The eXTP (enhanced X-Ray Timing and Polarimetry) mission is a Chinese science space mission developed in collaboration with many international countries. Devoted to observations in the X-ray band, with imaging, spectroscopic, timing and polarimetry capabilities, is now entering phase B. The payload includes 9 Spectroscopic Focusing Array (SFA) and 4 Polarimetry Focusing Array (PFA) telescopes. The SFA telescopes, equipped with SDDs, have a spatial resolution of 1 arcmin, while the PFA telescopes, equipped with imaging gas pixel photoelectric polarimeters, have a spatial resolution of 30 arcsec. Both optics work in the 0.5-10 keV range with a focal length of 5.25 m and a field of view of 12 arcmin. The technology used for the optics production is Nickel electroforming from super-polished mandrels, like many previous successful X-ray missions. The reflecting coating is a double layer Au+C, which ensures optimal response at high and low energies. The PFA and SFA have the same optical design, in order to minimize the number of mandrels to be produced. In this paper, we present the optical design of these telescopes assisted with raytracing and a preliminary concept for the mechanical design supported by FEM simulation.
Micro-channel Plates(MCPs) are an important part of ultraviolet photon counting imaging detectors. They can intensify single particles or photons by the multiplication of electrons via secondary emission.Thus, the MCP gain has an very important influence on the performance of ultraviolet photon counting imaging detectors. In this article, influence of MCP gain on decoding accuracy is studied by using Monte Carlo method. Simulation results show that decoding error is large when MCP gain is low,and MCPs shoud have at least 106 gain to ensure accurate decoding. At the same time, influence of MCP gain on decoding error was tested by using ultraviolet photon counting imaging system based on TWA(Tetra Wedge Anode,TWA). Experimental results are consistent with the theoretical analysis and simulation.
Cesium iodide (CsI) photocathode is widely used in various UV (ultraviolet) detecting devices because of its high quantum efficiency (QE) and good stability under short exposure to humid air. In this paper, the performance of the opaque CsI photocathode is studied, including imaging performance, influence of humidity on the quantum efficiency and the stability of the CsI photocathode under FUV irradiation. In the experiment, the input surface of the MCP was evenly divided into four parts. Different thicknesses of the CsI photocathode were deposited directly on the front surface of micro-channel plates (opaque photocathode). The response of different thicknesses and the stability of UV quantum efficiency of CsI photocathode under FUV illumination were studied by using UV monochromator. At the same time, the influence of humid air exposure on the quantum efficiency of CsI photocathode was tested. According to the experimental results, a FUV detector (vacuum tube) based on opaque CsI photocathode was fabricated and the quantum efficiency of the detector was tested. Absolute quantum efficiency of the FUV detector is over 15.5% at 121nm.
X-ray grazing incidence optics are widely used in X-ray astronomy, especially for imaging payloads Wolter optics are the most workhorse. However, as there are two cascaded mirrors in Wolter type, the efficiency is quite low after two reflections. In this paper a kind of nested conical concentrator is developed with only one reflection to concentrate the X-ray photons and obtain the timing information. The mirror length is 200mm, the mirror foils cover from 38.8 to 100mm in diameter. D263T glass of 0.3mm thickness is used as mirror substrate with Iridium film deposited in order to improve the X-ray reflection. The D263T glass is slumped at 580°C with precisely machined and polished mold. 3D printed resin serves as upper mold for glass cutting. The quality of mirror substrate is mainly determined by the surface of forming mandrel. As the surface roughness is quite important for X-ray reflection, after deposition it is tested with interferometer and AFM, and the roughness is 0.6nm. Mirror integration based on visible light is built, and the conical mirrors are assembled and adjusted by real time monitoring for the focal point of visible light. With the monochromic X-ray source, the concentrator efficiency is tested as email@example.comV, firstname.lastname@example.orgV. The focal point is Φ8.2mm in Xray, with 80% of its energy encircled in a 4mm width. This kind of X-ray concentrator could be used in X-ray navigation, X-ray communication and other X-ray timing astronomy.
A novel space communication method is presented in this paper based on X-ray photons. As a result of its short
wavelength and great penetrability, X-ray has no attenuation for transmission in space when its photon energy is
more than 10keV (λ<0.1nm). Thus a communication technology of long distance signal transmission in space can
be achieved with smaller volume, lower weight and lower power. Therefore, X-ray communication (XCOM) is
especially valuable to the deep space missions, which will be able to realize higher data rates, smaller SWAP than
with RF and laser communications. Using X-ray photons as information carrier will not only be a good complement
to laser and RF communications, but will also have unique applications when RF and laser signals are not available
like the spacecraft’s re-entering to the earth. High-speed modulation and high-sensitivity detection of X-rays are
two major technical issues which should be addressed in order for the X-ray communication to take place. A
Grid-controlled Modulated X-ray tube (GMXT) is proposed and developed as X-ray transmitter. One or more
specially designed grid electrodes are added to the traditional X-ray tube to modulate the electrons. The
communication signal is coded and applied to the modulated grid electrode, and then the corresponding X-ray
signals are generated and sent out. X-ray detector based on micro-channel plate(MCP) is used as communication
receiver because of its high temporal resolution. An audio communication experiment system based on XCOM is
setup in laboratory including the X-ray transmitter and the receiver. X-ray communication is successfully
demonstrated and the communication speed reaches 64 kilobits per second in a vacuum tube of 6 meters long. As a
new concept of space communication, X-ray communication will have more important scientific significance and
application prospects when technologies for X-ray modulation and detection are further developed.
This paper describes the preliminary design and performances of a new developed photon counting imaging detector for
Chinese ChangE-2 EUV explorer mission. The detector consists of microchannel plate (MCP) stacks and wedge and
strip anode and corresponding data read out electronics. The experimental results shows that the new developed detector
has a spatial resolution of about 75μm, image distortions are small and dark noise count rate less than 0.4 counts cm-2s-1.
The pulse height distribution vs MCP operating voltages and the flat field performances are also discussed.
The femtosecond electron diffraction (FED) is a unique method for the study of the changes of complex molecular
structures, and has been specifically applied in the investigations of transient-optics, opto-physics, crystallography,
and other fields. The FED system designed by the present group, consists of a 35nm Ag photocathode evaporated on
an ultraviolet glass, an anode with a 0.1mm aperture, two pairs of deflection plate for the deflection of electron beams
in X and Y directions, and the Y deflection plate can be used as a scanning plate while measuring the pulse width of
electron beams, the double MCPs detector for the enhancing and detecting of electron image. The magnetic lens was
used for the focusing of the electron beams, and the focal length is 125mm. The distance between the object(the
photocathode) and the image(the sample) is 503mm, and the size of electron beams is smaller than 17microns after
focusing, the convergence angle is of -0.075~0.075°, and the temporal resolution is better than 350fs.