March 3-4, 2005 HAPL meeting, NRL 1 Target Survival During Injection…The Advantages of Getting Rid of the Buffer Gas Presented by A.R. Raffray Other Contributors: K. Boehm, M. S. Tillack UCSD D. Goodin General Atomics HAPL Meeting NRL Washington, D.C. March 3-4, 2005

HAPL meeting, NRL 2 Benefit of Magnetic Diversion: No Protective Chamber Gas Needed and Much Reduced Heat Flux on Target During Injection Radiation heat flux becomes important Need good target surface reflectivity (we had estimated ~0.96 for a thin gold layer) For a reflectivity of 0.96 and a wall temperature of 1000K, q’’ rad on target is ~0.22 W/cm 2 IFE Chamber (R~6 m) No protective gas needed Chamber wall < 1000K, causing q’’ rad on target Target Injection Target Implosion Point

March 3-4, 2005 HAPL meeting, NRL 3 Although No Protective Chamber Gas is Needed, There Will Be Some Remnants of Reaction Products in Chamber DS2V runs for 0-10 mTorr of D 2 (higher heat flux for given density) Heat flux results shown for 1000K and 4000K D 2 and different target injection velocities assuming accommodation coefficient of 1 The exact value of the sticking coefficient is less important at low densities since shielding effects are much reduced Effects of any residual plasma not included

March 3-4, 2005 HAPL meeting, NRL 4 Combination of Initial Target Temperature and Injection Velocity (for a 6.5m chamber) That Would Result in DT Reaching its Triple Point for a Given Heat Flux Results can be used in combination with radiation and gas heating results to determine the right combination of parameters

March 3-4, 2005 HAPL meeting, NRL 5 Example Application of Parametric Results For a combination of T tgt =17 K and V inj =100 m/s, a q’’ of 0.5 W/cm 2 would result in DT reaching its triple point About 0.2 W/cm 2 of this q’’ is due to radiation for a 1000K wall and  =0.96 The remaining 0.3 W/cm 2 would allow ~ 4 mTorr of D 2 at 1000K and ~ 0.5 mTorr at 4000K

March 3-4, 2005 HAPL meeting, NRL 6 Integrated Plot to Show Combination of Target Initial Temperature and Injection Velocity to Reach DT Triple Point (19.79 K) for 6.5 m Chamber and 1 mTorr D 2 Total heat flux include energy exchange from 3.2x10 19 atoms/m 3 D 2 (~1 mTorr at RT) and a radiation heat flux of 0.2 W/cm 2 (based on 96% target surface reflectivity and 1000 K chamber wall temperature) Lower gas density and heat flux opens possibility of lower injection velocity (<~100 m/s) and simpler injection method (mechanical). Minimum velocity limited by having only one target in the chamber at a time(32.5 m/s for 6.5 m chamber and rep rate of 5)

March 3-4, 2005 HAPL meeting, NRL 7 Conclusions: Good news about magnetic diversion but prudence dictates continuation of our effort in better understanding target thermo-mechanical behavior including nucleation The absence of protective gas would greatly enhance target survival. This allows for lower injection velocity (~ m/s) and opens the door for different injection techniques (mechanical) However, lower velocity would require lower target temperature Uncertainty also in ions conditions during injection Still very important to better understand phase change behavior of target, in particular phase change and nucleation -Better assess survival margin for both the former base case and the new “lower velocity” case -Understanding and modeling of experimental results is needed (LANL has observed interesting bubble behavior including the effect of He-3) Thus, we are continuing our focus on target thermo-mechanics and nucleation modeling -Results from this will be reported at the next HAPL meeting