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