I n e r t i a l confinement fusion experiments generate thermonuclear neutrons on subnanosecond time scales. To understand the burning o f DT f u e l , we have developed a 14 MeV neutron detector w i t h subnanosecond time response. bulk GaAs w i t h electron-hole recombination times o f 60 ps. by the energy deposited by the neutrons i n t e r a c t i n g i n the detector t h a t create f r e e c a r r i e r s . The f a s t electron hole recombination time o f t h i s material q u i c k l y removes these r a d i a t i o n generated c a r r i e r s from the conduction process r e s u l t i n g i n extremely f a s t response times. The measurements and calculations o f the s e n s i t i v i t y o f these detectors t o 14 MeV neutrons are i n good agreement. The detectors are made o f neutron damaged, The conductivity o f the detector i s modulated I n t r o d u c t i o n The design, construction and t e s t i n g o f subnanosecond neutron detection systems i s a formidable task, but t h i s c a p a b i l i t y i s important t o the understanding o f the physics of i n e r t i a l confinement fusion (ICF) implosion experiments which can produce subnanosecond bursts o f 14 MeV neutrons. consisting o f a high speed detector and s i n g l e shot recording system which record pulses o f neutrons w i t h less than 200 ps time resolution. The detector i s bulk GaAs t h a t has been neutron damaged t o decrease the e l e c t r o n and hole recombination times. This i s important because the speed of response i s a d i r e c t r e s u l t of the recornbination o f r a d i a t i o n induced c a r r i e r s i n the detector, 1.e.. the conductivity o f the detector i s modulated by the i n c i d e n t r a d i a t i o n . c a l c u l a t e the s e n s i t i v i t y of these detectors, one must c a l c u l a t e the power deposition by the neutrons i n the detectors and the f r a c t i o n of t h i s power t h a t i s used t o generate f r e e c a r r i e r s (free c a r r i e r generation r a t e ) . I n addition, the electron and hole recombination times and m o b i l i t i e s must be known and the detector placed i n an environment t h a t mfnimizes the gamma-ray and scattered neutron background. W e have b u i l t a system To The Desian of the Detector System The goal o f t h i s e f f o r t was t o produce a detector t h a t could measure the temporal h i s t o r y o f the thermonuclear burn i n an ICF experiment, not t o measure s i n g l e neutrons w i t h high speed. Computer simulations i n d i c a t e t h a t i d e a l implosions w i l l produce neutron pulses w i t h the FWHM i n the range o f 30 t o 200 ps. This pulse width i s a s e n s i t i v e measure o f the q u a l i t y o f an implosion. demonstrated t h a t we can bui I d sol id-state detectors w i t h FWHM o f less than 60 ps f o r electro-magnetic r a d i a t i o n . This technology has been used d i r e c t l y t o f a b r i c a t e the detector used t o measure neutrons. The detector i s 1 x 1 x 3 mm piece o f GaAs. The damaging was done t o the material...

To accurately measure pulse amplitude, shape, and relative time histories of optical signals with an optical streak camera, it 1s necessary to correct each recorded Imaqe for spatially-dependent qain nonunlformlty and geometric distortion. Gain nonunlformltles arise from sensitivity variations 1n the streak-tube photocathode, phosphor screen, fmaqe-lntenslfler tube, and 1maqe recordInq system. These nonunfformities may be severe, and have been observed to be on the order of 100* for some ILNL optical streak cameras,. Geometric distortion due to ootlcal couplings, electron-optics, and sweep nonllnearity not only affects pulse position and tlmlnq measurements, but affects Pulse amplitude and shape measurements as well. By using a l.053-um, long-pulse, hiqh-oower laser to generate * spatially and temporally uniform source as Input to the streak camera, the combined effects of flat-field response and geometric distortion can be measured under the norma? dynamic operation of cameras with S-l photocathodes. Additionally, by us-tnq the sane laser system to generate a train of short pulses that can be spatially modulated at the Input of the streak camera, we can effectively create a two-dimensional grid of equally-soaced pulses. This allows a dynamic measurement of the geometric distortion of the streak camera. We win discuss the techniques involved in performing these calibrations, will present some of the measured results for LLNL optical streak cameras, and will discuss software methods to correct for these effects.

A new streak camera readout system has been developed at Lawrence Livermore National Laboratory. Streak cameras are used on the Nova laser at Livermore to monitor laser beam performance and measure experimental phenomena during target irradiation experiments. In this new system, the streak camera's optical output image is lens coupled to a thermoelectrically cooled CCD camera where the streaked image is captured. The captured image is then digitized to 14 bits and transferred to Q -bus video image buffers via a DMA (direct memory access) transfer.The captured image can then be analyzed and manipulated while resident in the image buffers or saved on disk for future reference.Basic image analysis software has been written that include background subtraction, both horizontal and vertical lineouts with and without pixel averaging, pseudo coloring, and image histograms. This new system has improved dynamic range, spatial resolution, and lower noise than any of our previous readout systems. All major system components are available commercially providing a lower cost for multiple systems and simplifying future maintenance.

We describe recent, energetics performance results on the engineering preamplifier module (PAM) prototype located in the front end of the 1.8MJ National Ignition Facility (NIF ) laser system. Three vertically mounted subsystem located in the PAM provide laser gain as well as spatial beam shaping. The first subsystem in the PAM prototype is a diode pumped, Nd:glass, linear, TEMoo , 4.5m long regenerative amplifier cavity. With a single diode pumped head, we amplify a lnJ, mode matched, temporally shaped (= 20ns) seed pulse by a factor of approximately 10 to 20mJ. The second subsystem in the PAM is the beam shaping module, which magnifies the gaussian output beam of the regenerative amplifier to provide a 30mm X 30mm square beam that is spatially shaped in two dimensions to pre-compensate for radial gain profiles in the main amplifiers. The final subsystem in the PAM is the 4-pass amplifier which relay images the 1mJ output of the beam shaper through four gain passes in a $5cm X 48cm flashlamp pumped rod amplifier, amplifying the energy to 175. The system gain of the PAM is 10". Each PAM provides 35 of injected energy to four separate main amplifier chains which in turn delivers 1.8MJ in 192 frequency converted laser beams to the target for a broad range of laser fusion experiments.

This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may be made before publication, this preprint is made available with the un derstanding that it will not be cited or reproduced without the permission of the author.