`` Solid DT Studies - Update presented by John Sheliak - General Atomics Drew A. Geller, & James K. Hoffer - LANL presented at the 18th High Average Power Laser Workshop sponsored by The Department of Energy Defense Programs hosted by Los Alamos National Laboratory Santa Fe, NM April 8-9, 2008 LA-UR

Updated features of the most recent work We reported our initial results for thermal oscillation studies in a 2 mm i.d. Be torus, as well as work with solid layering in RF foam, at the Oct ‘07 HAPL meeting Since then, we performed additional data analyses for the thermal oscillation smoothing experiments, including data at 17.3, 18.0, 19.0, and 19.2 K We also performed several additional experiments with solid DT in an RF foam-layered sapphire sphere-cylinder - to augment the RF foam work reported at the October meeting

Initial results for thermal oscillation smoothing in the Be torus were reported at the Oct ‘07 HAPL meeting  Thermal oscillation experiments in our current sphere-cylinder cells have been hampered by dense clouds of DT and 3 He bubbles that obscure sections of the DT solid layer. Consequently, this bubble ‘noise’ makes accurate surface roughness measurements difficult.  In previous layering experiments, we used a 2 mm beryllium torus to study the effects of aging on DT layers  DT and 3 He bubbles are not visible in the Be torus because the ice layer is not transparent!  Thus, this was an interesting geometry in which to study the rms smoothing effect of temperature oscillations. Typical image with an ice layer with a thickness of ~ 100  m. (2 mm i.d. Be torus)

Surface roughness evolution, and reverse sum spectrum data were averaged for 18.3 K X position error (mm) Target leaves conducting tube Since there were no solid layer bubble distortions to hamper analyses, these results were encouraging; and thermal oscillations resulted in significant smoothing of equilibrated layers that began with a nominal initial roughness (i.e. typical layer roughness for this cell at these temperatures). Moreover, spectrum results are consistent with unobstructed (removing obscured layer sections from the analyses) layer data for the 2 mm Cu sphylinder.

Update of results for thermal oscillation studies Thermal oscillation smoothing of DT solid layers in the 2 mm i.d. Be torus

Thermal oscillation experiments were performed at 17.3, 18.0, 18.3, & 19.0 K… HAPL Draft Specs: ± 5mm (± 20mm ® -7% in gain); < 0.5µm for l ≥ 10 † NIF Specs: 0.92 µm overall, and 0.41 µm RMS for modes * † J.Perkins HAPL Direct Drive Target : Draft Laser/Target Specs – Nov ‘05, HAPL 8/8/2006 (uses NIF indirect drive specs for 2 mm targets and inner ice l ≥ 10) * J. Atherton et al. DT Layering and Characterization Update - LLNL

Solid layers ranged in thickness from 117 µm to 218 µm for 17.3 K oscillation experiments *19.2 K data was equilibration only - no oscillations were performed DT solid layer thickness tended toward thicker layers at 17.3 K, so that relevant HAPL 2 mm target layers were observed *

Averaged reverse sum spectra for the 17.3 K and 18.3 K thermal oscillation experiments Average spectra for 17.3 K and 18.3 K oscillation experiments show that low- & mid-mode smoothing are better at 18.3 K

Thermal oscillation smoothing of DT solid layers (con’d).. Our best overall RMS and mode spectrum data for 17.3 K & 18.3 K oscillation experiments

Best thermal oscillation smoothing of DT solid layer at 17.3 K 9.0 hrsThermal 1.6 hrsThermal 2.0 hrs ∆T = 0.5 K∂t = 2.5 min

The solid DT surface roughness at 17.3 K, shown as overall RMS as well as mode spectrum evolution Our best 17.3 K experiment included an initial 9 hr equilibration followed by 1.6 hrs of temperature oscillations, and a final 2 hrs of 17.3 K ‘relaxation’ to look for any re-roughening that may occur

Best thermal oscillation smoothing of DT solid layer at 18.3 K 8.3 hrsThermal 1.6 hrsThermal 2.0 hrs ∆T = 0.5 K∂t = 2.5 min

The solid DT surface roughness at 18.3 K, shown as overall RMS as well as mode spectrum evolution Our best 18.3 K experiment included an initial 8.3 hr equilibration followed by 1.6 hrs of temperature oscillations, and a final 2 hrs of 18.3 K ‘relaxation’ to look for any re-roughening that may occur

Results from 18.3 K oscillation experiments compare favorably with the NIF ignition spectrum HAPL Draft Specs: ± 5mm (± 20mm ® -7% in gain); <0.5mm for l ≥ 10 † NIF Specs: 0.92 µm overall, and 0.41 µm RMS for modes * † J.Perkins HAPL Direct Drive Target : Draft Laser/Target Specs – Nov ‘05, HAPL 8/8/2006 (uses NIF indirect drive specs for 2 mm targets and inner ice l ≥ 10) * J. Atherton et al. DT Layering and Characterization Update - LLNL

Update on results for RF foam Studies DT solid layers in RF foam inside a 4 mm sapphire sphylinder

Several additional experiments were performed with DT solid layers in RF foam Extend freeze (2.3 hrs); lower T to 17.3 K (28 min); and extend equilibration time (48 hrs) at 17.3 K Extend freeze (6.3 hrs) and equilibration (16 hrs) at 19.0 K Extend freeze (4.65 hrs); shorten equilibration (4 19 K); extend oscillation (4.5 hrs) and relaxation(4hrs following oscillations) Fast freeze (5 min) to 18.3 K; warm to liquid (10 min) then re-freeze to 19.0 K (4.2 min); Shorten equilibration (4 hrs); and extend oscillation (4.5 hrs) and relaxation (8 hrs following oscillations). Fast freeze (10 min) and extended equilibration (120 hrs) at 19.0 K; followed by thermal oscillations for 1.3 hrs

No significant change in bubble production was observed by varying freeze, equilibration, oscillation, and relaxation times Movie of 3 min freeze to 18.3 K, 10 min warm to liquid; 4.65 hr freeze; 19 K equilibration; 4.5 hr oscillation ;4 hr relaxation Movie of 5 min freeze to 18.3 K; 5 min warm to liquid; 4.25 min freeze to 19.0 K; 4 hr equilibration; 4.5 hr oscillation; 8 hr relaxation Ex 5-1Ex 5-2

We observed no significant reduction in bubble production, even with an extended equilibration of 120 hrs Movie of 10 min freeze to 19.0 K; 120 hr equilibration; 1.3 hr oscillation Ex 6

Progress summary update for solid DT studies Results for solid DT thermal oscillation smoothing inside a 2 mm Be torus, showed an overall RMS surface roughness reduction of about 23% at 17.3 K, and 30% at 19.0 K during oscillations Roughness spectra show that smoothing occurs primarily in the mid-modes, although in some low-modes as well; and that spectral roughness compares favorably with the current NIF standard ignition spectrum We observed no re-roughening of the solid layers during a 2 hr ‘relaxation’ period following the thermal oscillations Additional experiments with extended DT freeze, equilibration, oscillation, and relaxation times, showed no significant change in bubble production Varying the DT freeze procedure - fast freeze; warm to liquid; refreeze - showed no significant change in bubble production