doe dp this work was performed under the auspices of the u. s. department of energy by the los...

DOE 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.

ESA-TSE Engineering Sciences and Applications DivisionTritium Science & Engineering

Solid DT Studies

James K. Hoffer, John D. Sheliak, & Drew A. Geller

presented at the

High Average Power Laser Reviewsponsored by

The Department of Energy Defense Programs

hosted by the

Naval Research Laboratory

Washington DC, December 5-6, 2002

LA-UR-02-7258

HAPL @ NRL Dec ‘02

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. Design apparatus to measure DT yield strength

and modulus.3. Measure solid DT surface spectrum following beta-layering over a layer of foam.

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


A new beta-layering cell has been designed and fabricated.

– We have added internal thermometry to the design.

– We are modeling this geometry to determine the amount of heat actually flowing into the solid DT.

– The heater insert has become substantially larger just to accommodate the thermometer

• Lakeshore Cernox bare chip: (.75 mm x .4mm x 1 mm long)

4.00 mm Ø

1 mm Ø

8.00 mm Ø


The thermometers were too big to fit!

• We had been informed that the leads were attached to the long ends of the element. They were, but in the wrong orientation!

• We had the precision shop use a small end-mill to widen the hole in the heater sleeve.

• The thermometer will be potted in epoxy after the heater winding is added.


The new camera is ready to follow the action at speeds up to 250 frames/second.

Here we show the new cell being rotated.

Rapid heating cell shown with front lighting


We are building a simple heater winding insert to heat the solid DT layer.

• The shape of the winding influences the shape of the resulting beta-layer, so it must be highly symmetric.

• Priorities of the LANL HEDP program have seriously impeded our access to the high precision machine shop.

• Nevertheless, the mandrels have been machined and the first heater winding has been wound:


We have added a new colleague to expedite our experiments. He has begun to carry out a

thermal analysis of the heater cell dynamics.

Drew A. Geller

Education

2000 Ph.D. in Physics, Cornell University Dissertation: The Field Dependence of Catastrophic Relaxation in Superfluid 3He-B Dissertation advisor: David M. Lee

1994 M.S. in Physics, Cornell University1991 B.A. in Physics, Columbia University

Professional Experience

2002-present Postdoc, ESA-TSE, Los Alamos National Laboratory, supervised by Jim Hoffer Project: Studies of beta-layering in tritium

2000-2002 Postdoctoral Fellow, MST-10, Los Alamos National Laboratory, supervised by Greg Swift Project: Development of thermoacoustic separation of gas mixtures

1992-2000 Graduate Research Assistant, Cornell University Projects: NMR and acoustics in superfluid 3He

1991-1992 Teaching Assistant, Cornell University

Research Interests

Physical acoustics, thermodynamics, separation science, and low temperature physics.



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.


Energen, Inc. has supplied a magnetostrictive actuator customized to our specifications:

1.767”

0.182”


The design is essentially complete. A set of check prints is being prepared:

MI TUTOYO HEAD P/N 148-205

ROTATED 90°

ROTATED 90°

ROTATED 45°

.0884 SETUP START

STRENGTH CELL ASSEMBLY

WI NDOW ASSEMBLY

MI CRO ADJ USTMENT ASSEMBLY

ROTATED 45°

BOTTOM POST ASSEMBLY

TOP POST ASSEMBLY

TOP SEAL CAP

BOTTOM BASE PLATE

COLD PLATE

THERMAL CONTACT A SSEMBLY (ROTATED 90°)

DT I NTRODUCTI ON ASSEMBLY


Power dissipation will not be low, as we first had been informed:


We are working out the last details of the strength cell:

• Power dissipation of the Energen, Inc. actuator at steady state will be too high to allow for adjustment of the gap.

• Hence we have designed a stage to permit the 200- gap between layering posts to be adjusted.

C

C B

304

301

302

305

306

B

307


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



There are several hypotheses concerning the effects of an intermediate foam layer on the inner solid DT layer

• Beneficial effects: – A smoother interior surface

• Because of the fine cell structure of the foam, freezing should begin with the formation of many small, randomly-oriented crystallites. These crystallites should propagate into the pure DT solid layer, hence there should be no tendency to form large crystalline facets at the solid-vapor boundary.

– Supercooling of the liquid should not occur• With millions of nucleation sites presented by the foam, the liquid will not supercool as is

observed in smooth plastic spheres without a foam layer.

• Detrimental effects:– If irregular, the overall shape of the foam may affect the shape of the solid DT.

• But I’m guessing that the gross shape of the foam will not influence the shape of the solid DT layer, because the foam is a thermal insulator and will not disturb the isotherms defined by the isothermal boundary (i.e., the metallic cell boundary in my cylindrical experiments or the ‘layering sphere’ utilized for spherical targets at Omega.)

– The polymeric foam material may be damaged by beta activity and decompose.– DT voids in the foam cells may become trapped

• The solid DT is 12.5% denser than liquid. A void space (full of DT vapor) therefore develops whenever a cell full of liquid is frozen. (When symmetrized by beta-layering, the void in a single spherical shell will extend exactly half-way across the cell.) Voids first formed in the foam cells tend to propagate inwards to the central vapor space. If the inner edge of a foam cell is blocked by a cell wall (i.e., if the foam is not completely ‘open-celled’), then the void may get ‘stuck’. Stuck voids may not be too detrimental, because they are sub-micron in size. But a secondary effect might be a very slow approach to equilibrium wrt the DT layer thickness.


A foam-lined torus will permit clear optical observations of the DT layer:

Empty torusside view

(windows not shown)

Filled with foam 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.

2.00 mm 1.85 mm

.025 mm


2 mm tori have been fabricated from pure Pt:


At Sandia, Diana Schroen & co-workers added ~70--thick foam layers to four tori:


The filled tori all have noticeable defects in the foam layers

Foam Cell ‘B’ Foam Cell ‘C’ Foam Cell ‘D’

Back lighting

Front lighting


We measured the foam thickness by ‘subtracting’ an image of the unfilled Pt torus. We then chose cell ‘C’ based on:

Cell ‘B’ - average d = 125µm

• overall symmetry, • average foam layer thickness, and • relative lack of defects at the toroidal waist

Cell ‘C’ - average d = 66µm Cell ‘D’ - average d = 47µm


Following beta-layering, we can show the pure DT layer by subtracting the empty foam image.

empty foam 75 µm DT layer (total)~30 µm is ‘pure’, while the

rest resides in the foam

Empty foam – DT Layer

Note that the solid DT ignores the defects in the foam!!!


The equilibration time is somewhat longer than we have experienced in foam-free cells


But the solid DT surface is much smoother than we have observed in this geometry


The mode 2 amplitude is responsible for a large fraction of the total rms roughness. Some of this is due to the fact

that we now cannot line up the empty torus ‘on axis’.


By plotting a ‘reverse sum’ of modes, the modal spectrum can be seen. The presence of the foam is dramatically

reducing the roughness power at l-modes above ~8.


This compares the ‘best’ of our previous results with our best result in foam. Simply put,

we have never seen such a smooth beta-layer!!


This compares the previous graph with the best of the LLNL data in spheres, where the solid DT layer

is grown as a ‘single crystal.’


As a function of time, we notice that l-modes 3 to ~8 equilibrate in the first 6 hours, followed by

all higher modes (up to ~100) during the next 12 hours.


This ‘disappearance’ of the mid and higher modes is precisely what we do not observe

when no intermediate foam layer is present.


During the course of the first month of experiments, we noticed that the foam layer thickness diminished.

However, the foam now appears to be stable.

Foam 100902, avg d = 66 µm Foam 101502, avg d = 57 µm Foam 102302, avg d = 51 µm

Foam 102802, avg d = 53 µm Foam 110402, avg d = 45 µmFoam 110102, avg d = 47 µm


It is possible to measure the surface roughness of DT beta-layered onto a true spherical surface,

using only flat optics:52

2.0

0 m

m

1.6

0

doe dp this work was performed under the auspices of the u. s. department of energy by the los...

Documents

pure dt solid layer

solid dt specimen

layer of foam

dt layer progress report

solid dt surface spectrum

representative dt ice

new cell

dt yield strength