Radomir Panek EU PWI Task Force Meeting - CEA Cadarache 1

PWI work in Association-IPP.CRPresented by R. Panek

Content:1. Collisions of hydrocarbon ions with carbon surfaces.2. Plasma spraying of tungsten. 3. Retention of tokamak atomic hydrogen in metalic membranes.

Radomir Panek EU PWI Task Force Meeting - CEA Cadarache 2

Collisions of hydrocarbon ions with surfaces* dissociations and chemical reactions from mass spectra, product ion translational energy and angular distributions

C1 ions: CH3+, CH4

+, CH5+

C2 ions: C2H2+, C2H3

+, C2H4+, C2H5

+

Influence of internal energy of projectiles on the extent of fragmentation*

Collisions of doubly-charged vs. singly charged ions with surfaces*(effect of charge: C7H8

+, C7H7+)

(* collaboration with the University of Innsbruck)

ENERGY RANGE

10 eV - 55 eV

SURFACE

Carbon: HOPG (highly oriented pyrolytic graphite), TOKAMAK tiles

SURFACE TEMPERATURE

- non-heated (room temperature)

- heated to 1000 K

Collisions of Hydrocarbon Ions with Carbon Surfaces

Z. Herman, J. Žabka, J. Roithová, J. Hrušák, J. Jašík, I. Ipolyi, L. FeketeováJ. Heyrovský Institute of Physical Chemistry, Acad. Sci.

Radomir Panek EU PWI Task Force Meeting - CEA Cadarache 3

Experiment Setup

PROCESSES OBSERVED

• neutralization of ions (survival probability)

• surface-induced dissociations (energy partitioning)

• chemical reactions at surfaces (H-atom, CHn-transfer)

• quasi-elastic scattering of projectiles

Radomir Panek EU PWI Task Force Meeting - CEA Cadarache 4

Percentage of Surviving Ions, Sa(%)

Radomir Panek EU PWI Task Force Meeting - CEA Cadarache 5

0 5 10 15 20 25 30 35

46.3eV

E'tr [eV]

31.3eV

20oC

600oC

C2H

3

+ + HOPG -> C2H

3

+

16.6eV

P[E

' tr]

0 5 10 15 20 25 30 35

Calculated from product C2H

3

+

46.3eV

E'tr [eV]

21.3eV

20oC

600oC

C2H

5

+ + HOPG -> C2H

5

+

11.6eV

P[E

' tr]

Product Ion Translation Energy Distributions

C2H3+, C2H5

+, HOPG, N=60o

Radomir Panek EU PWI Task Force Meeting - CEA Cadarache 6

Angular Distributions: Summary of C2Hn+

HEATEDNON HEATED

030

60

90

030

60

90

030

60

90

030

60

90

030

60

90

030

60

90

Radomir Panek EU PWI Task Force Meeting - CEA Cadarache 7

Summary

1. Heating to about 1000 K practically removes the hydrocarbon layer covering at room temperature the carbon surfaces

2. Ion survival probability Sa(%) for incident angle of Фn= 600

- about < 1% (0.1-0.5%) for radical ion projectiles (CH4+, C2H2

+, C2H4+)

- about 5-15 % for closed-shell projectile ions (CH5+, C2H3

+, C2H5+)

3. Inelasticity of dissociative collisions (dissociation after interaction with the surface):

translational energy of surface-energized projectile ions

- 30-40 % for non-heated (hydrocarbon covered ) surfaces

- 45-60 % for heated (clean) surfaces

Radomir Panek EU PWI Task Force Meeting - CEA Cadarache 8

Plasma Sprayed TungstenJ. Matejicek1, V. Weinzettl1, E. Dufkova1, V. Piffl1, V. Perina2

1 Institute of Plasma Physics, Prague, CZ2 Institute of Nuclear Physics, Prague, CZ

• Plasma spraying of tungsten Water- and hybrid-stabilized plasma torches Coating properties and optimization

• Testing in tokamak CASTOR Use of biasing to increase the power load

Radomir Panek EU PWI Task Force Meeting - CEA Cadarache 9

• Spraying optimization:– powder size selection– reduced oxidation– reduced porosity, increased thermal conductivity

• Spraying techniques:- water-stabilized plasma- hybrid-stabilized plasma (water+argon)- in air

• Reducing the oxidation:– Auto-shrouding: admixture of WC

decarburization of WC -> W2C -> WC reacts with oxygen, forms carbon oxide limits oxygen access to tungsten

– Very little oxide in the coatings (~0.3-0.5% surface, 0.05% inside)

Spraying development

Radomir Panek EU PWI Task Force Meeting - CEA Cadarache 10

Reducing the in-flight oxidation

pure W W+WC 5:1 pure W- lower plasma temperatures

- Ar stabilizes and elongates the arc- lower porosity- fewer unbonded interfaces- less oxide

Hybrid torch

Radomir Panek EU PWI Task Force Meeting - CEA Cadarache 11

Testing at tokamak CASTOR

Biasing electrode with a changeable head

a=85 mm

SOL

MOVABLE HOLDER

BIASING HEAD

Radomir Panek EU PWI Task Force Meeting - CEA Cadarache 12

• Surface morphology• Surface composition (EMPA,

RBS, ERDA)

• Plasma sprayed W• Plasma sprayed W+Cu (50:50 vol.)• Bulk W• Bulk Cu• Bulk graphite

Biasing head materials: Plasma sprayed W

Plasma sprayed W - detail

Testing at CASTOR (2)

Radomir Panek EU PWI Task Force Meeting - CEA Cadarache 13

Retention of tokamak atomic hydrogen in metalic membranes

M. Hron, J. Stöckel, F. Žáček, M. Notkin, V. Livshiths

Collaboration: Bonch-Bruyevich University, St.Petersburg

• Metalic membranes (Nb, V) absorb suprathermal atoms of hydrogen isotops that pass through an adsorbed layer on the membrane surface

• Absorbed atoms can move freely inside the membrane but the adsorbed layer hampers their exit

Principle

Radomir Panek EU PWI Task Force Meeting - CEA Cadarache 14

Hydrogen desorption from the membrane

Temporal evolution of the desorbed hydrogen pressure (membrane heated up to 1000oC during desorption)

Radomir Panek EU PWI Task Force Meeting - CEA Cadarache 15

Highest sensitivity to atomic hydrogen (relative to the background) was observed with the exposure temperature 400 K

H2 + Hmembraneexposed to plasma

H2

membraneexposed to neutral gas

Dependence of the desorption on membrane temperature during exposure

Hhydrogen atoms originating from plasma

Radomir Panek EU PWI Task Force Meeting - CEA Cadarache 16

Recent experiments have shown that in the tokamak conditions in CASTOR:

A/ membrane absorbs suprathermal hydrogen atoms

B/ number of absorbed atoms can be measured absolutely, so the neutral particle flux can be determined (calculation of particle balance?)

Conclusions