1. A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 1 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 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

2. A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 2 Outline Motivation ICRF Plasma / Antenna Coupling Characterization ICWC in TEXTOR and ASDEX Upgrade ICWC Extrapolation to ITER Conclusions

3. A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 3 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.

4. A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 4 Plasma Production with Standard ICRF Antennas TEXTOR ICRF antennas f =25-38 MHz, B T =0.25-2.5 T, p=(1-10 )  10 -2 Pa AUG ICRF antennas f =30.0; 36.5 MHz, B T =1.0-2.4 T, p=(1-8 )  10 -2 Pa RF Field/Waves excitation RF Power e-collisional absorption Neutral Gas e-collisional ionization

5. A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 5 ICWC Optimization ICRF Plasma Production Removal Mechanisms Antenna Coupling Plasma Homogeneity / Extension Fast Ions Generation 1. High Ion Cyclotron Harmonics,  =n  ci, n>>1 2. Mode Conversion,  =  ci B T +B V, B V <<B T Fundamental Ion Cyclotron Resonance  =  ci

6. A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 6 TEXTOR: ICRF Plasma Characterization  ICRF plasma can be produced at any B T -field   =10  cH+ (B T  0.2 T): High coupling (  0.8), density (>2  10 17 m -3 ) and homogeneity   =  cH+ (B T  2.3 T): improved coupling (  0.5) and homogeneity n e, T e and P pl vs B T

7. A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 7 AUG: ICRF Plasma Characterization Mode conversion scenario in (He+H 2 )-plasmas:  Higher antenna coupling (up to 3 times)  Better homogeneity and extension in radial direction  Better performance at two frequencies (He+H 2 )-plasma vs He-plasma B T +B V vs B T Vertical magnetic field improves plasma homogeneity in poloidal dirction and extends it towards divertor He, f =30 MHzHe+H 2, f =30 MHz He+H 2, f 1 =30 MHz+ f 2 =36.5 MHz BTBT BTBT BVBV B T =2.4 T, B V =0 B T =2.4 T, B V  0.02 T

8. A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 8 ICWC in TEXTOR (C-coated wall)   =10  cH+ (B T  0.2 T): Effective conditioning due to high antenna coupling and homogeneity possible in both, low and high the B T -fields   =  cH+ (B T  2.3 T): Mode conversion in (He+H 2 )-plasmas is the best scenario for ICWC (coupling + homogeneity + fast particles)  Applied B V -field (B V << B T )  increased ICWC yield Removal rate: Measured removal rate for m=3 vs B T Calculated absorbed power vs B T  see G.Sergienko, P2-45, 27/05/2008

9. A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 9 ICWC in ASDEX Upgrade (W-coated wall)  Benefit from mode conversion in (He+H 2 )-mixture with ICR (  =  cH+ ) location closer to the antenna  ICWC output correlates with fast particles energy and power absorbed by protons  B V -field improves the ICWC effect  Major concern – ICWC homogeneity (efficient cleaning from ~25% of the AUG surface) Measured removal rate for m=40 vs B T Fast particles energy/power vs B T

10. A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 10 ICWC Extrapolation to ITER: scenario for operation 0.32 m row 1 & row 2:  /3, f=40 MHz row 3 & row 4:  /6, f=48 MHz 1 2 3 4 TOMCAT modeling (r pl  2.4 m, R 0 =6.2 m, B T =3.6 T, n e0 =3x1017 m-3, T e0 =5 eV): - Mode conversion in (He+H 2 )-plasmas at two frequencies

11. A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 11 Modeling with 0-D plasma/transport code 1.0-D Plasma/Transport code: n e  (1-4)  10 17 m -3, T e ~1.5 eV,  ioniz =1-2%, p=(2-8)  10 -2 Pa  P RF-pl (ITER) = 0.2-1.5 MW  (  coupl  0.40)  P RF-G (ITER)  0.5-3.8 MW 2.Extrapolation from TEXTOR data (assuming similar power density and  coupl  0.40): P RF-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

12. A.Lyssoivan – 18PSI, Toledo, Spain 27/05/2008 12 Conclusions Inter-machine (TEXTOR, ASDEX Upgrade) ICWC studies:  Wall conditioning in the mode conversion scenario in the presence of toroidal and vertical magnetic fields (B V <<B T ) 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.