Development of backlighting sources for a Compton radiography diagnostic of inertial confinement fusion targets (invited)

Abstract

We present scaled demonstrations of backlighter sources, emitting bremsstrahlung x rays with photon energies above 75 keV, that we will use to record x-ray Compton radiographic snapshots of cold dense DT fuel in inertial confinement fusion implosions at the National Ignition Facility (NIF). In experiments performed at the Titan laser facility at Lawrence Livermore National Laboratory, we measured the source size and the bremsstrahlung spectrum as a function of laser intensity and pulse length from solid targets irradiated at 2x10(17)-5x10(18) W/cm(2) using 2-40 ps pulses. Using Au planar foils we achieved source sizes down to 5.5 microm and conversion efficiencies of about 1x10(-13) J/J into x-ray photons with energies in the 75-100 keV spectral range. We can now use these results to design NIF backlighter targets and shielding and to predict Compton radiography performance as a function of the NIF implosion yield and associated background.

Photometric study of single-shot energy-dispersive x-ray diffraction at a laser plasma facility

“…Thomson scattering experiments at laser plasma facilities have measured the inelastic portion of ( ) using narrow pulse backlighters for illumination 25,27,28,[57][58][59][60] . Above 2 keV, a broad-band thermal backlighter has approximately 100 times the photon conversion efficiency of a short-pulse Cu K  backlighter (Fig.…”

Shock-tuned cryogenic-deuterium-tritium implosion performance on Omega

“…Measuring the areal density of highly compressed cryogenic-DT fuel is a relatively new challenge for the ICF program, and there are few options available. It should be possible to generate a transmission Compton radiograph 23 Fig. 2͑b͒.…”

Simulation and analysis of time-gated monochromatic radiographs of cryogenic implosions on OMEGA

“…Radiography in its many forms has been a standard tool throughout the history of ICF [1,15]. Implosion radiography on OMEGA has progressed from room-temperature targets [20], to the first radiography of cryogenic targets [21,22], and to the first attempts at Compton radiography [23]. More recently, x-ray radiography has been used with gas-filled roomtemperature targets to measure nonspherical shell distortions of targets imploded with polar direct drive [20,24] and to measure the implosion velocity and mass ablation rate of capsules imploded on the NIF with indirect drive [25].…”

“…Following the implosion closer to the time of peak compression, compression and convergence raise the optical thickness of the shell very rapidly, requiring higher backlight energies to keep the shell's optical thickness within a measurable range of radiographic transmission, roughly midway between completely transparent and completely opaque, but the core self-emission also rises rapidly as the core compresses. In the hard-backlighter limit, where the self-emission spectrum has fallen off completely, Compton radiography may provide an alternative to soft x-ray radiography at stagnation [23].…”