A'Lyssoivan 18PSI, Toledo, Spain 27052008

1
Influence of Toroidal and Vertical Magnetic
Fields on Ion Cyclotron Wall Conditioningin
Tokamaks
Presented by A.Lyssoivan LPP-ERM/KMS, Brussels
With contribution from G.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
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Outline

• Motivation
• ICRF Plasma / Antenna Coupling Characterization
• ICWC in TEXTOR and ASDEX Upgrade
• ICWC Extrapolation to ITER
• Conclusions

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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.

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Plasma Production with Standard ICRF Antennas
RF Field/Waves excitation
RF Power e-collisional absorption
Neutral Gas e-collisional ionization
TEXTOR ICRF antennas
AUG ICRF antennas
f30.0 36.5 MHz, BT1.0-2.4 T, p(1-8 )?10-2 Pa
f25-38 MHz, BT0.25-2.5 T, p(1-10 )?10-2 Pa
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ICWC Optimization
ICRF Plasma Production
Removal Mechanisms
Antenna Coupling
Plasma Homogeneity / Extension
Fast Ions Generation
1. High Ion Cyclotron Harmonics, ? n?ci,
ngtgt1 2. Mode Conversion, ? ?ci
BTBV, BVltltBT
Fundamental Ion Cyclotron Resonance ? ?ci
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TEXTOR ICRF Plasma Characterization
ne, Te and Ppl vs BT

• ICRF plasma can be produced at any BT-field
• ?10?cH (BT?0.2 T) High coupling (??0.8),
  density (gt2?1017 m-3) and homogeneity
• ??cH (BT?2.3 T) improved coupling (??0.5) and
  homogeneity

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AUG ICRF Plasma Characterization
(HeH2)-plasma vs He-plasma

• Mode conversion scenario in (HeH2)-plasmas
• Higher antenna coupling (up to 3 times)
• Better homogeneity and extension in radial
  direction
• Better performance at two frequencies

He, f30 MHz
HeH2, f30 MHz
HeH2, f130 MHzf236.5 MHz
BTBV vs BT
Vertical magnetic field improves plasma
homogeneity in poloidal dirction and extends it
towards divertor
BV
BT
BT
BT2.4 T, BV0
BT2.4 T, BV?0.02 T
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ICWC in TEXTOR(C-coated wall)
? see G.Sergienko, P2-45, 27/05/2008
Removal rate
Measured removal rate for m3 vs BT
Calculated absorbed power vs BT

• ?10?cH (BT?0.2 T) Effective conditioning due
  to high antenna coupling and homogeneity possible
  in both, low and high the BT-fields
• ??cH (BT?2.3 T) Mode conversion in
  (HeH2)-plasmas is the best scenario for ICWC
  (coupling homogeneity fast particles)
• Applied BV-field (BV ltlt BT) ? increased ICWC
  yield

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ICWC in ASDEX Upgrade (W-coated wall)
Measured removal rate for m40 vs BT
Fast particles energy/power vs BT

• Benefit from mode conversion in (HeH2)-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)

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ICWC Extrapolation to ITERscenario for operation
4
3
2
1
row 1 row 2 ?/3, f40 MHz row 3 row 4 ?/6,
f48 MHz
0.32 m
TOMCAT modeling (rpl?2.4 m, R06.2 m, BT3.6 T,
ne03x1017 m-3, Te05 eV) - Mode conversion in
(HeH2)-plasmas at two frequencies
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ICWC Extrapolation to ITERpower for operation
Modeling with 0-D plasma/transport code

• 0-D Plasma/Transport code
• ne?(1-4)?1017 m-3, Te1.5 eV, ?ioniz1-2,
  p(2-8)?10-2 Pa ?
• PRF-pl (ITER) 0.2-1.5 MW ? (?coupl?0.40) ? PRF-G
  (ITER)?0.5-3.8 MW
• Extrapolation from TEXTOR data (assuming similar
  power density and ?coupl?0.40)
• PRF-pl (TEXTOR) ? 12-30 kW ? P RF-pl (ITER) ?
  1.0-2.5 MW ? P RF-G (ITER)? 2.5-6.0 MW

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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 (BVltltBT) 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.