.3dB and 1.5ppm/C, respectively. Also, no significant deteriora-tion on the filter performance was observed even at the RF input power of around 400W. AS a result, it was found that this type of filter was most suitable for the high-power satellite transponders in view of insertion loss, thermal design, volume and weight.
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A technique for recognizing real targets by millimeter wave (MMW) radar at 35 GHz and 94 GHz is presented. The recognition is performed by a model based technique in which real targets are represented by their high range resolution (HRR) profiles in a hierarchical fashion. The unknown signal is classified by a model matching method and a coarse-fine searching technique. The advantages of this model based method are in low storage capacity, fast processing time and high recognition performance. Moreover this technique is very easily modifiable to incorporate infrared sensor processing. We will present the results of the several experiments that we have conducted.
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A 26 to 40 GHz block converter for receiver frequency extension will be described. The converter has a 15 dB NF, 10 dB, conversion gain, ≥.5,0 d spurious-free dynamic range, built in BITE, 44 GHz L.O. and measures 3x3x1 inches. A 33 to 36 GHz up/down converter for an airborne jammer pod will also be described.
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There are many applications of remote sensing in the frequency range near 200 GHz. The determination of the role of man-made chlorine compounds in the destruction of the ozone layer observed through the emission from C/O near 200 GHz is one example. Another example is the observation of CO at 230 GHz as a tracer of matter in the interstellar medium. Heterodyne receivers are the instrument of choice to perform these observations due to their high sensitivity and spectral resolving power. The nonlinear tunneling currents in a superconductor-insulator-superconductor (SIS) tunnel junction have been shown both theoretically and experimentally[1] to provide the lowest noise mixing element at millimeter wavelengths in these receivers. When properly optimized, an SIS mixer displays the important properties of conversion efficiency greater than unity and noise temperature approaching the quantum limit.
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An optically-controlled microstrip line coupler is analysed based on Galerkin's method in the spectral domain. The scattering parameters of ports are derived as a function of plasma density in semiconductor substrate. Results are confirmed by experiments in the frequency band from 1 to 15 GHz.
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We report the results of the optical generation of microwave signals superimposed as a modulation on an optical carrier by means of laser heterodyning. The modulated optical carrier can be easily distributed with fiber-optic cables. This approach offers microwave distribution advantages in size, weight, cost, and frequency diversity, which are desirable in improtant applications such as phased antenna control.
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The 10 gm CO2 laser, submillimeter-wave FELs, and millimeter-wave gyrotrons are all being proposed for collective Thomson scattering alpha-particle diagnostics. We will assess the relative advantages and disadvantages with wavelength scaling in the 5 mm to 10 μm range for this diagnostic.
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A Thomson scattering diagnostic for measuring the alpha particle velocity distribution is described. Calculations of scattering are made for a CIT type plasma using available CO2 laser and heterodyne technology. Tests of a long pulse CO2 laser, multichannel heterodyne detector, and an absorption cell for stray laser radiation are presented.
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Heating of plasma electrons by high power millimeter wave fields at the electron cyclotron harmonic resonance is studied. A mirror magnetic field is modelled for investigating the local trapping of electrons. Then, the suprathermal electrons generated by the ECRH of trapped electrons is analyzed. It is generally believed that these hot electrons can be used to produce the average minimum B field configuration for stabilizing the interchange mode.
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The properties of highly oversized tubular HE11 waveguide (circumferentially corrugated or dielectrically lined metal guide) and of quasi-optical Gaussian beam waveguide (using focusing metallic mirrors) are reviewed and compared in order to extract the specific advantages and disadvantages of these two approaches for use in low-loss megawatt CW millimeter-wave transmission systems. Manufacturing imperfections may limit the application of the convenient HE11 waveguide to the 1 MW / 100 to 140 GHz range. Quasi-optical transmission is ideal for multi-megawatt millimeter- and submillimeter-wave systems using beam combination. Depending on the power and frequency requirements and on the accessibility constrains, combined systems may be realized.
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A 30 meter long circular corrugated waveguide run (i.d.=6.35 cm) with a corrugation period and depth of 250μ has been fabricated. It is designed for low loss (<0.01 dB/m) multimode operation over the frequency range of 75-575 GHz. It will be installed on TFTR (Tokamak Fusion Test Reactor) for use in electron cyclotron emission measurements. Results will be compared to those obtained using conventional tall rectangular C-band waveguide.
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A system for launching 53.2-GHz electron cyclotron heating (ECH) power is being installed on the Advanced Toroidal Facility (ATF) fusion experiment at Oak Ridge National Laboratory. The launcher provides a narrow linearly polarized beam. The plane of polarization is easily rotated. Measurements indicate that the launcher will have a -20 dB beam width of 15 cm at the plasma center and polarization purity of >97%. The ATF (1) requires 53.2-GHz microwave power for ECH plasma ionization and heating; this power is generated by a 200-kW cw gyrotron. Theoretical ray tracing studies have shown almost complete first-pass power absorption is possible if the power is within the saddle point in the proper polarization (2). Therefore, a narrow-beam-width launcher with adjustable polarization is being developed. In ATF the confining magnetic field can operate continuously at 1 T or in long pulses at 2 T. Either second harmonic or fundamental ECH absorption occurs, depending on the field strength, and it is of interest to operate experiments using both values. With perpendicular propagation and low-field-side launch, the ECH power must be in the extraordinary mode (X-mode, Erf perpendicular to Bo) for second harmonic (co = 2 wee) or in the ordinary mode (0-mode, Enr parallel to Bo) for fundamental (o) = c),) operation. The magnetic field in ATF is formed primarily by helical windings, which produce a shear in the plane of the field along a radial chord. This shear may cause polarization rotation of the ECH wave as it travels through the outer plasma regions because of the unequal 0- and X-mode phase velocities at higher plasma density (similar to Faraday rotation). The ECH resonance zone is a 10-cm-wide saddle point near the plasma center.
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Very short, broad bandwidth designs will be discussed for varying-radius mode transducers for TE02-TE01 and TE03-TE02 mode conversion in a 2.779 cm diameter circular waveguide at 60 and 140 GHz and for TE15, 2-TE15, 1 mode conversion in 2.54 cm diameter waveguide at 14'0 GHz.
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The far-field radiation patterns from three different circular waveguide antennas are measured with an antenna pattern-mapping system. The radiating ends of the waveguide antennas are each cut at a specific angle relative to the center axis of the waveguide, forming the waveguide launcher component of a Vlasov-type mode convertor. This paper addresses the radiation patterns launched from the waveguide antennas as the first step in the design of a Vlasov-type mode convertor that will function at high power levels in the X-band frequency range (8 to 12 GHz).
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A quasi-optical converter for converting rotating whispering gallery modes into a linearly polarized quasi-Gaussian beam was designed and experimentally tested. The shapes of the launcher and the reflectors were optimized in order to increase the efficiency.
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Plans for Electron Cyclotron Resonant Heating in the Compact Ignition Tokamak call for at least 10 MW at fields from 7T to 10T with extension to 40 MW possible. 1 MW CW Gyrotron sources for fundamental heating are currently in the design phase. The transmission system must accomodate these high powers in addition to the constraints of small space and access in a tritium environment. Quasi-optical and corrugated guide systems are under consideration, as well as hybrid designs. A preliminary design is presented, and options for alternatives are discussed.
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Preliminary results for an experimental and theoretical investigation of TEON mode Vlasov launchers which might be used in conjunction with some gyrotrons will be discussed. We will present experimental radiation patterns taken directly from the half-cylinder baffle and also from the parabolic-cylinder reflector that it feeds. Variations of the half-cylinder baffle and orientation position of the parabolic reflector will be considered.
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Operation of a ubitron/FEL amplifier is reported. The experiment has been operated using the fundamental wiggler harmonic interaction with the TE11 circular waveguide mode. Small signal gains as high as 12dB have been observed at a voltage 15% below design level with a minimum instantaneous bandwidth exceeding 25%. A gain per free-space wavelength approaching 0.9dB/λ has been achieved. Experimental results are compared with small signal calculations and future plans are discussed.
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The Planar Orotron has traditionally consisted of a uniform, rectangular metal grating opposed by a planar conductor (Fig. la)Unbounded at the sides, this open resonator supports travelling waves with frequencies which are determined by the grating dimensions. The dispersion and gain characteristics for this device have been documented theoretically and experimentally in the low beam voltage (5 - 20 kV) regime,1 where powers of up to 2 kW and efficiencies of a few percent at 35 GHz have been recorded. In the frequency range of 150 to 175 GHz , output powers are typically less than 1 W, and efficiencies less than 0.5%. Attempts to improve the output power and efficiency by modifying the resonator design are currently underway in the 30-40 GHz range. Among the new designs are the following, which appear in Figures 1 and 2: 1) A uniform grating is opposed by an identical uniform grating, with a symmetric orientation in the resonator. (Fig. lb) 2) A uniform grating is opposed by an identical uniform grating, with an antisymmetric orientation in the resonator. (Fig. lc) 3) The uniform grating is replaced by a grating with a slight taper (< 10%) and opposed by a conducting plane. (Fig. 2a) 4) The tapered grating is opposed by an identical tapered grating with a symmetric orientation in the resonator. (Fig. 2b) The grating and resonator parameters of interest are shown in the Figures. They are the period, l, and the ratios of groove depth to grating period, d/1 , groove width to grating period, s/l , and the ratio of inner resonator height to grating period, (b-d)/l. In Fig. 2, the groove depth, d, and the distance from the base of the slot to the surface of the opposing component, b, are both functions of the axial position, z.
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A fully relativistic theory of axial injection orbitron maser (AXIOM) oscillators has been completed. The theory models the interaction of axially injected electrons in helical trajectories with the fields of a coaxial cavity resonator. The theory treats TE or TM modes with sinusoidal axial field profiles. The power transferred from the electron beam to the cavity fields is calculated in terms of a general distribution function and the cavity parameters. A cold beam distribution function is used to evaluate the theory. The results of the theory are presented in terms of the threshold value of the cavity Q times the electron beam current IBeam required for self-oscillation.
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We have designed, built and tested several steady-state Orbitron MASERs, which have the unique property of having multiple anode wires. We have found that the multiwire structure increased the output power, efficiency, and reduced the heat loading of individual anode wires. We have also experimented with these devices in a pulsed mode and found similar results.
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The modified peniotron oscillator proposed by the authors has been experimentally studied and a fairly high electronic efficiency 50% and 62% of the efficiency by the use of a potential-depressed collector were obtained. This paper describes the operation characteristics of the modified peniotron and point out that the alignment of the respective axes of the tube and the magnetic circuits is very important in a peniotron tube.
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We propose a new configuration of the auto-resonant peniotron oscillator(ARPO) consisting of an oscillator part with a low output power and an amplifier part and report the analytical results of its operational characteristics. The results show that a multi megawatts oscillator tube with an extremely high conversion efficiency should be possible to develop even in the millimetre and the submillimetre wave regions.
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This paper presents a structure for a fundamentally pumped balanced mixer with whisker contacted diodes. The structure suggests compact and unique solutions for placing two connected diodes in an extremely small hybrid T, and for a low loss adjusted waveguide short. At 183 GHz this mixer's noise temperature was under 600 K double-sideband measured at room temperature, a figure achieved until now only with single-ended mixers.
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An accurate monolithic power meter has been developed for millimeter-wave applications. The detector is a large-area Bismuth bolometer, integrated on a fused-Quartz substrate. It simply measures the temperature change caused by the absorption of millimeter-wave radiation. The power meter is easy to fabricate, and can be calibrated using a low-frequency network. The measured responsivity for a 1x1cm bolometer is about 1mV/W, at a bias of 1V. and a video modulation of 100Hz. The noise spectrum exhibits a 1/f rolloff below 1KHz, and is limited by the Johnson noise for higher frequencies. The NEP of the detector is 3x10-6W H z -1/2 at a video modulation of 1 KHz. It is possible to decrease the current NEP by fabricating bolometers with higher responsivities. Possible application areas are absolute power calibration and localized power-density measurements for millimeter and submillimeter wavelengths.
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Millimeterwave detectors have been made of a series-connected array of Josephson junctions. Each junction of the array responds in phase to radiation and therefore the series-connected array as a whole behaves as if it were a single Josephson junction. When the Josephson junctions have a high critical current density, the IF outputs have sharp peaks at the voltages V = 2NΔ/ne where N is the number of the Josephson junctions in series connection and n is an integer. The subharmonic energy gap structures in voltage-current curves of Josephson junctions come from the Andreev-reflection-assisted-tunneling according to the recent Arnold theories.
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A high resolution multichannel far-infrared interferometer has been constructed for the ATF experiment at Oak Ridge. The system consists of a pair of cw 119-pm methanol lasers, optically pumped by separate CO2 lasers. An external Stark-cell modulation scheme is used to stabilize the frequencies of the CO2 lasers. The system is designed to be operated, monitored, and stabilized by a PC computer.
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A one channel FIR polarimeter/interferometer, with HCN laser of 0.337 mm is designed for JIPP T-II U Tokamak, in order to prove the possibility of the inference of current density distribution. The measurement itself is successful, of the distributions of the line density and Faraday rotation angle with the accuracy of 0.1 fringe and 0.1 degree respectively.
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A six-channel HCN laser interferometer system has been developed for the measurement of the electron density profile in the JIPP T-IIU tokamak. The optical configuration is of the Michelson interferometer type, of which reflecting mirrors are directly attached on the wall of the vacuum vessel. This optical configuration enables the density profile measurements by the multichannel laser interferometer with a small optical window.
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A formic acid laser operating at 433 μm and a gyrotron which is step-tunable in the range 75-330 GHz are being used to study density fluctuations in a small tokamak during Alfven wave heating. The scattering systems and recent results will be discussed.
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A dual channel, 119μm wavelength laser system has been constructed for the ATF experiment at Oak Ridge. The pump lasers utilize external Stark cells for locking the CO2 laser to the absorption frequency of the CH3OH lasers. Stark plates have also been attached to the dielectric waveguide resonators of the FIR lasers to affect precise tuning of the 119 μm lasers.
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A formic acid laser has been operated simultaneously on three lines of a cascade sequence by suitable choice of the resonator length, resulting in enhanced power on all three lines. The phenomenon can be used to construct a phase-modulated interferometer. For the output coupler used which exhibits phase anisotropy, simultaneous output on two orthogonally polarized lines of a cascade sequence has also been obtained.
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As a result of steady progress in high power FIR lasers and sensitive, low-noise detection systems, the equipment is now available to measure the ion temperature (Ti) of tokamak plasmas by Thomson scattering from thermal density fluctuations. Using a laser in the far-infrared wavelength range permits scattering angles as large as 90° which results in excellent spatial resolution of the measurement. Heterodyne receivers built around Schottky barrier diode mixers combine high sensitivity with large electrical bandwidth to cover the frequency spread of the scattered radiation. After a first demonstration of feasibility was reported by Woskoboinikow et al (1), recent improvements on our system made it possible for the first time to measure Ti in a single laser shot.
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A dual channel, low noise heterodyne receiver has been constructed for Thomson scattering from alpha particles in a burning plasma experiment. A real time calibration method has been devised which references the integrated system noise to a blackbody source. Two wideband (>1GHz) HgCdTe photovoltaic mixers yield a double sideband system noise equivalent power of less than 1.5 x 10-20 W/Hz.
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A high temperature (T = 500°C) radiation source has been developed for the calibration of electron cyclotron emission measuring system on the JIPP T-IIU tokamak. The source has a heated area of (1)150 mm, and has the same emissivity as that of the microwave absorber Eccosorbe. The grating polychromator has been calibrated using the radiation source developed. The obtained electron temperatures agree with those by Thomson scattering within 10%.
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A Stark-tuned laser operating on the 119 micron line of CH3OH has delivered reasonably high power (several tens of milliwatts at 30 Watts of pump power) while simultaneously exhibiting a doublet splitting of about 10 MHz, which is an order of magnitude larger than the modulation frequencies currently being used in plasma interferometers. Because the resonator design has allowed the attainment of both high power and high doublet splitting, this type of laser would be usable in the type of multi-channel interferometers currently employed on the large-scale plasma devices being used in magnetic fusion research.
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Atmospheric turbulence, which is a readily observed phenomenon at visible wavelengths, also causes fluctuations in intensity and phase at millimeter wavelengths. This paper describes a series of experiments conducted at a site near Flatville, IL which measured these effects at a broad range of MMW frequencies in clear air, rain, fog, and snow. It was found that the maximum rms intensity fluctuations observed were 14% of the mean, while the largest rms angle-of-arrival fluctuations were 36 microradians. Discussions of the experimental arrangement, as well as results obtained in measuring the probability distribution functions of fluctuations, the mutual coherence function, spectral densities, and pertinent atmospheric parameters will be presented.
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A practical, PC-operated atmospheric propagation model (MPM) was developed by ITS that predicts attenuation (dB/km) and delay (ps/km) rates for frequencies between 1 GHz and 1 THz. Input variables are barometric pressure, ambient temperature, relative humidity, hygroscopic aerosol concentration, suspended water or ice droplet concentration, and rain rate. Details of the MPM code are discussed briefly, model predictions are presented, and comparisons with data from propagation experiments studying water vapor and fog effects (50 to 430 GHz) are shown.
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Total atmospheric attenuation under conditions of cloud cover was measured at frequencies of 15 and 35 GHz using the sun as a source. Over 300 sets of data were collected at each frequency. An algorithm for estimating the slant path attenuation under conditions of cloud cover as a function of elevation angle, frequency and surface absolute humidity was derived.
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Communications Research' Laboratory conducted millimeter wave propagation experiemnts at radio window frequencies 1.7, 11.5, 34.5, 50.4, 81.8, 140.7, 245.5 GHz and at 350 THz on shrot terrestrial paths in a suburb of Tokyo during 1979 - 1986. Main results of these experiments will be presented.
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To prepare the future meteorological radiometric satellite missions, we developed a synthetic atmospheric millimeter-waves radiative transfer model including the roughened sea surface emissivity and all-weather conditions. It is to be confronted with measurements of an airborne campaign in window regions of the atmospheric spectrum.
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A model was developed to analyze anisotropic propagation of plane, polarized radiowaves in the mesosphere as influenced by the geomagnetic Zeeman effect displayed by 02 spectral lines positioned in the 60 GHz band. To provide an example here, the 5+ line, centered at the frequency fo = 59.59058 GHz, has been chosen and two cases are discussed: from a location known by latitude and longitude, a radiowave (a) propagates north in an altitude of 75 km at the frequency fo + 1 MHz covering a distance of up to 1000 km; and (b) enters the atmosphere at 100 km altitude, heads in either N, E, S, or W directions, descends to the 75 km level, and then exits again. In the first case, attenuation and polarization state are followed along the path; in the second case, total path attenuations as a function of frequency deviation (f0±MHz), initial polarization, and direction are given.
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The presentation will address the motivation, the strategy and the plan for developing high average power millimeter wave sources under the sponsorship of the Office of Fusion Energy, Department of Energy. Ongoing efforts and expected trends in line with the recent recommendations of a number of review panels will be discussed. The presentation will also highlight some of the fusion experimental applications.
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Varian is in the process of developing gyrotrons capable of generating power levels of 1 MW CW at a frequency of 140 GHz. The first experimental gyrotron in this program has been designed to generate short-pulse power levels of 1 MW and up to 400 kW CW. In recent tests on this gyrotron, a short-pulse power level of 820 kW was obtained at 21% efficiency. While operating at peak power levels of 350-400 kW, the duty factor was raised to 10% (30 pps, 3.33 ms-pulse duration). Power losses in various parts of the tube have been measured and are in agreement with theoretical predictions. Tests at higher average powers, up to the 400 kW CW goal for the tube, are underway. Design efforts aimed at increasing the average power capabilities of the gyrotron up to 1 MW are in progress.
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Design and experimental studies of the 120 GHz, TE03 mode gyrotron of Mitsubishi Electric Corp. are reported. Since the first operation of our 120 GHz, TE03 mode gyrotron (1), our efforts have been aimed at increasing an output power on the second tube. The second tube is a modular type and allows interchange of important parts such as a magnetron injection gun, a cavity and a window. The tube with a nonlaminor gun and a simple tapered cavity (Q=579) has achieved the maximum output power of 167 kW at 120 GHz in the TE03 mode with short pulse. The efforts for increasing pulse width have been also continued. A 150 kW, 10 msec, sealed type of gyrotron was reported at the 5th Annual Conference of the Japan Society of Plasma Science and Nuclear Fusion Research (March, 1988). In this paper, most part is devoted to descriptions of short pulse operation on the second tube. The rest introduces the design of a complex cavity for high power (~200kW) and long pulse (~100ms) gyrotrons.
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A 1 MW, 280 GHz gyrotron oscillator suitable for ECR heating of the Compact Ignition Tokamak (CIT) is presently being designed. The design is based on successful features of our present experiment, which has generated powers up to 765 kW in the TE16,2,1 mode at 148 GHz. In the 280 GHz gyrotron, an 80 kV, 50 A annular beam will interact with a high order whispering gallery mode. Parametric studies indicate that a cavity with a diameter of at least 20A is required to keep wall losses low. Detailed studies of the electron gun and 12 T magnet indicate both are feasible. Initial experiments are planned for late next year.
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The gyroklystron is a potential source for driving advanced accelerators, such as the proposed 300-500 GeV electron-positron collider. Sources with frequencies higher than those commonly used in accelerators (e.g. 2.9 GHz) are desired because higher accelerating gradients can be created, thus reducing the length and cost of the device. Because of the inherent advantages of gyrotrons, such a source is expected to be able to produce significantly higher power at high frequencies than that possible with a linear beam tube. A 10 GHz, 30 MW gyroklystron is being developed at the University of Maryland to demonstrate this potential.[1]
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GYROTRON IV is the latest in a series of tunable gyrotrons designed and constructed at the University of Sydney (1). Like GYROTRON III, it is tuned by raising the field of a 12 T superconducting magnet. One cavity resonance after another is excited. It will provide more than 10 W of cw power over the frequency range 75 to 330 GHz. However, a number of design changes have been made to simplify the construction and improve the quality of the output.
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Coupled planar strip-slot resonators with multiple-layer dielectrics are investigated by the reaction theorem in electromagnetic field theory. A variational formula for the resonant frequency is established, which involves only the electric fields on slots and the electric currents on strips. Two coupled suspended rectangular strip-slot resonators are computed. The numerical results agree well with the experimental data.
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The sole excitation of the HE11 mode along the dielectric rod waveguide up to the 150 GHz band has been studied. Measurements have been done on the guide-wavelengths along the TPX rod waveguide with diameters 3.1, 2.0, 1.5 and 1.0 mm in the 150 GHz band. It has been shown that the TPX rod waveguide with a diameter less than or equal to 1.5 mm can transmit only the HE11 mode in the 150 GHz band.
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An approach for the analysis of waveguides with multiply connected cross section is presented. It is based on a field expansion with respect to the normal modes of the corresponding hollow waveguide with the same outer conductor. This is in particular useful if the outer conductor has a rectangular or circular cross section. The method can be applied to a large number of guiding structures with both touching and non touching inner conductors. This includes e.g. ridged waveguides, finned waveguides, strip lines, and two wire transmission lines. Here the validity of the method is checked by analyzing a coaxial line.
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Using modal analysis, an analytical solution to a circular waveguide discontinuity is obtained which is found in a wide class of coupled cavity travelling wave tubes (CCTWTs). The generalized scattering matrix (GSM) of the junction is obtained for both azimuthally dependent and independent excitations. The convergence of the numerical results is investigated by com-paring the field distributions at both sides of the junction. The (GSM) of the different junctions can be cascaded in order to characterize a single cavity of the TWT structure.
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Cutoff frequencies and field configurations are calculated for both TE and TM modes of the eccentric annular waveguide. In the analysis the cross section of the waveguide is transformed into a coaxial line by conformal mapping. Then TE and TM modes are expanded in terms of the corresponding coaxial modes. Excellent agreement with results obtained by other published methods is achieved. The advantage of the proposed method is its fast convergence.
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There are two types of possible transmission modes in double-groove guides: 1. modes with a concentration of energy in the groove regions, and 2. modes with a concentration of energy in the region between the two grooves. Attention had been concentrated on the first type of modes [1]. This paper gives the theoretical and experimental work on the second type of modes.
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This paper presents an overview of ceramic fabrication techniques and electrical properties of high-Tc superconductors. Fabrication of bulk ceramic and composite, high-Tc superconducting wires and tapes is discussed. Direct-current critical current density data and surface resis-tance data at rf and microwave frequencies are presented for the YBa2Cu307-x and Ba2Sr2CaCu208+y phases.
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A 100-120 GHz open resonator, which has a hemispherical configuration with a plane mirror as the sample itself, is described as a powerful tool for testing mirror samples. Very, weak coupling, which is necessary for the high Q factor, have been achieved without facing with large transmission loss by using a partially-transparent circular aperture which is larger than wavelength. Weak effect on sample surface is sensitively detected by the precise measurement of high quality factor and frequency shift of the open resonator.
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We propose the multi-Cu-02-layer structure model of high Tc superconducting oxides such as Bi2Sr2Ca2Cu3012. The 'hole-Cooper pair' formation and the Bose condensation of the pairs are described by the theory of Huang of MIT. The attractive interaction is due to the antiferromagnetic order of Cu-02 layer. Dependence of Tc on the number of Cu-02 layers is quantitatively analized. Pressure dependence of Tc is also analyzed by use of our model.
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The principle and experimental setup to measure the superconductor surface impedance is described, which characterizes in using an open resonator. The open resonator comprises a couple of parallel conducting plates penetrated perpendicularly by a thin dielectric rod. Along the dielectric rod, the HE11 mode is excited and its resonance between the parallel plates is exploited for finding the surface impedance of the superconducting plate.
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We present a novel technique for the measurement of surface resistivity using whispering gallery modes in an open cylindrical resonator. Preliminary results for copper at 140 GHz and application to high Tc superconductors will be presented.
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We present a fast, wide-spectral range photoconductivity FIR-detector system suitable for application in short, pulsed high magnetic fields.
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We describe the use of cryogenically cooled, extrinsic silicon p+-n-n+ diodes in an unconventional mode of operation as infrared detectors[1], which offer an unusually large dynamic range. The use of these detectors for high dynamic range IR radiometry and IR imaging would require no preamplifiers and could open the way to new means of 3-D processing at or near the focal plane. [2] The detectors perform intensity-to-frequency conversion via circuits with very low power consumption. To our knowledge, these are the only detectors which perform direct IR intensity-to-frequency conversion in the detector itself.
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New IR detectors with twin elements were developed for precision earth sensors of satellites. Two sorts of pyroelectric elements, ceramics and sputtered films, were studied. Each element is mounted on an immersion lens. Minimum random error of attitude measurement is much smaller ( 0.012°) than that ( 0.06°) of our preceding type.
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The noise of GaAs Schottky diode caused by dry etching damage has been studied. The number of traps near the Pt/GaAs interface increases with the damage, and this greatly increases flicker noise. These experimental results can be explained by a theoretical calculation.
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Diode heat sinking and contact resistance optimization play key roles in MOM point contact diode thermal stability for high power laser detection. Such enhancement is realized by further optimization of the hooking parameters of the etched whisker tip.
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Antenna characteristics and noise performance of an improved quasi-optical Schottky-barrier diode mixer have been investigated at 800 GHz. Measurements indicate that system noise can be reduced by about 25% by adding a conical horn structure to a corner cube mixer.
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An small adiabatic demagnetization cooler for an astronomical far infrared detector has been built. Single crystals of manganese ammonium sulphate and chromium potassium alum, were prepared as magnetic substances. The superconducting magnet was indirectly cooled and operated by small current up to 13.3 A, the maximum field being 3.5 T. As a preliminary step, adiabatic demagnetization to zero field was implemented. The lowest temperature obtained was 0.5 K, for 5.0 K initial temperature.
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The performance of Mercury Cadmium Tellurile(MCT) infrared detecter is not only determined by electrical prameters of material, but also by the surface state of sensitive element. This paper shows, that by coating the surface of 8-12u MCT detector with an antireflecting dielectric material, reflection on the surface of sensitive element is decreased and quantum efficiency is increased therefore detectivity and responsivity are increased, usually by 15-30%.
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Many theoretical and experimental stuidies have been reported (1,2) on the metal-insulator-metal (MIM) point contact diode as a device to measure infrared optical frequencies. Electron tunnelling is the most widely accepted explanation for the extremely broadband response of MIM diodes. However, there is evidence for at least one more phenomenon, slower and possibly of thermal origin, occurring in the diode (3); this effect could be responsible of a masking effect particularly important near visible frequencies (2), where the absorption of the metals becomes greater, and tentatively contributes tc opposite polarity video detection at visible wavelengths (4). Purpose of the present work was to perform a systematic investigation on a W-Ni MIM point contact diode at different IR and FIR wavelengths. Results will be discussed which yield the determination of a cutoff for the slow mechanism and clearly demonstrate the suggested thermal origin of the effect.
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The results of scaling studies for the next generation of linear electron-positron colliders have demonstrated a need for high pulse power, high efficiency, high gain microwave (8-30 GHz) amplifiers.1 As part of our investigation into the suitability of gyrotron amplifiers for this application, we are constructing an X-band gyroklystron which is predicted to achieve a peak power of 30-50 MW2. A schematic of the major subsystems of the initial two-cavity gyroklystron is shown in Fig. 1. The modulator supplies a 500 kV, 200 A, 1.5 its pulse with an intermediate voltage to a double-anode Magnetron Injection Gun (MIG). The MIG generates a rotating beam which passes through the circuit after being adiabatically compressed. The beam's phase-space distribution is modulated by a microwave signal which is injected into the first cavity. Energy is extracted axially through a coupling aperture in the second cavity and travels through a nonlinear waveguide to a half-wavelength output window. The beam expands in the decreasing magnetic field and impinges on a 35 cm section of the output waveguide. A directional coupler and water calorimeter (not shown) measure the peak and average microwave power. The nominal parameters of this configuration are listed in Table I and details of these subsystems are discussed below.
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Multi-mode operation in an overmoded gyrotron experiment is compared with the predictions of a quasi-linear theory. The different regimes of strong and weak coupling of the TE111 mode to other modes are determined. The effects of transit time broadening and beam perpendicular energy change on mode competition is investigated. The start-up of oscillation is studied in both primed and unprimed conditions. Finally the theory is used to predict the degree of mode control obtained by a driving signal of given amplitude.
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We are studying the phase-locking of highly over-moded gyrotrons using a moderate power (~50 kW) 85 GHz two cavity TE1,3 gyroklystron oscillator. The latest experimental and theoretical results will be presented.
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Operation of linear supercolliders at a frequency above the 10-17 GHz range which is usually considered would have a number of important advantages including reduced accelerator average power consumption (~w-1), and more compact microwave pulse compression circuits. Frequency scaling of gyroklystrons is especially advantageous since peak power rating of these tubes scales as w-1, while peak power per feed required by the accelerator scales as w-2. Gyroklystron amplifiers which would be suitable for driving linear supercolliders at 30 GHz are being designed.
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The effects of AC space charge fields are included in the analysis of moderately relativistic gyrotrons. We adopt the slow time scale formalism developed by Antonsen, Manheimer and Levush [1] to describe the transverse self-fields while the electromagnetic fields are given by the cold cavity modes. Using a partially self consistent numerical code [2], simulations of multi-cavity gyroklystron amplifiers were performed. Preliminary studies indicate that there is an increase in both gain and efficiency. We believe that this increase in efficiency can be attributed to the relative weakness of the AC space charge field compared to the electromagnetic field: in high voltage, high current devices the interaction length is short so that the cavities do not self-oscillate. Because of the short interaction length the electromagnetic field must be large, making the AC space charge field small in comparison.
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The space charge limiting current in a wave cavity and in presence of electromagnetic fields is calculated in connection with application to high power gyrotrons. It is found that the ponderomotive energy alters radically the build up of beam electrostatic energy. As a consequence, the limiting current can be greatly decreased or enhanced depending on whether the ponderomotive energy is positive or negative, respecttvely. This effect can be observed experimentally and it has important practical consequences for present high-current particle beam experiments.
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In this paper a nonradiative symmetrical dielectric grating waveguide and its application to MMW DBR Gunn oscillator is presented. The width of symmetrical dielectric strips is selected carefully in order to avoid the leakage and resonance effect. A DBR oscillator has been designed and tested, Its power output is 70-100mW, and frenuency stability is better than 10-6 at 40 GHz which is 10 times better than that of MMW DBR oscillator using the inverted strip dielectric waveguide(1).
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A mode matching method for the analysis of a cylindrical dielectric resonator with arbitrarily shaped cross-section inside a waveguide is presented which allows series expansions of the fields in the region of the dielectric insert and of the waveguide with different numbers of eigenmodes. Furthermore complex modes can simply be taken into account. Resonant frequencies above the cut-off frequency of the dominant mode of the waveguide are complex due to energy radiation. The method is verified for some special cases.
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A numerical modelling procedure in the time-domain of microstrip circuits containing non-linear devices such as varactor multipliers and halversTM is described. The two-dimensional Transmission Line Matrix (TLM) method has been extended to model elements with voltage-dependent capacitance (varactors). Waveforms and spectra computed with the TLM model compare well with measured results.
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In this paper, a general finite element method as well as a graded-mesh TLM procedure for determining the dispersion characteristics, field distribution, pseudo-impedance and losses of generalized millimeter-wave transmission media are described. These methods cover arbitrary cross-sections and account for realistic features (finite metallization thickness, substrate mounting grooves etc.) that are often neglected in theoretical analysis. Dispersion characteristics and characteristic impedances obtained for dielectrically loaded ridged waveguides compare well with the available data. Conductor and dielectric losses are also computed for these structures. A modified finline structure called " ridged fin-line" is also analysed. The main advantages of this structure are its large monomode bandwidth and reduced dispersion. The cutoff frequencies of bilateral finlines in circular waveguides are also computed.
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A new phenomenon of coflow coupling between guided waves of opposite polarizations has been discovered. Numerical results are given to illustrate the effect of polarization conversions on guiding characteristics of dielectric strip waveguides.
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An open cavity model is developed to analyse end effects of slot line. Both the reactance and radiation effects are taken into account. The numerical results are compared with the published data.
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Spectral domain analyses of microstrip transmission lines on anisotropic layers are presented. Dielectric and magnetic anisotropies are considered. The dyadic Green's function in a matrix form, in combination with Galerkin's method, are used to obtain the propagation characteristics of the microstrip on ferrite and on anisotropic dielectric substrates. Curves of effective permittivities as functions of frequency are shown for microstrip lines on anisotropic dielectric substrates.
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An analysis of finlines on layered biaxial aniso-tropic dielectric substrate using the finite element method is developed. The spurious modes are eliminated by imposing the restriction ∫Ω∇.Η2dΩ = 0 to the used functional with a consequent reduction of matrix size of the resultant eigenvalue problem. The basic formulation is presented and the eigenvalue equation for the calculation of the effective dielectric constant is given.
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It is well known that single-mode behaviour of plane optical waveguides made of magnetooptical materials is of great importance in the implementation of an isolator. In this work we are going to analyze the propagation in a single mode magnetooptical waveguide by means of the "Transfer Matrix" method, which can be di-rectly applied to any multi-layer structure.
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Superconducting films have been shown to be very sensitive, broadband, low noise infrared sensors. Granular, low dimensional superconducting films of Nb, NbN, Nbn/BN as well as the high transition temperature cuprates have been studied over the last decade and shown to have unusual physical properties that make them especially suitable for use as mm-wave and infrared detectors. In this paper, this work will be reviewed with an eye toward projecting the ultimate utility of superconducting sensors
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Far-Infrared reflectivity technique over the wavenumber region 10 - 800 per centimeter was utilized to observe the surface reflection of a Y-Ba-Cu-O high temperature superconductor specimen. The specimen was introduced inside a liquid helium dewar, the tail of which passes through a two inch bore Bitter solenoid high intensity d.c. magnet.
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A far infrared study for ceramic high-Tc superconductors, T12Ba2CaCu208 and YBa2Cu307, and for an oriented YBa2Cu307 thin film is reported. We present for the ceramics, that consist of strongly anisotropic crystallites, a new method of analysis that allows to extract properties of phonons and of charge carriers. We find that the dynamical conductivity of both the ceramics and the film in the normal state can be described by Drude's theory. The reflectivity of the film in the superconducting state corresponds to a Mattis-Bardeen like behavior with an energy gap 2Δ(0)/kTc = 4.2.
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Systematic measurements of the far infrared reflection spectra of high Tc superconductors LnBa2Cu30x for various Ln as shown in the title were performed. Infrared reflection spectra of tetragonal LnBa2Cu10, exhibit Reststrahlen vibration at 640, 590, 530, 355 and 250 cm-1, common to these materials, and the spectra of the orthorhombic LnBa2Cu30x exhibit the characteristics of free carriers except PrBa2Cupx with weak phonon structures at 617, 570, 317 and 285 cm-1. PrBa2Cu3Ox is not a superconductor, and it has no characteristic broad band due to free carriers for all x in the range of 6 to 7.
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A versatile microwave/millimeter-wave characterization technique using cylindrical resonance cavities has been implemented which allows measurement of the absorption and sheet resistivity of high-temperature superconductor (HTS) powders, films, and bulk samples. Copper and YBa2Cu307_x (1-2-3) powders were compared with bulk samples to provide input for a simple model of microwave conductivity in bulk HTS materials. While the conductivity of copper metal is more than twice that of bulk YBa2Cu307_x at 77 K, the conductivity of copper powder at this temperature is less than that of the HTS powder.
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A simple RF measurement method using a resonant strip in a waveguide has been developed. The method has been used to measure the RF properties of different superconducting materials. The results of Q and loss measurements will be presented.
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The National Synchrotron Light Source (NSLS) is a very bright, pulsed, broadband IR source. Continuously covering the spectral range from the visible to the mm wave region, it has been calculated&apos 1,2 to be one to three orders of magnitude brighter than a black-body source. At wavelengths longer than 100p, (100 cm 1) the NSLS provides more flux than a standard glbbar source, due to the different power laws governing black-body radiation and synchrotron radiation emission.
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A beat-note stability of 500 Hz over 1 second has been observed between two free-running optically pumped NH3 lasers. The 12 μm laser frequency is strongly isolated from cavity-mirror motion, and is relatively insensitive to perturbations in the pump lasers. The NH3 lasers have been used to observe Lamb-dips in external NH3 cells.
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