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Influence of Toroidal and Vertical Magnetic Fields on Ion Cyclotron Wall Conditioning in Tokamaks. Presented by A.Lyssoivan LPP-ERM/KMS, Brussels. With contribution from - PowerPoint PPT Presentation
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A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 1
ASDEX UpgradeERM-KMS
LPP
Influence of Toroidal and Vertical Magnetic Fields on Ion Cyclotron Wall Conditioning
in TokamaksPresented by A.Lyssoivan LPP-ERM/KMS, Brussels
With contribution fromG.Sergienko, V.Rohde, V.Philipps, G.Van Wassenhove, M.Vervier, V.Bobkov, J.Harhausen, R.Koch, J.-M.Noterdaeme, D.Van Eester, M.Freisinger, H.-U.Fahrbach, H.Reimer, A.Kreter, D.A.Hartmann, J.Hu, R.Weynants, O.Gruber, A.Herrmann, D.Douai, Y.D.Bae, H.G.Esser, J.G.Kwak, E.Lerche, O.Marchuk, V.Mertens, R.Neu, U.Samm, A.Scarabosio, C.Schulz, S.J.Wang,
TEXTOR Team and ASDEX Upgrade Team
A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 2
ASDEX UpgradeERM-KMS
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Outline
• Motivation
• ICRF Plasma / Antenna Coupling Characterization
• ICWC in TEXTOR and ASDEX Upgrade
• ICWC Extrapolation to ITER
• Conclusions
A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 3
ASDEX UpgradeERM-KMS
LPP
Motivation
ICRF discharge has a high potential for wall conditioning (tritium retention, surface isotope exchange, wall cleaning/coating) in the presence of permanent high magnetic field.
Ion Cyclotron Wall Conditioning (ICWC) was approved for integration into the ITER baseline using ITER ICRF heating system.
Further development of the ITER relevant ICWC scenarios with conventional ICRF antennas is an important and urgent task.
A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 4
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Plasma Production with Standard ICRF Antennas
TEXTORICRF antennas
f=25-38 MHz, BT=0.25-2.5 T, p=(1-10 )10-2 Pa
AUGICRF antennas
f=30.0; 36.5 MHz, BT=1.0-2.4 T, p=(1-8 )10-2 Pa
RF Field/Wavesexcitation
RF Powere-collisional absorption
Neutral Gase-collisional ionization
A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 5
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ICWC Optimization
ICRF Plasma Production Removal Mechanisms
AntennaCoupling
GRFplRF PP
PlasmaHomogeneity/ Extension
Fast IonsGeneration
1. High Ion Cyclotron Harmonics, =nci, n>>12. Mode Conversion, = ci
BT+BV, BV<<BTFundamental
Ion Cyclotron Resonance = ci
A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 6
ASDEX UpgradeERM-KMS
LPP
TEXTOR: ICRF Plasma Characterization
ICRF plasma can be produced at any BT-field
=10cH+ (BT0.2 T): High coupling (0.8), density (>21017 m-
3) and homogeneity
=cH+ (BT2.3 T): improved coupling (0.5) and homogeneity
ne, Te and Ppl vs BT
A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 7
ASDEX UpgradeERM-KMS
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AUG: ICRF Plasma Characterization
Mode conversion scenario in (He+H2)-plasmas:
Higher antenna coupling (up to 3 times)
Better homogeneity and extension in radial direction
Better performance at two frequencies
(He+H2)-plasma vs He-plasma
BT+BV vs BT
Vertical magnetic field improves plasma homogeneity in poloidal dirction and extends it towards divertor
He, f=30 MHz He+H2, f=30 MHz He+H2, f1=30 MHz+f2=36.5 MHz
I II III
BT BT
BV
BT=2.4 T, BV=0 BT=2.4 T, BV0.02 T
A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 8
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ICWC in TEXTOR(C-coated wall)
=10cH+ (BT0.2 T): Effective conditioning due to high antenna coupling and homogeneity possible in both, low and high the BT-fields
=cH+ (BT2.3 T): Mode conversion in (He+H2)-plasmas is the best scenario for ICWC (coupling + homogeneity + fast particles)
Applied BV-field (BV << BT) increased ICWC yield
Removal rate: spdtdpVtQRR )/(~)(
Measured removal rate for m=3 vs BT Calculated absorbed power vs BT
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.60
1
2
3
4
5
6
7TEXTOR- (He+H2)-plasma +Bv
- (He+H2)-plasma
- He-plasma
HD
Rem
oval
Rat
e[1
0
mol
/(skW
)]16
BT [ T
0
20
40
60
80
100
cH+ cH+
PePH+
cH+
Mode Conversion
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6BT [ T ]
TEXTOR
P abs/
spec
ies
/PR
F-t
see G.Sergienko, P2-45, 27/05/2008
A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 9
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ICWC in ASDEX Upgrade (W-coated wall)
Benefit from mode conversion in (He+H2)-mixture with ICR (=cH+) location closer to the antenna ICWC output correlates with fast particles energy and power absorbed by protons BV-field improves the ICWC effect Major concern – ICWC homogeneity (efficient cleaning from ~25% of the AUG surface)
Measured removal rate for m=40 vs BT Fast particles energy/power vs BT
0
1.0
2.0
3.0
4.0
5.0
1.6 1.8 2.0 2.42.2
Ar
Re
mo
val
Ra
te [
a.u
.]
AUG- ICWC in (He+H2) + Bv- ICWC in (He+H2)- He-DC
BT [T ]1.6 1.8 2.0 2.2 2.4
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
BT [T ]
0.1
0.2
0.3
AUG
P /P [ r.u.]H+ RF-totH-atom averaged energy[ keV ]
< E > experimentH
P / P modelRF-totH
experiment
modeling
A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 10
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ICWC Extrapolation to ITER:scenario for operation
0.32 m
row 1 & row 2: /3, f=40 MHzrow 3 & row 4: /6, f=48 MHz
12
34
TOMCAT modeling (rpl2.4 m, R0=6.2 m, BT=3.6 T, ne0=3x1017 m-3, Te0=5 eV):- Mode conversion in (He+H2)-plasmas at two frequencies
-2.5 -2.0 -1.5 -1.0 -0.5 0 0.5 1.0 1.5 2.0 2.50
0.2
0.4
0.6
0.8
1.0
r [m]
Abs
orbe
d po
wer
-per
-spe
cies
[a
.u.] ITER
cHe4+ cH+
f=40 MHzf=48 MHz
eHe4+H+
A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 11
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Modeling with 0-D plasma/transport code
1. 0-D Plasma/Transport code: ne(1-4)1017 m-3, Te~1.5 eV, ioniz=1-2%, p=(2-8)10-2 Pa PRF-pl (ITER)= 0.2-1.5 MW (coupl0.40) PRF-G (ITER)0.5-3.8 MW2. Extrapolation from TEXTOR data (assuming similar power density and
coupl0.40):PRF-pl (TEXTOR) 12-30 kW P RF-pl (ITER) 1.0-2.5 MW P RF-G (ITER) 2.5-6.0 MW
ICWC Extrapolation to ITER:power for operation
0
0.2
0.4
0.6
0.8
1.0
Ee-excitEe-ionizEe-rec
Ee-iEe-confEe-heat
ITER
Time [s]0 0.02 0.04 0.06 0.08 0.1
Ele
ctro
n E
nerg
y L
osse
s [
r.u.
]
excitE1234
2468
10
1012
1014
1016
1018
00.20.40.60.81.0
Time [s]0 0.02 0.04 0.06 0.08 0.1
TeTiTa
nei
0
ITER
nei
n [m ]e -3
P [MW]RF-e
i [%]
T [eV]
A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 12
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Conclusions
Inter-machine (TEXTOR, ASDEX Upgrade) ICWC studies:
Wall conditioning in the mode conversion scenario in the presence of toroidal and vertical magnetic fields (BV<<BT) may be considered as the most promising candidate for application in ITER using the main ICRF antenna. Better radial/poloidal homogeneity of the ICRF plasma and its ability to accelerate ions at the fundamental ICR may contribute to improving the conditioning effect.
ICWC at high cyclotron harmonics appears also to be attractive mainly due to very high antenna-plasma coupling (80%) and plasma homogeneity. However, the scenario needs operating at high generator frequencies for the nominal magnetic fields and does not produce fast ions.
Modeling with the 1-D RF and 0-D plasma codes and extrapolation from the existing machines give a good evidence for the feasibility of using ICWC in ITER with the ICRF heating system.