Solid DT Studies James K. Hoffer

1. LA-UR-02-1622 Solid DT Studies James K. Hoffer presented at the High Average Power Laser Review sponsored by The Department of Energy Offices of Fusion Energy Sciences & Defense Programs hosted by General Atomics San Diego, CA, April 4–5, 2002

2. Target Injection-1: Target Materials Response - LANL Overall Objective…………. Response of target materials to injection stresses FY 02 Deliverables……….. 1. Design of an experiment to determine the effect of a rapid temperature transient on a representative DT ice layer. 2. Start experiments to measure DT yield strength and modulus. 3. Measure solid DT surface spectrum following beta-layering over a layer of foam. 4. (new!!): Investigate slow “bounce freezing” of D2 in unmounted spherical capsules. Relevance of Deliverables [X] Energy……………… Needed for injection into hot chamber [X] NIF…………………… Research on materials in NIF targets HAPL @ GA Apr ‘02

3. Progress report: deliverable No. 1 The effect of a rapid temperature transient on a solid DT layer HAPL @ GA Apr ‘02

4. There are two major building blocks, the target and the heating method • There are two possible target geometries: • A cylindrical configuration to measure DT layer response • A spherical target filled & layered with solid DT • not really a surrogate at all, but an actual target! • results will vary depending on the exact target composition, foam, etc.  • There are several methods to induce rapid heating: • Direct heating of the solid DT layer • we have recently shown that direct heating of the DT layer, using a steady heat flux, is sufficient to simulate radiation from a hot chamber. • Direct heating of a shroud: • heating of a spherical or cylindrical shroud to high temperatures is difficult to do quickly and the temperature will be ramping. • Illumination of a cold spherical shroud or ‘integrating sphere’ to duplicate black-body radiation from a hot shroud: • easy to do quickly but difficult to match the IR spectrum • choice of window materials critical to IR spectrum on target   HAPL @ GA Apr ‘02

5. Direct heating of a DT-layer: Stycast epoxy Layering insert Heater winding Layering cell HAPL @ GA Apr ‘02

6. Simulations using prototype spherical targets can be carried out in the Cryogenic Pressure Loader (CPL) high pressure 4He line to operate the permeation cell breachlock seal 20,000 psi DT fill line breechlock and seal plug LVDT’s detect layering sphere position thermal shield, attached to the 60 K stage of the cryocooler permeation cell sparelow-pressure fill connection copper layering (hemi)sphere assembly cold plate 10 K stage of cryocooler HAPL @ GA Apr ‘02

7. Layering sphere assembly with prototype Omega direct drive target (1 mm-diameter), just below the permeation cell at the layering position HAPL @ GA Apr ‘02

8. However, we must modify the optical arrangement to permit an influx of infrared radiation, while still maintaining cryogenic conditions Option #1 – IR windows & shutters HAPL @ GA Apr ‘02

9. Among the several options we are considering, this is the leading candidate: Option #2 – IR fiber optics, introduced via plumbing ports HAPL @ GA Apr ‘02

10. Optical fibers can be used to pipe light entering the windows: Option #3 – IR fiber optics, collecting light introduced via the windows, but still requiring sets of shutters. HAPL @ GA Apr ‘02

11. Progress report: deliverable No. 2 Measurement of the strength of solid DT HAPL @ GA Apr ‘02

12. Our plan is to first grow a solid DT specimen with the aid of beta-layering: Camera resolution field: 2mm x 2mm 1024 x 1024 pixels, 12 bit dynamic range, DT edges determined to < 1 m. HAPL @ GA Apr ‘02

13. The stress-strain cell is dominated by the magnetostrictive strain actuator HAPL @ GA Apr ‘02

14. The smallest Energen, Inc actuator would result in a cell too long for our present optical apparatus: HAPL @ GA Apr ‘02

15. Energen, Inc. will supply a magnetostrictive actuator customized to our specifications: HAPL @ GA Apr ‘02

16. This permits mounting in our existing apparatus, without modifying the optical access ports. HAPL @ GA Apr ‘02

17. Further work is needed to insure a successful experiment: • Design of electrical feed-thrus into tritium cell • Actuator current leads • Piezo detector voltage leads • Design bellows to permit the 200-m gap between layering posts to be adjusted • Design flexible thermal linking of layering posts. • Evaluate power dissipation of Energen, Inc. actuator at steady state HAPL @ GA Apr ‘02

18. Progress report: deliverable No. 3 The effect of a foam shell on the surface roughness of the DT layer HAPL @ GA Apr ‘02

19. A foam-lined torus will permit clear optical observations of the DT layer: Empty torusside view(windows not shown) Filled with foam, bored out to yield a 75 micron-thick layer at the waist, then filled with liquid DT Filled with DT and beta-layered to yield a solid layer 100 microns thick. Using an offset foam bore, the thickness of DT above the foam varies. HAPL @ GA Apr ‘02

20. 2 mm tori have been fabricated from pure Pt: HAPL @ GA Apr ‘02

21. Meanwhile at Sandia, Diana Schroen, Inc. is busy adding the foam layers: HAPL @ GA Apr ‘02

22. If the DT surface is smoothed by the underlying foam layer, then further investigations at IFE scale would be appropriate. HAPL @ GA Apr ‘02

23. Progress report: deliverable No. 4 Bounce Freezing or “Sizzle Freezing” HAPL @ GA Apr ‘02

24. The goal is to freeze a spherical target slowly while being randomly tossed in a bounce pan, producing a uniform layer without the need of a further layering step. • Because we wish to maintain nearly continuous thermal contact and don’t need to bounce very high (cf: coating applications), the concept of ‘sizzle’ is more apropos. • Our Russian colleagues at LPI are willing to use their apparatus. • The apparatus is normally set up for ‘fall and strike’ layering. It is designed to handle unmounted cryogenic targets of millimeter size, filled with sufficient D2 to produce ~80 micron-thick solid layers. • It is unclear whether they need additional (financial) support. • It is unclear what financial support we can provide. • We may have to design and supply the bouncer platform and associated electronics. • Down the road, we can consider doing this experiment at Los Alamos in the CPL using tritium. HAPL @ GA Apr ‘02