NSTX-U Status of Liquid Metals – DEMO Workshop Meeting, Vienna, Austria – Dec. 17-20, 2013 1

Status of liquid metal plasma-facing component development

M.A. Jaworski, H. Ji, R. Kaita, R. Majeski, M. Ono,

J. Rhoads (PPPL), D. Ruzic (U-Illinois),

F.L. Tabares (CIEMAT), G. Mazzitelli (ENEA),

J.W. Coenen, B. Unterberg (FZJ), J. Hu (ASIPP),

T. Morgan, G. De Temmerman (FOM-DIFFER),

and S. Mirnov (SSC RF TRINITI)

NSTX-U Supported by

Culham Sci Ctr

York U

Chubu U

Fukui U

Hiroshima U

Hyogo U

Kyoto U

Kyushu U

Kyushu Tokai U

NIFS

Niigata U

U Tokyo

JAEA

Inst for Nucl Res, Kiev

Ioffe Inst

TRINITI

Chonbuk Natl U

NFRI

KAIST

POSTECH

Seoul Natl U

ASIPP

CIEMAT

FOM Inst DIFFER

ENEA, Frascati

CEA, Cadarache

IPP, Jülich

IPP, Garching

ASCR, Czech Rep

Coll of Wm & Mary

Columbia U

CompX

General Atomics

FIU

INL

Johns Hopkins U

LANL

LLNL

Lodestar

MIT

Lehigh U

Nova Photonics

Old Dominion

ORNL

PPPL

Princeton U

Purdue U

SNL

Think Tank, Inc.

UC Davis

UC Irvine

UCLA

UCSD

U Colorado

U Illinois

U Maryland

U Rochester

U Tennessee

U Tulsa

U Washington

U Wisconsin

X Science LLC

2nd IAEA DEMO Programme Workshop Vienna, Austria

17-20 December, 2013

NSTX-U Status of Liquid Metals – DEMO Workshop Meeting, Vienna, Austria – Dec. 17-20, 2013

Liquid metals offer potential advantages over solid

plasma-facing components (PFCs)

• Liquid metals provide a self-healing plasma-facing material

• Immune to thermo-mechanical stresses

• Returns to equilibrium after perturbations

• Replenishment eliminates net-reshaping by particle bombardment

• Separates neutron damage effects from plasma-material interactions

• Eliminates long-time constants associated with solid-wall material transport and evolution

2

Coenen, et al., JNM 2013

Arnoux, PFMC-14, Juelich

CMOD

JET

NSTX-U Status of Liquid Metals – DEMO Workshop Meeting, Vienna, Austria – Dec. 17-20, 2013

Two fundamental modes of operating are envisioned

for liquid metal PFCs: low and high recycling

• Low recycling expected with low-temperature (<400C) lithium surfaces

• Goal is to improve confinement well beyond conventional H-modes and reduce machine size

• May require fast-flow systems to maintain temperatures

• Low temperature limits will impact fusion power cycle

• High recycling surfaces expected with tin and high-temperature lithium surfaces

• Tin operation may look similar to tungsten surfaces, except immune to several damage mechanisms

• High-temperature lithium will ablate into the plasma possibly providing vapor-shielding and radiative cooling

• Maximum temperature limit dependence on evaporation rates and scrape-off layer pressure balance under investigation

3

NSTX-U Status of Liquid Metals – DEMO Workshop Meeting, Vienna, Austria – Dec. 17-20, 2013

Key research challenges before liquid-metal plasma-

facing components can be properly evaluated

• Topic 1: Stable operation of a free-surface, liquid-metal

on the first-wall and divertor of the fusion device

• Topic 2: Mass transport and material inventory control of

the liquid metal (and any absorbed materials e.g. tritium)

• Topic 3: Establishing the operating temperatures of the

liquid-metal PFCs consistent with good core performance

and efficient power extraction (i.e. an integrated scenario)

4

Jaworski PPCF 2013.

NSTX-U Status of Liquid Metals – DEMO Workshop Meeting, Vienna, Austria – Dec. 17-20, 2013

Research on liquid-metal PFCs is a worldwide effort

ranging from table-top devices to confinement exp.

• Numerous lab-scale devices have been created for examining fundamental aspects of liquid-metal PFCs

• E.g. Wetting experiments (ASIPP, U-Illinois, FZJ, PPPL, FOM-DIFFER)

• Linear plasma devices exposing test samples

• Magnum-PSI linear plasma device (Ne~5e20 m-3) (FOM-DIFFER)

• PSI-2 linear plasma device (Ne~1e19 m-3) (FZJ)

• Confinement devices

• Tokamaks and spherical tokamaks (EAST, HT-7, TEXTOR, FTU, T11-M, LTX, NSTX)

• Stellarators and reverse-field pinches (TJ-II, RFX)

5

NSTX-U Status of Liquid Metals – DEMO Workshop Meeting, Vienna, Austria – Dec. 17-20, 2013

Lithium Tokamak eXperiment (LTX) examining low-

recycling regime (PPPL)

• Small-scale, low-aspect ratio tokamak

• Conformal shells with evaporated lithium coatings

• Demonstrate strong pump-out with cold lithium coatings

• Find poor performance with coatings on hot-shells (T>180C) indicating contamination

• Motivates flowing and stirred liquid lithium to control impurities

6

Heating

Cooling

Integrated Scenarios

NSTX-U Status of Liquid Metals – DEMO Workshop Meeting, Vienna, Austria – Dec. 17-20, 2013

Liquid Metal eXperiment (LMX) examining fast-flow

MHD physics for possible fusion application (PPPL)

• MHD-channel flow experiment using Ga-In-Sn eutectic liquid metal

• Examining thermal transport at medium Reynolds and Interaction numbers

• Find strong alteration of thermal transport by vortex dynamics and reduced surface temperatures

7

LM Stability

Rhoads, JFM 2013; PPPL PhD Thesis 2013.

IR thermography of liquid

metal surface

NSTX-U Status of Liquid Metals – DEMO Workshop Meeting, Vienna, Austria – Dec. 17-20, 2013

NSTX demonstrated stable operation in divertor;

also observed surface contamination (PPPL)

• Liquid Lithium Divertor experiment demonstrated stable operation of capillary-system in divertor

• Oxygen contamination of surface consistent with little change in global performance

• Consistent with LTX results – working toward flowing liquid systems

8

LM Stability,

Material transport,

Integrated scenarios

Oxygen uptake by Li coating on Mo

LLD

Jaworski, NF 2013; Skinner, JNM 2013.

NSTX-U Status of Liquid Metals – DEMO Workshop Meeting, Vienna, Austria – Dec. 17-20, 2013

HT-7 and EAST advancing flowing liquid lithium

limiters (ASIPP)

• Demonstrated reduced hydrogen emission and impurity emission with lithium wall conditioning in EAST

• Fast recovery from vents may indicate unexpected benefit for reactor maintenance cycles

• Successfully tested several liquid-metal limiters on HT-7

• Developing limiter targets for testing on EAST, possibly this run-campaign

• Divertor targets being planned

9

LM Stability,

Material transport,

Integrated scenarios

HT-7 lithium

limiter

Recycling

reduction in EAST

NSTX-U Status of Liquid Metals – DEMO Workshop Meeting, Vienna, Austria – Dec. 17-20, 2013

Lithium Infused Trenches (LIMIT) concept being

tested on confinement devices (U-Illinois)

• Self-pumping system for refreshing surface and convecting heat

• Improved modeling of thermoelectric-MHD developed at U-Illinois

• Tested on HT-7

• Future tests planned on EAST, Magnum-PSI and others

10

LM Stability

Ruzic, NF 2011.

Fabricated

prototype

Hydrogen

outgassing

NSTX-U Status of Liquid Metals – DEMO Workshop Meeting, Vienna, Austria – Dec. 17-20, 2013

TJ-II stellarator now operating with liquid-lithium

limiter; examining hydrogen retention (CIEMAT)

• Upgraded from evaporator-based coatings to CPS-like limiter

• Deuterium retention experiments indicate little retained in limiter at 400C

• Large fraction removed at 375C

• Liquid lithium limiter survives deep insertion and biasing in TJ-II plasma

11

LM Stability,

Material transport,

Integrated Scenarios

Hydrogen

outgassing

TJ-II lithium

limiter

Tabares, IAEA 2012; Martin, FED sub.

NSTX-U Status of Liquid Metals – DEMO Workshop Meeting, Vienna, Austria – Dec. 17-20, 2013

FTU has upgraded to actively-cooled liquid lithium

limiter; examining Li radiative power exhaust (ENEA)

• New actively-cooled liquid lithium limiter installed for better temperature control

• Handles disruption loads without melt damage

• Stable vapor cloud formed in tokamak and radiates power

• But delicate balance required to avoid core collapse/disruption

• Plasma performance improved with lithium

• Lower Zeff, better confinement

12

LM Stability,

Material transport,

Integrated Scenarios

Lithium vapor cloud Apicella PPCF 2012.

Cooled Lithium Limiter

NSTX-U Status of Liquid Metals – DEMO Workshop Meeting, Vienna, Austria – Dec. 17-20, 2013

T11-M developing in-situ collection schemes to

control lithium inventory (TRINITI)

• Developed cryogenically cooled probe capable of collecting lithium

• Successfully demonstrated collection

• Inter-discharge glow discharge shown

• Lithium collection shown during discharges with collection probe in limiter shadow

• Deploying additional CPS devices in the machine

13

Material transport,

Integrated Scenarios

Lithium collected

vs. integral

pulse-length

Mirnov JNM 2013.

NSTX-U Status of Liquid Metals – DEMO Workshop Meeting, Vienna, Austria – Dec. 17-20, 2013

NSTX-U examining continuous vapor shielding and

radiative liquid lithium divertor concepts (PPPL)

• Gas cooling design studies indicate T>700C with 10MW/m2 incident heat flux

• Large lithium erosion into plasma could transition to vapor-shielded regime

• Experiments at Magnum-PSI demonstrate stable vapor-cloud over target

• Strong lithium injection and radiation basis of radiative liquid lithium divertor concept (M. Ono)

• Lithium introduced by evaporation/erosion in divertor

• Also introduced with pellet/granule and dust injectors further upstream

14

Material transport,

Integrated Scenarios

First Wall /

Blanket

At 500°C –

700°C

000000000000

Core

Reacting

Plasma

Edge

Plasma

Scrape Off

Layer

Flowing LLD

Tray

200 – 450 °C

Closed RLLD

LL Out LL In LL In

M. Ono, NF 2013; Jaworski, PPCF 2013.

NSTX-U Status of Liquid Metals – DEMO Workshop Meeting, Vienna, Austria – Dec. 17-20, 2013

Liquid tin tested in Magnum-PSI – observed droplet

emission and enhanced erosion (FOM-DIFFER)

• Performing experiments with tin-filled molybdenum mesh

• Observe droplet emission above critical temperature (500C)

• Evidence of tin vapor-shielding with reduction in deposited power vs. Mo reference sample

15

LM Stability,

Material transport

20 22 24 26 28 30 32

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

F

D

E

B

C

Mo, 0V

Mo, -30V

Sn, 0V

Sn, -30V

Re

move

d H

eat

(kJ)

Source Power (kW)

A

Tin in Molybdenum sample

Reduced

heat load

NSTX-U Status of Liquid Metals – DEMO Workshop Meeting, Vienna, Austria – Dec. 17-20, 2013

Liquid tin droplet emission also observed in

TEXTOR and PSI-2 (FZJ)

• Wetting and material compatibility studies performed with tin and gallium

• Tin filled tungsten of primary interest (stainless steels not compatible)

• Capillary mesh utilized to restrain fluid

• Exposures carried out in PSI-2 linear device

• Large erosion rates observed (>> sputter yield)

• Samples exposed to TEXTOR edge plasma

• Droplet emission also observed in TEXTOR edge plasma, under investigation

16

LM Stability,

Material transport,

Integrated Scenarios

See also: Coenen, PFMC 2013.

Tin in Tungsten sample

Droplet emission

NSTX-U Status of Liquid Metals – DEMO Workshop Meeting, Vienna, Austria – Dec. 17-20, 2013

Summary and outlook

• Liquid metal PFCs have attracted serious attention as an alternative material to tungsten

• Self-healing material is a key advantage for liquid metals

• Liquid metal PFCs can be grouped into two categories: low-recycling and high-recycling concepts

• Low-recycling research focuses on lithium exclusively

• High-recycling research includes tin and high-temp. Li

• Research on liquid-metal stability, material transport and development of integrated scenarios proceeding on a range of machines world-wide

• Positive indications are present for increased power exhaust capabilities with liquids and intrinsic impurity radiation

• Ultimate consistency with good core confinement still on-going research

17