Preheat Effects on Microballoon Laser-Fusion Implosions

Spatial evolution of wave amplitudes, stability of solutions, and bifurcations in sum and difference frequency generation processes under two-photon resonance conditions

“…5) Super-thermal electron preheat: The degree of energy deposition by long range super-thermal electrons is presently uncertain, and possibly negligible. Here we note only that [12] showed that only 4% energy deposition by super-thermals is sufficient for a <pR)> (and yield) degradation equal to that from the radiative preheat. 6) Energy absorption: From Fig.10c we see that a very slight adjustment in the assumed energy deposition can account for significant changes in the fuel temperature and neutron output.…”

“…This has little effect on the compressions achieved but it overestimates the fuel temperatures, so as to overstate the neutron yield of the KMS targets about 1.7-fold. 2) Radiative preheat: Multi-group photonics calculations with our non-equilibrium code show that reabsorbed line-and recombination radiation photons are reducing the ^p R^ achieved in the microballoon implosions by a factor of 2 to 3 [12]. This reduces the yield below the 3-T predictions an additional 2.5-fold.…”

“…The code does no super-thermal electron transport. It also does no line or recombination radiation transport, so it misses preheat effects that afflict pellets with high-Z ablators [12]. Furthermore, for computational speed in the many calculations, even the bremsstrahlung generation was suppressed (with A er set to zero in Ref.…”

“…When the T S =300 ps, e =16 J calculation is run on the non-equilibrium code [12], radiative preheat reduces p(0) by a factor of five to 24 g/cm 3 , and the maximum <(pR)> decreases to 1.6X10" 2 g/cm 2 . This implies a minimum mean shell radius of 6.7 A*m, which is consistent with the reported 10 2 -fold volume compression [4].…”

“…PROBLEM AREAS Fluorescence In Ref. [12], we showed that compression degrading radiative preheat should be substantially reduced by the use of a low-Z ablator layer. On the other hand, any opaque ablator material, such as beryllium is likely to encounter a non-negligible fluorescence problem, unless the overall laser system is most carefully designed.…”