Installation of a Plasmatron at the

Belgian Nuclear Research Centre and its use for

Plasma-Wall Interaction Studies

I. Uytdenhouwen, J. Schuurmans, M. Decréton, V. MassautSCK●CEN, Mol, Belgium

G. Van OostGhent University, Belgium

Key issues in PWI

Dedicated research facilities

Plasmatron facility VISION I

Conclusion

ITER

ITER like wallJET

(2 options)

PPCS (inspiration for DEMO)

W alloy

~ 540/720

He~ 600/990~ 540/720~ 540/720140/167Coolant I/O T(°C)

LiPbHeHeH2OCoolant

Armour material

SiCf/SiCW alloyW alloyCuCrZrStructural material

Model D or Self-cooled

Model C or Dual-Coola.

Model B or HCPB

Model A or WCLL

 Model ABor HCLL

TUNGSTEN

Plasma facing materials

Low Z, high oxygen gettering, good thermal conductivity, low solubility for hydrogen

Implantation with D, T (saturated very-near surface layers)

Beryllium

Radiation

Dilution

Loarte A. et al., NF 47 (2007)Causey R.A. et al., Fus. Eng. Des. 61 (2002)

BUT Nuclear reactions breed T, He in bulk High erosion yield

Low melting pointRES (radiation enhanced sublimation) ionized Be in the plasma deposition in divertor area mixed materials issue (alloy formation)

Mixed materials

Atomic percent Tungsten

0 10 20 30 40 50 60 70 80 90 100

Tem

pera

ture

(o

C)

1000

2000

3000

Weight percent Tungsten

0 70 80 90 100

Be W

34

22

o C

LIQUID

Be

12W Be

2W

<1750o C

<2250o C

12

87

o C

Be

22W

~952100 50o C

Stable Be-W alloys

Stable Be-W intermetallics are: ~2200°C (Be2W)

~1500°C (Be12W)

~1300°C (Be22W)

melting points closer to Be than to W!

Baldwin M. et al., J. Nucl. Mat. 363 (2007)

What happens if Be transport into the W bulk is rapid enough that alloy formation is not limited to the near surface?

Low Z (low central radiation, radiation in boundary)Good thermomechanical properties Lack of melting

Graphite

Causey R.A. et al., Fus. Eng. Des. 61 (2002)Shimomura Y., J. Nucl. Mat. 363 (2007)

BUT T retention issue

co-depositions (surface) depositions in gaps n damage (bulk)

Destruction by neutrons High erosion yield

CW

Low erosion yield + no formation like hydro-carbons low hydrogen retention (0.1 …1% instead of 40…100%)

High mass, low velocity of eroded particles ionization length << gyro radius 90% prompt redeposition

J. Roth et al., J. Nucl. Mat. 313-316 (2003)

Tungsten

LZ

BUT High radiative cooling rate

(compared to C)

Only limited concentration in plasma allowed (ppm range) Limit W erosion (transients, sputtering, …) High-Z impurity control by seeding with Ar, Ne

Tungsten

Sputtering yield by D negligible(100-1000 times smaller as for C)

Federici G. et al., J. Nucl. Mat. 313 (2003)

BUT Strongly dominated by

Low-Z intrinsic impurities Higher sputtering by Ar, Ne Mixed materials issue

(even if only one PFM)

Helium production Transmutation or plasma implantation May affect retention of T

Tungsten

Roth J. et al., 2nd EFDA workshop, Cadarache, Sept. 2007Ogordnikova O. et al.,

J. Nucl. Mat. 313 (2003)

T retention due to trapping in bulkInfluenced by: Damage sites

(n irradiation) Effective porosity

(manufacturing technique, existance of cracks, …)

Tritium retention

Kunz C. et al., J. Nucl. Mat. 367 (2007)

Tritium removal shemes(min. interference with plasma operation & performance) Heating in air or oxygen Laser heating flash lamps He-O glow discharges

Predictions needed for licensing Improvement in trapping/retention modelingneeds to be validated by experiments

Retention diagnostics needed

Minimize T inventory in the co-deposits (material choice, erosion limitation, …)

Other issues

Shimomura Y., J. Nucl. Mat. 363 (2007)

Degradation of in-vessel diagnostic components Dust Material deposition Erosion Neutron damage

Avoidance (material choice, …)

Limitation (removal methods, …)

Dust Major Safety issue for licensing (Be:toxic, C:tritium, W: active) Reaction with water leakage and H production (co-deposits) Reaction with air (vacuum leakage)

Dust generation/characteristics must be understood,

Diagnositcs needed (quantification),

In-situ removal methods

Key issues in PWI

Dedicated research facilities

Plasmatron facility VISION I

Conclusion

Synergistic effects: plasma steady-state fluxmaterial damage by neutrons tritium retentionmixed materials implications…

Key issues

Plasma simulators: reach high flux, low electron temperatures

H interaction studies:mainly by low flux, high energy ionsstandard particle accelerators, ion beam devices, tokamaks

BUT flux and energy influence the mechanism (retention, implantation, recycling)

Plasma simulators

SCK•CEN

Due to difficulties inherent to: transportcharacterization

of tritium, beryllium and neutron activated materials

It is advantageous to have devices (Plasmatron VISION I) in-house characterization tools

(tritium lab., beryllium cells, hot cells)knowledge and experience (BR2 matrix, fission, …)

at the same location

Beryllium cells

Tritium lab.

BR2 (high flux fission reactor)

Mechanical testing

Physico-chemical analysis

Microstructure characterization

Corrosion loops

Specimen preparation workshop

Hot cell capabilities

BR2

XPS

SEM

Mechanical

tests

TEM

Corrosion

Hot cells

Key issues in PWI

Dedicated research facilities

Plasmatron facility VISION I

Conclusion

ETHEL: the JRC experimental program (Ispra, Italy,1993)European Tritium Handling Experimental Laboratory

Shut down ten years agoDue to decommissioning of ETHEL buildings

Contract between SCK•CEN and JRC to transport plasmatronSeveral parts of equipment is missing

(were used for other projects)

Reinstallation at SCK•CEN for fusion applicationsRefurbishment/recovery will be done in 2008Most of technical documents were found in JRC archive

Background / History

New nameplasmatron VISION I

(Versatile Instrument for the Study of ION Interaction I)

Cold self-sustained volumetric plasmaVolume: 18 litres Target diameter: ~25cm Ion energies: 20 - 500 eVMagnetic field: 0.2T Pulse duration: steady stateFlux density target: ~ 1020-1021 ions/m2.s

Designed for PWI studies Installation for operation in glove boxA gas mixture with a certain D/T ratio can be created in a

volume by measuring the pressure and the mass flow of D/T coming from volumes containing D and T. Both loops have a separate control system.

Brief plasmatron facility description

Tominetti S. et al., Vuoto 26 (1997)

Plasma chamber

Gas, plasma, secondary ions and neutrals analyser

Gas inlet

CW

CW

CW

CW cooling water

TC

TC temperature control

I

I

I insulation

PM

PM

PM permanent magnets

T

T target

C CA

C cathode

A anode

UHV 1

UHV1 main pumping

UHV 3

UHV3 differential pumping

Sedano L. et al., Phys. Stat. Sol. 188 (2001)

Key issues in PWI

Dedicated research facilities

Plasmatron facility VISION I

Conclusion

Conclusion

Key issues determined by synergistic effects (steady state flux, transient loads, neutron damage)

Plasmatron VISION I can address several of these key issues because tritium beryllium neutron irradiated materialscan be studied under high flux densities, low plasma temperatures

PFM requirements for ITER/DEMO

• R&D programme: fabrication feasibility, resilience to neutron damage, activation, …

• BUT performance/use depends also on:T-retention, dust production, resilience to large steady-state fluences, transient loads, surface erosion, material redeposition

Thank you for your attention

Any questions?