April 9-10, 2003 HAPL Program Meeting, SNL, Albuquerque, N.M. 1 Lowering Target Initial Temperature to Enhance Target Survival Presented by A.R. Raffray Other Contributors: B. Christensen, Z. Dragojlovic, J. Pulsifer, M. S. Tillack, X. Wang UCSD D. Goodin, R. Petzoldt General Atomics HAPL Program Meeting Sandia National Laboratory, Albuquerque, N. M. April 9-10, 2003

HAPL Program Meeting, SNL, Albuquerque, N.M. 2 Target Survival During Injection Target heat source: energy exchange from chamber protective gas and radiation from chamber wall -Gas pressure up to ~50 mtorr at K (q cond ’’= W/cm 2 for Xe) -Chamber wall temperature ~ K (q rad ’’~ W/cm 2 ) -Total q’’ to be accommodated by target = W/cm 2 -q’’ to reach DT-TP for current target ~ 0.6 W/cm 2 Possible ways to increase thermal robustness of target: 1.Design modification to create more thermally robust target 2.Explore possibility of relaxing phase change constraint -Solution must accommodate target physics requirements 3.Possibility of injecting target at lower base temperature -Andy Schmitt's latest target calculations show no degradation in gain with no gas in the target center with target temperature down to 11.9 K ( 1- D runs) -Jim Hoffer and John Sheliak investigating how low the DT temperature could be decreased and still result in a smooth layer -Parametric analysis of allowable heat loads as a function of initial target temperature to assess benefit of operation with lower target temperature (focus of this presentation)

April 9-10, 2003 HAPL Program Meeting, SNL, Albuquerque, N.M. 3 Condensation from Xe as Background Gas (as a reminder of the target heat fluxes expected from Xe at different T and P) Note that radiation heating must be added to this to estimate the total heat load on the target

April 9-10, 2003 HAPL Program Meeting, SNL, Albuquerque, N.M. 4 Lowering Initial Target Temperature Significantly Delays DT- Foam in Reaching Triple Point q max ’’=1.2 W/cm 2 (e.g. for gas heating only: 1000K, 14 mtorr Xe or 4000 K, 5 mtorr Xe) (for radiation only: q max ’’= W/cm 2 from K wall at 6 m with 96% reflectivity) q max ’’=7.5 W/cm 2 (e.g. for gas heating only: 1000K, 100 mtorr Xe or 4000 K, 30 mtorr Xe)

April 9-10, 2003 HAPL Program Meeting, SNL, Albuquerque, N.M. 5 Lowering Initial Target Temperature Helps Accommodate Appreciably More Heat Flux Two time of flight example cases shown s and s For s case (e.g. for R=6 m and v=400 m/s) -For each degree decrease in initial target temperature from 18 K, the heat flux to reach the triple point increases by ~ 0.34 W/cm For example, q T-P ’’ increases from 0.6 W/cm 2 for an 18 K initial target temperature to ~2. 7 W/cm 2 for a 12 K initial target temp. -This certainly helps but needs to be supplemented by another measure to reach the ~10 W/cm 2 desired objective -Target design modification (e.g. insulating layer) -Allowing some level of phase change

April 9-10, 2003 HAPL Program Meeting, SNL, Albuquerque, N.M. 6 Combined Effect of Lower Initial Target Temperature and 150-  m Outer Insulating Foam Layer Allows Accommodation of q’’ > 10 W/cm 2 DT gas 1.5 mm DT solid 0.19 mm DT + foam x ~  m’s Dense plastic overcoat (not to scale) (0.289-x) mm Insulating foam Au or Pd Previous results from a target temp. of 18 K: -q’’ to reach T.P. = 7.5 W/cm 2 for a 152  m 10% dense foam layer

April 9-10, 2003 HAPL Program Meeting, SNL, Albuquerque, N.M. 7 DT Maximum Temperature History for Different Thicknesses (  m) of 25% Dense Outer Insulating Region for an Initial Target Temperature of 12 K For an outer foam region density of 25% (consistent with previous recommendation), a q’’ of 7.5 W/cm 2 can be accommodated with ~100  m outer foam thickness

April 9-10, 2003 HAPL Program Meeting, SNL, Albuquerque, N.M. 8 Summary of Thermal Analysis Results on Effect of Lowering Initial Target Temperature To increase target thermal robustness: -Maximize both thickness and porosity of outer foam layer, and -Minimize target initial temperature -while accommodating target physics and structural integrity requirements Foam Density Foam Thickness (  m) Target Initial Temp. (K) Maximum q’’ on Target (W/cm 2 ) Time for DTto Reach Triple Point (s) ~ ~ ~

April 9-10, 2003 HAPL Program Meeting, SNL, Albuquerque, N.M. 9 Conclusions Lowering the target initial temperature helps to substantially increase target thermal robustness –For a typical target at 18 K, the maximum q’’ for DT to reach its T.P. ~ 0.6 W/cm 2 –The maximum q’’ increases to 2.7 W/m 2 for an initial target temp. of 12 K However, additional measures are needed to reach q’’~ 10 W/cm 2 –Adding a foam insulating layer would help reach this goal e.g. for a 152  m 10% dense foam layer, q’’ = 7.5 W/cm 2 for an initial target temp. of 18 K and q’’ = 15.5 W/cm 2 for an initial target temp. of 15 K. a 110  m 25% dense foam layer, q’’ = 7.5 W/cm 2 for an initial target temp. of 12 K For increased target thermal robustness, it is preferable to have the maximum thickness and porosity outer foam layer, and the lowest target initial temperature which can still accommodate the target physics and structural integrity requirements. Allowing for phase change would relax the target thermal constraint and increase the target thermal robustness –An integrated thermo-mechanical model is being developed to help better understand the DT phase change process –Experimental validation will be required –Interaction among target physics, fabrication and survival analysis