Tom Archuleta

Gated x-ray detector for the National Ignition Facility

Two new gated x-ray imaging cameras have recently been designed, constructed, and delivered to the National Ignition Facility in Livermore, CA. These gated x-Ray detectors are each designed to fit within an aluminum airbox with a large capacity cooling plane and are fitted with an array of environmental housekeeping sensors. These instruments are significantly different from earlier generations of gated x-ray images due, in part, to an innovative impedance matching scheme, advanced phosphor screens, pulsed phosphor circuits, precision assembly fixturing, unique system monitoring, and complete remote computer control. Preliminary characterization has shown repeatable uniformity between imaging strips, improved spatial resolution, and no detectable impedance reflections.

TRIDENT high-energy-density facility experimental capabilities and diagnostics

The newly upgraded TRIDENT high-energy-density (HED) facility provides high-energy short-pulse laser-matter interactions with powers in excess of 200 TW and energies greater than 120 J. In addition, TRIDENT retains two long-pulse (nanoseconds to microseconds) beams that are available for simultaneous use in either the same experiment or a separate one. The facilitys flexibility is enhanced by the presence of two separate target chambers with a third undergoing commissioning. This capability allows the experimental configuration to be optimized by choosing the chamber with the most advantageous geometry and features. The TRIDENT facility also provides a wide range of standard instruments including optical, x-ray, and particle diagnostics. In addition, one chamber has a 10 in. manipulator allowing OMEGA and National Ignition Facility (NIF) diagnostics to be prototyped and calibrated.

A high-resolution x-ray microscope for laser-driven planar-foil experiments

A soft x-ray microscope (E≲3 keV) with high spatial resolution (∼3 μm) has been characterized at the University of Rochester’s Laboratory for Laser Energetics and used for initial experiments on the Omega laser system [Boehly et al., Opt. Commun. 133, 495 (1997)] to study the hydrodynamic stability of directly driven planar foils. The microscope, which is an optimized Kirkpatrick–Baez-type design, is used to obtain four x-ray radiographs of laser-driven foils. Time-resolved images are obtained with either custom-built framing cameras (time resolution ∼80 ps) or by using short-pulse backlighter beams (Δt≲200 ps). In the former case, a spatial resolution of ∼7 μm was obtained (limited by the framing camera), while in the latter case a resolution of ∼3 μm was obtained. This paper details the testing, calibration, and initial use of this microscope in the laboratory and on Omega.

The large format x-ray imager

We introduce a new Large Format X-ray Imaging Camera (LFC) for the Los Alamos National Laboratory (LANL) Inertial Confinement Fusion/Radiation Physics (ICF/RP) program. This instrument is intended as a prototype for use at the National Ignition Facility (NIF), but is capable of operating at LANL’s Trident and the University of Rochester’s OMEGA laser systems. The LFC is based upon similar x-ray camera architecture and is currently in the final design stages. It is constructed around a mosaic of 3 large (35×105 mm2) microchannel plate (MCP) detectors, primarily to give a larger field of view, but also for greater temporal coverage and higher magnification while maintaining spatial resolution. The camera is designed to have 30 data channels, six 13-mm-wide microstrips, continuous temporal coverage of 4.2 ns, adjustable electrical gate width, and variable gain on each microstrip and magnifications up to 20×. In the process of designing the LFC we scrutinized every element of the gated x-ray imaging process a...

Multipurpose 10 in. manipulator-based optical telescope for Omega and the Trident laser facilities

We have recently designed and are building a telescope which acts as an imaging light collector relaying the image to an optical table for experiment dependent analysis and recording. The expected primary use of this instrument is a streaked optical pyrometer for witness plate measurements of the hohlraum drive temperature. The telescope is based on the University of Rochester’s 10 in. manipulator (TIM) which allows compatibility between Omega, Trident, and the NIF lasers. The optics capture a f/7 cone of light, have a field of view of 6 mm, have a spatial resolution of 5–7 μm per line pair at the object plane, and are optimized for operation at 280 nm. The image is at a magnification of 11.7×, which is convenient for many experiments, but can be changed using additional optics that reside outside the TIM.

DUAL MICROCHANNEL PLATE MODULE FOR A GATED MONOCHROMATIC X-RAY IMAGER

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 four channel Kirkpatrick–Baez microscope and diffraction crystals and is located at the 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=40, MCPs have a 10.2 mm wide, 8 ohm stripline constructed of 500 nm copper overcoated 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.

A large-format gated x-ray framing camera

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.

Quantitative x-ray imager (abstract)

We report on development of a quantitative x-ray imager (QXI) for the national Inertial Confinement Fusion Program. Included in this development is a study of photocathode response as a function of photon energy, 2–17.5 keV, which is related to diagnostic development on the National Ignition Facility (NIF). The QXI is defined as being a quantative imager due to the repeated characterization. This instrument is systematically checked out, electronically as well as its photocathode x-ray response, both on a direct current and pulsed x-ray sources, before and after its use on a shot campaign. The QXI is a gated x-ray imager1 used for a variety of experiments conducted in the Inertial Confinement Fusion and Radiation Physics Program. The camera was assembled in Los Alamos and has been under development since 1997 and has now become the workhorse framing camera by the program. The electronics were built by Grant Applied Physics of San Fransisco, CA.2 The QXI has been used at the LANL Trident, LLNL Nova, and Un...

Calibration of gated MCP responses in the x-ray region: spatial gain variation

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.

Optimization of gated x-ray intensifier screens

Gated x-ray intensifiers are primary imaging diagnostics in high energy density physics and inertial confinement fusion experiments. We describe recent work in optimization of the phosphor screens used in these intensifiers. One avenue for improvement in resolution, contrast, and brightness is improved phosphor screens. Efforts have been directed at improving luminosity, resolution, and contrast with an aluminized thin (<0.7μg∕cm2) phosphor layer, a higher transmission indium tin oxide (ITO) electrode, and higher density screens. Thinner phosphors, coupled with thinner aluminum overcoats (<500A), should give equivalent or higher luminosities than traditional thick (<0.7μg∕cm2) settled coatings in the electron energy range between 3 and 5kV, typical microchannel plate to screen accelerating voltages for this class of instrument. Higher resolution is achieved by coupling increased extraction voltage (ph∕e-) with less interparticle photon diffusion and increased photon capture (aluminum overcoat). The contri...