`` Solid DT Studies - Update presented by John Sheliak - GA Drew A. Geller, & James K. Hoffer - LANL presented at the 16th High Average Power Laser Workshop sponsored by The Department of Energy Defense Programs hosted by Princeton Plasma Physics Laboratory Princeton, NJ Dec 12-13, 2006 LA-UR

FY-’06 HAPL Uncompleted Milestones June July August September October November December January February March April May June 6/5/06 Relocation commenced 6/30/07 DT strength apparatus complete 12/31/06 Relocation completed

We have fielded an improved direct-heating cell Insertion of sapphire windows at the ends of the coil provides a clearer view through the solid DT layer and confines the material at the ends. The thickness of the internal windows was chosen to leave only small gaps at ends of the cell.

Target ‘lifetimes’ are now more than triple those measured in the previous unconfined cell X position error (mm) Target leaves conducting tube There is now no apparent displacement of solid ice along the cylindrical axis when the heater is energized. The 'lifetime’* of the ice layer is now appreciably (~3 X) longer than what we measured previously in the unconfined cell. 1 W/cm 2 and 19 K, we see no distortions for ~ 70 +/- 10 ms. –At 18 K, 'lifetime' is > 125 ms. –At 17 K, > 160 ms. –At 16 K, > 190 ms. The first 'event' we see now, even before we see a liquid layer form at the outer perimeter of the solid, is a 'crack' radially through the solid. This is probably a result of the whole ice layer starting to buckle from external pressure. * ‘lifetime’ for these measurements is defined as the 2 db point, or at the time of 25% roughening above the normalized initial layer roughness value, as measured at the inner DT solid layer edge

Solid DT layers showing 4 hr equilibrated layers at 16 K, 17 K, & 18 K, with later direct-heating effects 16 4 hrs + 0 ms 16 4 hrs ms 17 4 hrs + 0 ms18 4 hrs + 0 ms 17 4 hrs ms 18 4 hrs ms

Comparison of our current direct-heating data with previous data shows survival time more than tripling Direct heating with old cellDirect heating with newer improved cell

Solid DT layer thickness increases about 2% for new cell v.s. ~4% for old cell, over the survival period - at 18 K Direct heating with old cellDirect heating with newer improved cell

Comparison of current and previous experiments showing direct-heated roughening of 4 hr old layers Direct heating with old cellDirect heating with newer improved cell

Comparison of current and previous experiments showing direct-heated roughening of hr old layers Direct heating with old cellDirect heating with newer improved cell

Survival time is an inverse function of equilibration temperature: higher temperature = shorter survival Direct heating with old cellDirect heating with newer improved cell

Using 1 dB (12%) roughening as the survival benchmark lowers survival time, but not substantially Direct heating with old cellDirect heating with newer improved cell

Survival time is also an inverse function of equilibration time: longer equilibration time = shorter survival Direct heating with old cellDirect heating with newer improved cell

Update on DT strength cell construction It is not obvious here, but the upper Macor ® spacer is slightly canted and must be re- machined before the lower-layering-post assembly may proceed.

Update on DT strength cell construction (cont.): The cryostat for testing the functioning of the strength cell (operation of electro- strictive strain actuator, calibration of piezoelectric stress sensor, etc.) is nearly complete! During these tests, a simple spring will take the place of the upper layering post.

We are nearly ready to resume experiments at our new DT layering laboratory - early Jan 2007

Progress summary for solid DT studies Our most recent direct-heating experiments using an improved cell have shown survival time for solid DT layers to be more than 3x that of previous experiments ( ~90 19 K to K for 2 dB roughening benchmark) The cryostat for testing the functioning of the strength cell is nearly complete and nearly ready for calibration We have completed our laboratory relocation and set-up, with DT delivery expected by mid December; and new experiments beginning in early Jan 2007