Dry Wall Response to the HIB (close-coupled) IFE target

1. Dry Wall Response to the HIB (close-coupled) IFE target Presented by D. A. Haynes, Jr. for the staff of the Fusion Technology Institute University of Wisconsin

2. Summary/Outline The target output from the close-copled HIB target is substantially different from that of the direct-drive laser driven targets, in that its dominant non-neutronic threat component is from x-rays. Protecting the first wall from these x-rays requires more buffer gas than either SOMBRERO or the AU-coated NRL targets. • Comparison of threat spectra • First wall survival • Future work

3. Though the total yields of the SOMBRERO and high yield closely-coupled HIB targets are similar, the partitioning and spectra of the non-neutronic output differ significantly. • Over 25% of the yield from this target is in x-rays, compared with 5% of SOMBRERO’s, or 1% of the NRL Au-coated targets’.

4. X-ray Spectra • The x-ray spectrum of the HIB target is harder than that of the SOMBRERO, but not so hard as the NRL Au-coated target. • “Quantity has a certain quality all its own.” If our goal is to prevent vaporization in a 6.5m chamber, we must include a buffer gas at pressures above those required for SOMBRERO.

5. 6.5m Graphite chamber results: Chamber survives at 1000C, at 240mTorr, 1450C at 300mTorr • The gas density and equilibrium wall temperature have been varied to find the highest wall temperature that avoids vaporization at a given gas density. • Vaporization is defined as more than one mono-layer of mass loss from the surface per shot. • The use of Xe gas to absorb and re-emit target energy increases the allowable wall temperature substantially.

6. Surface Temperature and Temperature Profiles for 6.5m Graphite chamber, T_equilibrium=1000C The first peak in temperature is due to the prompt x-rays. The second is due to the re-radiation of the x-ray and ion energy by the Xe buffer gas.

7. The amount of Xe necessary to prevent wall vaporization for the 6.5m graphite chamber and the CC HIB target is also sufficient to stop all the ions except the knock-ons. Per shot accumulation: (240mTorr, 1000C T_eq.) D 6.698E+16 T 7.020E+16 P 5.596E+15 3He 7.592E+11 4He 2.515E+13 Does the accumulation of hydrogen and helium isotopes in the 1st mm of the wall at this rate pose a problem?

8. The x-ray deposition length in W is considerably shorter than that of C. To avoid first wall degradation, between 0.3 and 1 Torr of Xe is required to protect a W first wall at 6.5m from the CC HIB target, and a T_eq of 1000C.

9. Conclusion and future work • Xe density-T_equilibrium operating windows for the closely coupled HIB indirect drive target have been defined. • The large fraction of this targets yield in x-rays (115MJ) necessitates some form of first wall protection for a 6.5m C or W wall. • The amount of Xe required to protect the first wall from vaporization by x-rays is sufficient to stop all but the energetic knock-on ions. Is the accumulation of H and He isotopes in the first mm of the wall a problem? • Future work: • Finish write up of dry wall chamber physics work.