PISCES

AFOSR Materials and Processes Far From Equilibrium Workshop, Nov 2-4 2010 Arlington, VA.

Some PMI Research Activities of theUSDOE Fusion PFC Program

M. J. Baldwin University of California - San Diego

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Overview

• Brief description of the US-DOE PFC Program

• The UCSD PISCES PMI program.

• Examples of ‘far from equilibrium’ PMI observations on W

• Developing ties: An example of fruitful collaboration between Fusion and Propulsion PMI programs.

• Summary

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ITER: First Burning Plasma

Experiment• Large System

– (R~6m, a~2m)• Expensive (~6 G$)• 500 MW Fusion

Power• Energy Gain, Q=10

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Duration (s)

10-3 10-2 10-1 100 101 102 103 104 105 106 107 108

Hea

t flu

x (

MW

.m-2

)

0.1

110

100

1000

1000

0

Solar surface

Re-entryVehicles

FusionDivertor

FusionFirst Wall

RocketNozzles

FusionDisruptions

Fision FB

Fision LWR

FusionELMs

FusionVDEs

Plasma Facing Components (PFCs) must endure extreme conditions

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D, T, He plasma

ITER remote handling - divertor cassette mock-uphttp://www.alca-schio.com/nuclear_fusion_plants.htm

W, liner/dome

C strike points(start-up phase)W(DT phase)

Hot surfacesT ~ 600-1000 K

~ few % Ar, Ne ext. radiator

Be ‘rain’from FW erosion

ITER PMI is complicated

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PFC program supports ‘next step’

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PFC program members(Steering Committee)

Task: Guide work, priorities, budgets

Jeff Brooks (Purdue) – ChairmanGene Nardella, Barry Sullivan – DOEStan Milora – VLT

MembersD. Buchenauer (SNL) R. Nygren (SNL) R. Doerner (UCSD) A. Hassanein (Purdue)G. Tynan (UCSD) T. Rognlien (LLNL)D. Ruzic (UIUC) N. Morley (UCLA)R. Maingi (ORNL) M. Ulrickson (SNL)R. Majeski (PPPL)C. Wong (GA)D. Whyte (MIT)

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Major facility investment at UCSDPISCES-B: Be compatible PMI facility

Diagnostics• Probes, OES (absolute), YAG• In-situ XPS, AES, SIMS• Ex-situ SIMS, XPS, TDS, SEM, EDX,

WDS

PISCES-A: PMI & Supporting Research

CSDX: Supporting Research

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What do linear plasma devices offer?

• Toroidal PMI is complicated• Open field line geometry in

divertors can be simulated in linear plasma devices

• Steady state operation• Flexibility / control• Non toroidal geometry• Can be well diagnosed• PMI studies and code validation• Not limited to fusion PMI.

ITER PISCESVert. Targets

Target

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PISCES linear plasmas simulate ITER edge

PISCES ITER (edge)

Ion flux (cm2s–1) 1017–1019 ~1019

Ion energy (eV) 20–300 (bias) 10–300 (thermal)

Te (eV) 4–40 1–100

ne (cm–3) 1012–1013 ~1013

Imp. fraction (%) Several % Be or gas admix.

1–10 (ITER) Be

Pulse length (s) Steady state 300-500

PSI materials Any C, W, Be ..

Plasma species Any H, D, T, He

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The Boundary Region of the Plasma Is Where Plasma Physics & Materials

Science & Technology Meet • Plasma Will Contact w/ Material

Surfaces• How Do Material Surfaces Respond to

Plasma?• How Does Plasma Respond to

Materials?

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UCSD PISCES Program Research Focus

Perform Basic Plasma-Materials Interaction & Boundary Plasma Research Needed for ITER PFC Design Validation and Performance Predictions

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• Perform Controlled Be-C, Be-W, Be-C-W PMI Experiments• Steady-state & Transient Thermal Loads

• Make Related Edge/SOL Plasma Transport Studies• Develop and Validate Edge Plasma/PFC Models via

Collaborations• Mixed Mat’l Models (UCSD, EU)• Eroded Mat’l Transport (Argonne)• Time-averaged fluid codes (UEDGE, ERO,…)• SOL Main Plasma & Impurity Transport (UCSD)

Specifically …

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W far from equilib.: Example 1.

NAGDIS-II: He plasmaD. Nishijima et al. JNM (2004) 329-333 1029• Surface morphology • Shallow depth• Micro-scale

PISCES-A: D2-He plasmaM. Miyamoto et al. NF (2009) (in press)600 K, 1000 s, 2.0x1024 He+/m2, 55 eV He+

• Little morphology• Occasional blisters

(b) Under focused (c) Over focused

10nm

10nm

(a) Bright field image (under focused image)

PISCES-B: pure He plasma M.J. Baldwin et al, NF 48 3 (2008) 0350011200 K, 4290 s, 2x1026 He+/m2, 25 eV He+

NAGDIS-II: pure He plasmaN. Ohno et al., in IAEA-TM, Vienna, 20061250 K, 36000 s, 3.5x1027 He+/m2, 11 eV He+

100 nm (VPS W on C) (TEM)

~ 600 - 700 K > 2000 K~ 900 – 1900 K

• Surface morphology • Evolving surface• Nano-scale ‘fuzz’

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How does ‘fuzz’erode? W/ lower Y.

• Fuzz produced on W by He plasma exposure over 800 s at 1150 K, Ei ~ 90 eV.

• Switch to He/Ar plasma at t = 0 s, & measure time evolution of W I emission in front of W target.

• Ysmooth(Ar+W) ~0.05 @ Ei ~ 110 eV, by mass loss. (Agrees w/ TRIM).

• Yfuzzy= (0.05 / WI/ArII110 eV, smooth) x WI/ArII• Why is the sputtering yield reduced?

• Porosity? Internal bubble?• Not well understood.

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• Selected W samples exposed to the Magnetized Co-axial Plasma Gun (MCPG) at Univ. of Hyogo, Japan.

• Energy density: ~0.3-0.7 MJ/m2

• Pulse width: ~0.5 ms• Ion energy for D+: ~30 eV• ne ~1021 m-3, Gi ~ 1-2x1025 m-2 s-1

• Comparable to type I ELMs in ITER

How does fuzz take power loads?Initial tests encouraging.

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Ion fluence to surface varied before single ~45 MJ/m2 s1/2 laser pulse applied to W target

Vbias=125VG=2x1022/m2/sTe=11eVne=2x1024/m3

W far from equilib.: Example 2.

5x1022/m2

5x1023/m2

2x1024/m2

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Pathway for enhanced erosion

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 30 60 90 120 150Ion Energy [eV] (Bias-Float)

Ma

ss L

oss

(m

g)

Laser + Plasma

Laser Only

Plasma Only

G~ 1026 D+/m2

Tsurf ~ 50ºC

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Ties between plasma programs are mutually beneficial: Example 3.

• Enhanced high temperature erosion of Li by ion bombardment.Doerner, Baldwin et al. FED 61-62 (2002) 231.

• Also found for Be. At high temperature (Relevant to ITER).Doerner et al. JNM 1 (2005) 877.

• An ad-atom sublimation model explains the results.

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Enhanced erosion of BaO impregnated W cathodes by Xe.

0.001

0.01

0.1

1

10

300 400 500 600 700 800 900 1000

Ba loss rate during Xe plasma bombardmentBa evaporation loss rate

Surface temperature (C)

Eo

~ 6.3 eV

(BaO evap energy)

Ead

~ 1.7 eV

• Enhanced Ba loss is measured by biasing sample in Xe plasma

• At high temp., floating the material allows a direct measure of Ba sublimation.

• t measurements (3 points – 10 minutes) show no surface depletion of BaO

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The temp. dependent atom flux from a surface due to ion impact is:

)/(

adT) / (-EoopsTotal

adad

eff

o

exp1

J Y expnK YJJ

=

1

J Y =J

TE

plpl

rec

sub

pl

A

tt

Where Eeff = Ead - ED

Ead is the adatom binding energy to the surfaceED is the activation energy for surface diffusion of an adatomYad can be calculated with molecular dynamics codeA is a material constant

Independent of T

Independent of Jpl Dependent on both

Jpl and T

)/(

)/(

ad

expexp

1

J Y

TErec

TEsub

pl

D

ad

kk

)/(

adeffexpJ Y TE

plA

if adatomrecombinationdominates

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Ad-atom model (UCSD data)and prediction for thruster cathode.

1012

1013

1014

1015

1016

1017

1018

1019

300 400 500 600 700 800 900 1000

BaO loss rate & model 6-7-4 dataUCSD plasma etcher conditions

Sputt fluxEvap fluxAdatom fluxtotal fluxscaled data

Temperature (C)

30 eV ion energy

6e17 ions/cm2s

1012

1013

1014

1015

1016

1017

1018

300 400 500 600 700 800 900 1000

thruster sputtEvap fluxThruster adatomThruster total

Temperature (C)

30 eV ion energy

2e16 ions/cm2s

Thruster cathode conditions

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Summary• Substantial capital investment by US-DOE in fusion PMI

research and expertise spanning decades.• There are 9 active PFC research groups incl. PISCES

• PMI studies• PMI modeling / theory• Technology

• Opportunities for developing ties and collaborations are welcome.