1. TORE SUPRA 1 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 Recent results on ICWC D. Douai 1, A. Lyssoivan 2, V. Philipps 3, S. Brezinsek 3, V. Rohde 4, T. Wauters 1,2 T.Blackman 5, V. Bobkov 4, S. Brémond 1, E. de la Cal 6, T.Coyne 5, M. Garcia-Munoz 4, E. Gauthier 1, M.Graham 5, S.Jachmich 2, E.Joffrin 1, A. Kreter 3, P.U. Lamalle 7, E.Lerche 2, G.Lombard 1, M. Maslov 5, M.-L. Mayoral 5, P. Mollard 1, I. Monakhov 5, A.Miller 5, J.-M. Noterdaeme 4,8, J. Ongena 2, M.K. Paul 3, B. Pégourié 1, R. Pitts 7, V. Plyusnin 9, F.C. Schüller 7, G. Sergienko 3, M. Shimada 7, W. Suttrop 4, C.Sozzi 10, M.Tsalas 11, E. Tsitrone 1, D.Van Eester 2, the TORE SUPRA Team, the TEXTOR Team, the ASDEX Upgrade Team and JET EFDA Contributors* 1 CEA, IRFM, Association Euratom-CEA, 13108 St Paul lez Durance, France. 2 LPP-ERM/KMS, Association Euratom-Belgian State, 1000 Brussels, Belgium, TEC partner. 3 IEF-Plasmaphysik FZ Jülich, Euratom Association, 52425 Jülich, Germany, TEC partner 4 Max-Planck Institut für Plasmaphysik, Euratom Association, 85748 Garching, Germany. 5 CCFE, Culham Science Centre, OX14 3DB, Abingdon, UK. 6 Laboratorio Nacional de Fusión, Association Euratom-CIEMAT, 28040 Madrid, Spain. 7 ITER International Organization, F-13067 St Paul lez Durance, France. 8 Gent University, EESA Department, B-9000 Gent, Belgium. 9 Centro de FNIST, Association Euratom-IST, 1049-001 Lisboa, Portugal. 10 IFP­CNR, EURATOM­ENEA­CNR Fusion Association, Milano Italy. 11 NCSR ‘Demokritos’, Athens, Greece *See the Appendix of F. Romanelli et al., Proc. 22nd Int. FEC Geneva, IAEA (2008) Plan: - Context - Selection of obtained experimental (and numerical) results on TORE SUPRA, TEXTOR, AUG and JET - Conclusion & future plans

2. TORE SUPRA 2 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 Context Conventional Glow Discharge Conditioning inefficient in the presence of permanent B tor Need for alternative wall conditioning techniques compatible with B tor - Plasma initiation (Impurities, fuel removal) - Control of discharge content (isotopic ratio) - Tritium removal in ITER ICWC : the most promising one : low energy + fast neutrals Experiments conducted in TS, Textor, AUG and JET in the frame of a collaborative work Context Goals: Characterization of Ion Cyclotron Wall Conditioning (ICWC) discharges Optimization and assessment of efficiency

3. TORE SUPRA 3 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 Main parameters of ICWC discharges  B T = 3,8 T  (1-x)He:xH 2, x = 0  0,6  p Torus = 5.10 -2  10 -1 Pa  Sinusoidal B R +B V  Freq. = 48 MHz (ITER 40-55 MHz)  25 kW < P ICRF < 150 kW  0 and  -phasing operation  CW and pulsed operation Q2 RF antenna 0,72 m Exhaust + MS  Superconducting tokamak  R = 2.4 m, a = 0,72 m  ~ 70 m 2 stainless steel alloy 316L  ~ 14 m 2 CFC N11  T wall = 120°C 1H ICR

4. TORE SUPRA 4 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 n H /[n H +n D ] in ohmic shots (by means of NPA) after 15+3’ ICWC Reference ohmic shot before ICWC  Isotopic ratio measured during reference ohmic shots on PTL  high isotopic exchange after ~15 min. ICWC in He-H 2  Recovery to ohmic plasma after 3 min. He-ICWC discharge (walls saturated with H) Isotopic exchange  What is the ratio between implanted and desorbed particles ?

5. TORE SUPRA 5 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 Isotopic ratio change from 1 to 20 % after 60 sec. ICWC After that, one NSB (wall saturation by H atoms) Before ICWC After ~60 sec. He:H 2 ICWC n H /[n H +n D ] in ohmic shots (by means of NPA) AUG Strong Hydrogen isotopic exchange also in all-W AUG

6. TORE SUPRA 6 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 Weak D 2 partial pressure ! P HD ~ 3 10 -3 Pa Q HD ~ 2.3 10 18 mol./s RR HD ~ 2.7 10 16 mol./m 2 /s H implanted = 2.3 10 21 D pumped = 2.2 10 20 H implanted /D pumped ~ 10 Particle balance : outpumped particles vs. injected particles TS#43463 P RF ~50 kW, He-30% H 2 - 60 sec. long continuous operation of Q2 antenna  Long term outgassing with t -0,6±0,1, indicating diffusion process of desorbed species Isotopic exchange

7. TORE SUPRA 7 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 P~0,1 Pa, P RF ~ 50 kW H 2 depletion is decreasing from 90 to 45% within 10 discharges (i.e. ~10 min. He-H 2 ICWC)  Wall saturation by H atoms Wall saturation

8. TORE SUPRA 8 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 within ~ 850 sec. of CW ICWC in He-H 2 : Total D desorbed : 3,4.10 21 D  2 “monolayers” Total H implanted : 3,2.10 22 H  H implanted /D pumped = 9.4 Some signs of equilibrium between ICWC and wall after 15 min. D removal and H implantation

9. TORE SUPRA 9 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 1. Right after glow discharge almost all injected H is lost to the walls 2. Amount of out pumped D decreases from shot to shot  change IR wall 3. Amount of H lost to the wall remains constant at the end of the day  At end of day wall flux becomes predominantly H Study evolution of (D 2 -loaded) wall during isotope exchange experiments 26 Nearly identical He/H 2 ICWC discharges Similar result on TORE SUPRA, JET Particle balance for every ICWC discharge  Also observed in Textor

10. TORE SUPRA 10 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 Recovery from disruption (TS)  2 disruptions on outboard poloidal limiter at I p =1,2 MA (dI p /dt ~360 MA/s)  Each time, recovery after only 1 pulsed He-ICWC discharge (ON/OFF = 2s/8s  10 pulses) Low ohmic current pulsed discharges (“Taylor-like”) He- ICWC DC-glows He  Q HD ~ 1-2 10 18 mol./s  Similar with other conditioning techniques ICWC disruptions Ohmic shots Non sustained breakdown

11. TORE SUPRA 11 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 Pulsed ICWC discharges  Pulsed He-ICWC discharge, duty cycle = 2 sec. ON / 8 sec. OFF  Increase due to summation of aftershot pressure level  Decrease due to wall desaturation (approach to p(H 2 )= 0)  Duty cycle can be decreased  2:20 or more New results on pulsed discharges under analysis TS#43532 P RF ~60 kW, ~0,1 Pa

12. TORE SUPRA 12 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 Simulation of ITER full field ICWC on JET  Development of He / D 2 -ICWC operation in conditions similar to ITER full field operation i.e. B T =5.3 T and 40-55 MHz frequency band for the ITER ICRF system  same (f/B T )-ratio at JET gives B T =3.3 T and 25 MHz for on-axis  =  CD +  A2-D@ 25.21 MHz, A2-C@26.06 MHz. JET antennas used for ICWC Location of ICR layers in JET Torus at f=25 MHz

13. TORE SUPRA 13 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 Main concern: Arcing in the VTL due to the high neutral gas pressure. –VTL pressure trips reduced to 10 -5 mbar (~5.10 -5 mbar in Torus) –MTL voltages restricted to 20kV maximum –New VSWR cards installed –Maximum of 10 trips per pulse / 100 trips for the whole experiment –risk reduced by applying the RF before the gas injection 9 sec. RF ON KL1-8-w (Wide visible camera) # 78582 D 2 : 4 He ~ 0.85:0.15 General waveform for RF and gas injection Antenna safe operation JET

14. TORE SUPRA 14 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 reflectometry (KG10)  n e measured up to R=3.0 m t=45 sec. pulse #78579, ~ 60kW interferometry (KG1)  n e higher at LFS than at HFS pulse #79323, D 2 -ICWC LID1 (HFS) LID4 (LFS) ECE  Te ~ a fews tens of eV Discharge characterisation JET not in agreement

15. TORE SUPRA 15 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 He retention during shot He puff pulse #78588, He-ICWC He retention in JET Ex: pure He-ICWC pulse (#78588), coupled RF power = 80 kW  He implanted = 8.10 20  D outgassed = 2.10 21 Antenna protection limiters in Bulk Be He retention also observed in all W AUG pure He ohmic Partial pressures from optical Penning gauges No wall preloading Particle balance & He retention in He containing ICWC discharges Over the whole session: 25% of D retained during the session released with 2 pure He –ICWC shots (no wall preloading) But 4% He/D measured in 1st ohmic (#78590) x 2,5

16. TORE SUPRA 16 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 He retention observed in AUG W-materials during ICWC Also observed in DC glows Important He retention also seen in AUG He puff He retention during shot AUG#28458 P RF-coupled ~150-200 kW, He:H 2 =50:50 D release AUG Note: unfortunately the gas-injection of H2 and He was kept on until t=16 s

17. TORE SUPRA 17 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 3.Assessment of efficiency for wall conditioning / isotopic exchange - wall pre-loading with H 2 -GDC hydrogen prior to the session - NO reference OH shot - Isotopic Exchange using D 2 -ICWC - 8 identical RF discharges in D 2 : p= 2.10 -5 mbar, P RF,coupled = 250 kW, B V =30 mT - Analysis of gas after the cryo-pump regeneration by chromatography D/(H+D) increases by 30% (divertor) or 50% (midplane spectroscopy) Higher D/H ratio measured by spectroscopy (KS3B horizontal channel) than with divertor Penning gauges

18. TORE SUPRA 18 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 within ~ 70 sec. of D 2 –ICWC + post-discharge 1,8.10 22 H outgassed   7 “monolayers” 5,2.10 22 D implanted H outgassed / D implanted = 0,3 From mass spectrometry (including post-discharge) Particle balance Pressure set to 2.10 -5 mbar in the RF discharge Some difficulties to couple RF power to discharges Analysis by chromatography of gas after regeneration of cryo-pumping (incl. pumping time between discharges) Note: H 2 is weakly pumped by cryo-pumps at 4.8 K below 10 -5 mbar Within 70 sec. D 2 -ICWC: 1,6.10 22 H outgassed 4,8.10 22 D retained Q H =1,2.10 18 m -2.s -1 Q D, retention =3,4.10 18 m -2.s -1 to be compared with short term retention accessible by plasma operation : 2.10 23 D atoms

19. TORE SUPRA 19 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 1.Integrated fast CX D flux ( ∫ 4  S JET.  D dt, with energies > 1keV) is function of RF coupled power 2.Influence of CX D flux on H pumped not obvious 3.D retention is higher than CX D flux Influence of fast CX D neutrals vs. low D+? Fast CX neutrals (from NPA) JET D charge exchange neutrals measured up to 50 keV Fast H-atoms (  =1/2  CH + @r=0  absorption mechanism?)

20. TORE SUPRA 20 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010  Arcing traces on Q2 antenna straps  Shallow damages due to “micro-arcs” that propagates at the surface of the strap  Deposition or heating pattern visible on FS, no arcing trace  plasma between FS and straps  Unipolar arcs  For P > 120 kW, antenna protection triggered on too high reflected power/forwarded power ratio within 10µsec., discharge stopped after 20 trig. Q2 antenna He ICWC RF operation (TS)

21. TORE SUPRA 21 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 Goal:qualify the routine operation and the reliability of Ion Cyclotron Wall Conditioning (ICWC) in view of ITER  disruption recovery  manage H, D, T wall content  control of the impurities influx Existing ICRF transmitters To Tore Supra standard IC antenna (2 straps) New ICWC dedicated antenna - upper port? (single or double strap low power -200 kW- simple design with double stub matching unit) RF switch Some specs:  Same frequencies (42-73 MHz),  Work at any B T  RF Power coupled to ICWC discharge : a few tens up to ~200 kW  Wide Working pressure range (a few 10 -3 Pa up to a few Pa) Dedicated ICWC antenna on TORE SUPRA

22. TORE SUPRA 22 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 Modelling of ICWC (PhD T. Wauters) 0D ‘kinetic’ description of H 2 /He ICWC discharges Data to be combined with data from RF models (e.g. TOMCAT, D. Van Eester) and plasma wall interaction codes Wall reservoir modeling to simulate isotopic ratio change over

23. TORE SUPRA 23 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010  ICWC discharges investigated in TS, JET, AUG and TEXTOR  Recovery from disruptions demonstrated in TORE SUPRA, using pulsed He-ICWC  optimisation of pulsed ICWC discharges under study  He / D 2 -ICWC scenarios in divertor tokamaks in conditions similar to ITER half and full field operation  AUG: B T =2,0 T and f=30MHz for on-axis  =  CH +  JET: B T =3.3 T and 25 MHz for on-axis  =  CD +  Strong isotopic ratio exchange in H 2 (or D 2 ) ICWC discharges  However always 2 to 10 more retention than outgassing  pulsed ICWC  In JET, ICWC discharges could reach the central column. The equivalent of 10~20 % of the short term retained H could be exchanged with D within 70 sec. D 2 -ICWC (p = 2.10 -5 mbar, P RF,coupled = 250 kW, B V =30 mT), with 1 H outgassed for 3 D retained  A large He retention during He containing ICWC discharges in JET and AUG  AUG: known from He-GDC and lab experiments  JET : reason ?  presence of Be as bulk material for antenna protection limiters  Flux of CX neutrals too low to explain outgassing and retention quantitatively  Arcing traces on antenna straps  Need for antenna dedicated to ICWC in TS. Conclusion

24. TORE SUPRA 24 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010 TS: superconducting tokamak - Analysis of Pulsed discharges data on going - High P/N discharges - Assess efficiency against different type of disruptions - Role of CX neutrals (use of NPA) vs. low energy species (RFA) - Project of dedicated antenna JET : assessment of efficiency on JET with ILW (Be first wall + W divertor) - Repeat reference session on isotopic exchange with ILW - assess He as working gas for ICWC with ILWNo specific wall “preloading” (or with ohmic shots) Future plans