V. Fatherley, L. Goodwin, D. Schmidt, S. Batha, N. Cordes, V. Geppert-Kleinrath, H. Jorgenson, J. Martinez, T. Murphy, J. Oertel, M. Springstead, C. Wilde, P. Volegov
The LANL neutron imaging and fabrication teams completed the fabrication and inspection of the neutron imaging aperture for the National Ignition Facility (NIF) prior to first use in December 2018. The 16 layer aperture contains an array of 87 openings, manufactured by scribing 100 profiles along 20-cm lengths of thin gold foils. The openings consist of 15 penumbral and 72 triangular apertures. The 16 layers are then assembled into a single 15-mm x 16.6-mm x 200- mm component. Images produced from the array of apertures must be deconvolved in order to remove distortions caused by the extended length of the aperture. In order to deconvolve the image, the as-built aperture profile must first be characterized by measuring the scribed apertures at multiple places along their length. Equipment used for inspections included a white-light interferometer, a confocal laser scanner, and an optical coordinate measuring machine. Both sides of each layer were individually inspected, using complementary and overlapping capabilities in order to overcome the aspect ratio and feature size challenges. The result was a three dimensional, as-built model with the interior layer inspection detail overlaid to create a complete as-built model of the aperture array. This paper provides an overview of the purpose of the aperture array and a detailed discussion of the aperture inspection strategies, technology processes and challenges.
Neutron imagers based on thick apertures have become important diagnostics for the shape and size of the burning and cold fuel regions of inertial confinement fusion sources for high-energy density physics. Over time, the designs of these apertures have changed to meet the requirements of newer sources and taken advantage of improvements in manufacturing and alignment technology. In this paper, we discuss the evolution of thick apertures for neutron imaging at laser-driven ICF facilities. We describe the parameters that define the apertures and the apertures that have been fabricated and fielded. We also discuss the lessons learned with each iteration. We also discuss the impact that added features such as collinear or near-collinear γ-ray and x-ray imaging systems have had on the designs of the aperture arrays.
Frank Lopez, Hans Herrmann, Ramon Leeper, Steve Batha, John Oertel, Jeffrey Griego, Brian Steinfeld, Paul Polk, Lynne Goodwin, Valerie Fatherley, Thomas Archuleta, Robert Aragonez, Benjamin Pederson, John Celeste, Robin Hibbard, Arthur Carpenter, Jose Hernandez, Jorge Carrera, Hesham Khater, Eric Downing, Nicholas St. Hilaire, Shiva Sitaraman
Fielding the LANL third-generation Gas Cherenkov Detector (GCD-3) at the National Ignition Facility (NIF) revealed an
array of complex engineering challenges. Fielding the GCD-3 Detector in a 3.9 meter re-entrant Well on the NIF Target
Chamber required the development of a specialized detector deployment system named the WellDIM3.9m Diagnostic
Manipulator (WellDIM). The most stringent design requirement entailed a no-load/no-contact condition with the Well, which
dictated that all seismic loads be transferred to the Target Chamber port flange. The WellDIM transports the GCD-3 into the
Well at a distance of 3.9m from Target Chamber Center. The GCD-3 Detector, outfitted with additional shielding to mitigate
higher NIF backgrounds, will serve as a prototype for the future, heavily shielded “Super-GCD”.
V. Fatherley, S. Batha, C. Danly, L. Goodwin, H. Herrmann, H. Jorgenson, J. Martinez, F. Merrill, J. Oertel, D. Schmidt, P. Volegov, C. Wilde, D. Fittinghoff, M. Ayers, D. Barker, G. Grim, R. Hibbard, N. Shingleton, M. Vitalich
A new neutron imager, known as Neutron Imaging System North Pole, has been fielded to image the neutrons produced in the burn region of imploding fusion capsules at the National Ignition Facility. The resolution and alignment requirements and parameters that drive the design of this system are similar to the pre-existing equatorial system, there are significant changes. This work describes the parameters and limitations driving the design of this system, discusses the metrology and alignment, and shows some data from the instrument.
A new neutron imager, known as Neutron Imaging System North Pole, will use an array of thick apertures to image the
neutrons produced in the burn region of imploding fusion capsules at the National Ignition Facility. While the resolution
requirements and parameters that drive the design of this array are similar to traditional x-ray pinhole arrays, neutrons
require thick apertures with narrow fields of view, and a precisely designed array of apertures is critical to allow
alignment and capture the required images with 10-μm resolution. This work describes the mechanical parameters and
limitations driving the design of the aperture array, in addition metrology and alignment requirements are discussed.
We will describe the installation and wavelength calibration of a multiple monochromatic imager [MMI]1 to be used on mix experiments at National Ignition Facility [NIF]2. The imager works between 8 and 13 keV, has a spatial resolution of 16 micrometers and generates many images each with an energy bandwidth of ~80 eV. The images are recorded either on image plates or on gated x-ray detectors. We will describe: how we aligned the instrument on the bench using visible light, how we checked the alignment and determined the energy range using a k-alpha x-ray source, and how we installed and aligned the instrument to the NIF target chamber.
G. Grim, G. Morgan, R. Aragonez, T. Archuleta, D. Bower, C. Danly, O. Drury, J. Dzenitis, V. Fatherley, B. Felker, D. Fittinghoff, N. Guler, F. Merrill, J. Oertel, C. Wilde, M. Wilke
One of the scientific goals of the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory, Livermore CA, is to obtain thermonuclear ignition by compressing 2.2 mm diameter capsules filed with deuterium and tritium to densities approaching 1000 g/cm3 and temperatures in excess of 4 keV. Thefusion reaction d + t → n + a results in a 14.03 MeV neutron providing a source of diagnostic particles to characterize the implosion. The spectrum of neutrons emanating from the assembly may be used to infer the fusion yield, plasma ion temperature, and fuel areal density, all key diagnostic quantities of implosion quality. The neutron time-of-flight (nToF) system co-located along the Neutron Imaging System line-of-site, (NIToF), is a set of 4 scintillation detectors located approximately 27.3 m from the implosion source. Neutron spectral information is inferred using arrival time at the detector. The NIToF system is described below, including the hardware elements, calibration data, analysis methods, and an example of its basic performance characteristics.
David Clark, Robert Aragonez, Thomas Archuleta, Valerie Fatherley, Albert Hsu, Justin Jorgenson, Danielle Mares, John Oertel, Kevin Oades, Paul Kemshall, Philip Thomas, Trevor Young, Neal Pederson
Gated X-Ray Detectors (GXD) are considered the work-horse target diagnostic of the laser based inertial confinement fusion (ICF) program. Recently, Los Alamos National Laboratory (LANL) has constructed three new GXDs for the Orion laser facility at the Atomic Weapons Establishment (AWE) in the United Kingdom. What sets these three new instruments apart from what has previously been constructed for the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) is: improvements in detector head microwave transmission lines, solid state embedded hard drive and updated control software, and lighter air box design and other incremental mechanical improvements. In this paper we will present the latest GXD design enhancements and sample calibration data taken on the Trident laser facility at Los Alamos National Laboratory using the newly constructed instruments.
The National Ignition Facility will begin testing DT fuel capsules yielding greater than 1013 neutrons during 2010.
Neutron imaging is an important diagnostic for understanding capsule behavior. Neutrons are imaged at a scintillator
after passing through a pinhole. The pixelated, 160-mm square scintillator is made up of 1/4 mm diameter rods 50 mm
long. Shielding and distance (28 m) are used to preserve the recording diagnostic hardware. Neutron imaging is light
starved. We designed a large nine-element collecting lens to relay as much scintillator light as reasonable onto a 75 mm
gated microchannel plate (MCP) intensifier. The image from the intensifier's phosphor passes through a fiber taper onto
a CCD camera for digital storage. Alignment of the pinhole and tilting of the scintillator is performed before the relay
lens and MCP can be aligned. Careful tilting of the scintillator is done so that each neutron only passes through one rod
(no crosstalk allowed). The 3.2 ns decay time scintillator emits light in the deep blue, requiring special glass materials.
The glass within the lens housing weighs 26 lbs, with the largest element being 7.7 inches in diameter. The distance
between the scintillator and the MCP is only 27 inches. The scintillator emits light with 0.56 NA and the lens collects
light at 0.15 NA. Thus, the MCP collects only 7% of the available light. Baffling the stray light is a major concern in the
design of the optics. Glass cost considerations, tolerancing, and alignment of this lens system will be discussed.
The gain spectrum in a gated multichannel intensifier output depends on the gain and spatial averaging. The spectrum
affects the minimum signal that can be detected as well as the signal to noise in the detected images. We will present
data on the gain-spectrum for the GXD detector, a gated x-ray detector to be used at the National Ignition Facility. The
data was recorded on a cooled CCD detector, with an x-ray gating time of approximately 75 ps, selected from a range of
0.2 and 1 ns electrical pulse width determined by pulse forming modules were also used. The detector was characterized
at the TRIDENT laser facility, using a 2.4 ns long x-ray at 4.75 keV. The x-rays were generated by the interaction of the
focused Trident laser beam with a Titanium target.
G. Grim, R. Day, D. Clark, V. Fatherley, F. Garcia, S. Jaramillo, A. Montoya, G. Morgan, J. Oertel, T. Ortiz, J. Payton, P. Pazuchanics, D. Schmidt, A. Valdez, C. Wilde, M. Wilke
Neutron imaging of Inertial Confinement Fusion (ICF) targets provides a powerful tool for understanding the
implosion conditions of deuterium and tritium filled targets at Mega-Joule/Tera-Watt scale laser facilities. The
primary purpose of imaging ICF targets at that National Ignition Facility (NIF), sited at Lawrence Livermore
National Laboratory, Livermore, California, is to determine the asymmetry of the fuel in an imploded ICF
target. The image data are then combined with other nuclear information to gain insight into the laser and
radiation conditions used to drive the target. This information is requisite to understanding the physics of
Inertial Confinement Fusion targets and provides a failure mode diagnostic used to optimize the conditions
of experiments aimed at obtaining ignition. We present an overview of neutron aperture imaging including a
discussion of image formation and reconstruction, requirements for the future (NIF) neutron imaging systems,
a description of current imaging system capabilities, and ongoing work to affect imaging systems capable of meeting future system requirements.
We will discuss our attempts to measure of the absolute gain and its variation across the face of fast gated multichannel
plate [MCP] detectors for 4.75 keV x-rays. We found that some of the gated strips had variations in the gain along and
perpendicular to the direction of travel, and significant variation along the time axis that requires these calibrations to
obtain the correct time history of gated events. We will also present some of the results on the linearity of such gain
with input x-ray signal amplitude.
We describe a gated microchannel plate (MCP) based Quantitative X-ray Imager (QXI) developed by Los Alamos National Laboratory (LANL) and measure some of its performance characteristics. Such imagers use propagating electrical pulses along microstrips on the MCP to quickly gate on and off portions of the strip and hence provide fast framing capability (typically 100 ps frames with up to 1 ns time coverage). Three issues have been quantitatively studied using the QXI and another similar but older LANL gated x-ray framing camera, the GXI-T: QXI pulse shapes generated by its pulse-forming modules: GXI-T optical pulse widths as a function of incident UV energy on the microchannel plate: and the modulation transfer function (MTF) of the QXI intensifier.
The design, construction and implementation of a large format gated x-ray camera (LFC) for the LANL inertial confinement fusion/ radiation physics program is described. The active area of the detector is 105 mm x 105 mm using three 35 mm x 105 mm microchannel plates (MCP), that are proximity focused to a monolithic P-43 phosphor screen. Gating of the six independent, 13 mm, tall electrical microstriplines, deposited on the MCP, is accomplished by six individually biased and delayed high-voltage electrical pulses. The electrical gating pulse is continuously adjustable from 200 ps to 1300 ps, yielding optical shutters of 80 ps to 1000 ps. All electrical functions are computer controlled and monitored. Images are created on the striplines by conventional x-ray pinhole image techniques and recorded by film or a 4096 x 4096 CCD camera that is fiberoptically coupled to the back of the phosphor screen. Construction is complete and the instrument is now operated on a routine basis at local and remote laser facilities. Detailed characterization of the camera is in progress.
Development and testing of a dual microchannel plate (MCP) module to be used in the national Inertial Confinement Fusion (ICF) program has recently been completed. The MCP module is a key component of a new monochromatic x-ray imaging diagnostic which is designed around a 4 channel Kirkpatrick-Baez microscope and diffraction crystals and is located at University of Rochester's Omega laser system. The MCP module has two separate MCP regions with centers spaced 53 mm apart. Each region contains a 25 mm MCP proximity focused to a P-11 phosphor coated fiberoptic faceplate. The two L/D equals 40, MCPs have a 10.2 mm wide, 8 ohm stripline constructed of 500 nm copper over-coated with 100 nm gold. A 4 kV, 150 ps electrical pulse provides an optical gatewidth of 80 ps and spatial resolution has been measured at 20 lp/mm.
We have recently developed a gated monochromatic x-ray imaging diagnostic for the national Inertial-Confinement Fusion program. This new imaging system will be one of the primary diagnostics to be utilized on University of Rochester's Omega laser fusion facility. The new diagnostic is based upon a Kirkpatrick-Baez microscope dispersed by diffraction crystals, as first described by Marshall and Su. The dispersed images are gated by four individual proximity focused microchannel plates and recorded on film. Spectral coverage is tunable up to 8 keV, spectral resolution has been measured at 20 eV, temporal resolution is 80 ps, and spatial resolution is better than 10 micrometers .
We have implemented two different types of 40 ps framing camera configurations on the Nova laser system. We will describe the configurations of both systems as well as discuss the advantages of each.
The pulsed characteristics of gated, microstrip configuration microchannel-plate (MCP) detectors used in x-ray framing cameras deployed on laser plasma experiments worldwide are examined in greater detail. The detectors are calibrated using short (20 ps) and long (500 ps) pulse x-ray irradiation and 3 - 60 ps, deep UV (202 and 213 nm), spatially-smoothed laser irradiation. Two-dimensional unsaturated gain profiles show < 5% long-range transverse variations but up to 3 dB/cm drop in gain parallel to the pulse propagation direction. Up to 50% gain enhancements due to voltage reflection from the bends of a meander stripline geometry and from the ends of conventional straight striplines are also observed. Reproducible gate profiles are obtained with either picosecond x-ray or UV bursts and FWHM extracted with 3 picosecond accuracy. A novel single-shot method for measuring local gate propagation speeds using a tilted MCP is also demonstrated.
High-speed, high x-ray energy imaging of implosions is a key diagnostic technique in the glass laser implosion program in the USA. With the correct x-ray energy, time-gated images can measure the symmetry and mix of the imploding shell into the stagnated fuel if the spatial resolution of 10 or 5 micrometers matched by a temporal resolution of 100 or 50 psec. Several 100 psec microchannelplate (MCP) x-ray pin hole cameras have bee installed and run on large laser systems with improving reliability. To increase the sensitivity of the imaging system, a ring aperture microscope has been coupled to a gated MCP detector allowing imaging at up to 8 keV.
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