Vienna University of Technology (TU Wien)slides provided by F. Aumayr

EURATOM – ÖAW: Contribution of the Austrian Fusion Association

2006

Innsbruck University

W. Schustereder

Material Research DivisionMax-Planck-Institut für Plasmaphysik, EURATOM Association

85748 Garching, Germany

Vienna University of Technology (TU Wien)

Slow ion-surface interactions with relevance to fusion edge plasma

Innsbruck University

Sputtering and electron emission due to ion impact on plasma relevant surfaces (graphite, tungsten, ...)

Speciality: (slow) multiply charged ions (e.g. Cq+ up to q=6)Experimental techniques:

Sensitive quartz crystal micro-balance, AFM/STM

Electron emission: yield, statistics and energy distribution

Modelling of the plasma sheath potential in the presence of electron emission

Fragmentation and molecular reactions during atomic and molecular ion impact on surfaces + Sticking

plasma core

Zq+

neutralse-

ions

Z

divertor region

divertor plates first wall

plasma edge

ion - atom ion - molecule

collisions

ion - surface collisions

charge exchange excitation ionization

sputtering desorption

electron emission reflection

Z*(q-1)+q+

photon

Need of fundamental understanding of PWI processes

Well defined laboratory experiments

Specific modelling and extrapolation to ITER

n

0.0

0.5

1.0

1.5

2.0

2.5

0 20 40 60 80 100 120

(

e-/io

n)

v (104 m/s)

H3+

H2+

H+

Electron emission due to ion-impact on carbon and tungsten tiles

Electron emission and plasma sheath potential

Tore Supra carbon tile

0.0

0.5

1.0

1.5

2.0

102 103 104

elec

tro

n e

mis

sio

n y

ield

(e- /i

on

)

E(eV)

Heq+ W

He2+

He+

E/m (keV/amu)

0.1 1 5

Electron emission due to impact of singly/multiply charged carbon ions on carbon tiles

0

1

2

3

4

5

6

7

8

0 20 40 60 80 100 120

(

e-/io

n)

velocity (10 4 m/s)

Cq+ Graphite

C4+CL

C4+HOPG

C2+HOPG

C+HOPG

C5+CL

C2+CL

Electron emission and plasma sheath potential0

- 50

0 eV

in collaboration with in collaboration with S. Kuhn et al., Univ. InnsbruckS. Kuhn et al., Univ. Innsbruck

Sheath potential in front of an electron emitting wall

Modelling of the plasma sheath potential in the presence of electron emission

sheath model:in collaboration with

preliminary results:

without electron emission:   3kT

including electron emission:   2kT

N. Schupfer et al. Plasma Phys. Contr. Fusion,

(2006)

Total sputtering yields due to impact of singly and multiply charged ions

quartz-crystal

target (thin evaporated film)

Zq+

To,+,-

sensitivity: 0.5% monolayer per minutesensitivity: 0.5% monolayer per minutestability: 3mHz/min RMS noise at 6 MHz (f/f ≤ 10-9)

a-C:HWBe

WOx

BeOx

...

Research topic: Ion/surface collisions

Energy range of interest: ~ 1- 100 eV Low collision energy: enough energy to break molecular bonds, fragmentation

pattern is characteristic for both the projectile and the surface Projectiles:

Hydrogen molecules: H2+, H3

+, D2+, D3

+, HD+, HD2+

Hydrocarbons, i.e.: CD3+, C2H6

+, C2H4+, C2D6

+, C2D4+

small hydrocarbon molecules, present in most vacuum devices, therefore important for

modelling Plasma-wall interactions, break down graph for C2H6+ well known.

Surfaces:Stainless steel: data available, used for comparison Diamond surfaces: nanocristalline diamond on W-C bond with 6% Co;

terminal step in air or H-atmosphereBeryllium: first experimentsTungstenPlasma sprayed Tungsten (Collaboration with IPP Garching): ongoing

experiments Stainless steel with different surface coatings: Beryllium, Tungsten

in cooperation with D. Skalny (Bratislava)

Fragmentation and molecular reactions during (molecular) ion

impact on surfaces

• IBK

Fragmentation and molecular reactions during (molecular) ion

impact on surfaces

• IBK

Fragmentation and molecular reactions during (molecular) ion

impact on surfaces

20 30 40 50 60

0.1

1

10

100

H +

H +

2R

el. i

on s

igna

l (ar

b. u

nits

)

Collision energy (eV)

30 40 50 60 70

0.1

1

10

100

H+

H +

2

H +

3

Rel

. ion

sig

nal (

arb.

uni

ts)

Collision energy (eV)

20 30 40 50 60 70

1

10

100

D+

D +

2

Rel

. ion

sig

nal (

arb.

uni

ts)

Collision energy (eV)

20 30 40 50 60 70 80 90 100

0.1

1

10

100

D +

2

D+

D +

3

Rel

. ion

sig

nal (

arb.

uni

ts)

Collision energy (eV)

Fragmentation and molecular reactions during (molecular) ion

impact on surfaces

Fragmentation and molecular reactions during (molecular) ion

impact on surfaces

First fragmentation experiments on beryllium surfaces

600 800 1000 1200 1400 1600

Time of flight (nsec)

50 eV

Ion

Sign

al

11 eV

8 eV

5 eV

0 eVC2H+

6

Preliminary results:Higher impact energy required than for SS

Sticking coefficient of CD3+ on

plasma-sprayed tungsten (PSW) surfaces

0 20 40 60 80 1000,0

0,1

0,2

0,3

0,4

0,5

CD3

+ on PSW

CD3

+ on e.p. PSW

Stic

king

coe

ff.

S o

f de

uter

ium

Collision energy of CD3+ on PSW

W. Schustereder et al., NIMB, to be published

0 20 40 60 80 100

0

20

40

60

80

100

Collision Energy [eV]

Primary ion (CD3

+)

Exchange reaction products Sputtered ions

Rel

ativ

e ab

unda

nce

[%]

Hydrocarbon sticking properties on realistic surfaces

TW6-TPP-CNDSTICK

Outlook: PWI related tasks

• Chemical Erosion of C by D/H and other ions

• Erosion yield for higher hydro-carbons CxHy

• Erosion of redeposited layers (a-C:H layer) • Erosion Modelling• Effect of mixed layers: W, Be and C• Sputtering of W and Be

• Potential Sputtering of WOx and BeOx

• Electron emission studies• Modelling of sheath voltage• Fragmentation of molecular ions

• Sticking coefficients for hydro-carbons CxHy

Tragic message

† Prof. HP Winter 1941 - 2006