Solid DT Studies James K. Hoffer

DOE OFES/DP

This work was performed under the auspices of the U. S. Department of Energy by the Los Alamos National Laboratory under contract No. W-7405-Eng-36. Materials Science and Technology

Solid DT Studies James K. Hoffer

presented at the

High Average Power Laser Reviewsponsored by

The Department of Energy Offices of Fusion Energy Sciences &

Defense Programshosted by

General AtomicsSan Diego, CA, April 4–5, 2002

LA-UR-02-1622

HAPL @ GA Apr ‘02 DOE OFES/DP

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

Target Injection-1: Target Materials Response - LANL


Progress report: deliverable No. 1

The effect of a rapid temperature transient on a solid DT layer


• 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

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.


Direct heating of a DT-layer:

Layering cell

Layering insert Heater winding

Stycast epoxy


permeation cell

sparelow-pressure fill connection

copper layering (hemi)sphere

assembly

cold plate

10 K stage of cryocooler

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

Simulations using prototype spherical targets can be carried out in the

Cryogenic Pressure Loader (CPL)


Layering sphere assembly with prototype Omega direct drive target (1 mm-diameter), just below the

permeation cell at the layering position


However, we must modify the optical arrangement to permit an influx of infrared radiation, while still

maintaining cryogenic conditions

Option #1 – IR windows & shutters


Among the several options we are considering, this is the leading candidate:

Option #2 – IR fiber optics,introduced via plumbing ports


Optical fibers can be used to pipe light entering the windows:

Option #3 – IR fiber optics, collectinglight introduced via the windows, but still requiring sets of shutters.



Measurement of the strength of solid DT


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.


The stress-strain cell is dominated by the magnetostrictive strain actuator


The smallest Energen, Inc actuator would result in a cell too long for our present optical apparatus:


Energen, Inc. will supply a magnetostrictive actuator customized to our specifications:


This permits mounting in our existing apparatus, without modifying the optical access ports.


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- gap between layering posts to be adjusted

• Design flexible thermal linking of layering posts.

• Evaluate power dissipation of Energen, Inc. actuator at steady state


The effect of a foam shell on the surface roughness of the DT layer



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.


2 mm tori have been fabricated from pure Pt:


Meanwhile at Sandia, Diana Schroen, Inc. is busy adding the foam layers:


If the DT surface is smoothed by the underlying foam layer, then further investigations at

IFE scale would be appropriate.


Bounce Freezingor

“Sizzle Freezing”



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.

Solid DT Studies James K. Hoffer

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