Barry E. Schwartz

Spectrometry of charged particles from inertial-confinement-fusion plasmas

High-resolution spectrometry of charged particles from inertial-confinement-fusion (ICF) experiments has become an important method of studying plasma conditions in laser-compressed capsules. In experiments at the 60-beam OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)], utilizing capsules with D2, D3He, DT, or DTH fuel in a shell of plastic, glass, or D2 ice, we now routinely make spectral measurements of primary fusion products (p, D, T, 3He, α), secondary fusion products (p), “knock-on” particles (p, D, T) elastically scattered by primary neutrons, and ions from the shell. Use is made of several types of spectrometers that rely on detection and identification of particles with CR-39 nuclear track detectors in conjunction with magnets and/or special ranging filters. CR-39 is especially useful because of its insensitivity to electromagnetic noise and its ability to distinguish the types and energies of individual particles, as illustrated here by detailed calibrations of its respo...

D3He-proton emission imaging for inertial-confinement-fusion experiments (invited)

Proton emission imaging cameras, in combination with proton spectrometers and a proton temporal diagnostic, provide a great deal of information about the spatial structure and time evolution of inertial-confinement fusion capsule implosions. When used with D3He-filled capsules, multiple proton emission imaging cameras measure the spatial distribution of fusion burn, with three-dimensional information about burn symmetry. Simultaneously, multiple spectrometers measure areal density as a function of angle around the imploded capsule. Experiments at the OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] have already proven the utility of this approach. An introduction to the hardware used for penumbral imaging, and algorithms used to create images of the burn region, are provided here along with simple scaling laws relating image resolution and signal-to-noise ratio to characteristics of the cameras and the burn region.

Proton core imaging of the nuclear burn in inertial confinement fusion implosions

A proton emission imaging system has been developed and used extensively to measure the nuclear burn regions in the cores of inertial confinement fusion implosions. Three imaging cameras, mounted to the 60-beam OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)], use the penetrating 14.7MeV protons produced from DHe3 fusion reactions to produce emission images of the nuclear burn spatial distribution. The technique relies on penumbral imaging, with different reconstruction algorithms for extracting the burn distributions of symmetric and asymmetric implosions. The hardware and design considerations required for the imaging cameras are described. Experimental data, analysis, and error analysis are presented for a representative symmetric implosion of a fuel capsule with a 17-μm-thick plastic shell and 18atm DHe3 gas fill. The radial burn profile was found to have characteristic radius Rburn, which we define as the radius containing half the DHe3 reactions, of 32±2μm (burn radii measure...

Capsule-areal-density asymmetries inferred from 14.7-MeV deuterium–helium protons in direct-drive OMEGA implosions

Capsule-areal-density (ρR) asymmetries are studied for direct-drive, spherical implosions on the OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Measurements of copious 14.7-MeV protons generated from D3He fusion reactions in the imploded capsules are used to determine ρR. As they pass through the plasma, these protons lose energy, and this energy loss reflects the areal density of the transited plasma. Up to 11 proton spectrometers simultaneously view D3He implosions on OMEGA from different directions. While the burn-averaged and spatially averaged ρR for each implosion is typically between 50 and 75 mg/cm2 for 20-μm plastic shells filled with 18 atm of D3He gas, significant differences often exist between the individual spectra, and inferred ρR on a given shot (as large as ∼±40% about the mean). A number of sources inherent in the direct-drive approach to capsule implosions can lead to these measured ρR asymmetries. For example, in some circumstances these asymmetries can be at...