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Recent results on ICWC

Recent results on ICWC

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Recent results on ICWC

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  1. Recent results on ICWC D. Douai1, A. Lyssoivan2, V. Philipps3, S. Brezinsek3, V. Rohde4, T. Wauters1,2 T.Blackman5, V. Bobkov4, S. Brémond1, E. de la Cal6, T.Coyne5, M. Garcia-Munoz4, E. Gauthier1, M.Graham5, S.Jachmich2, E.Joffrin1, A. Kreter3, P.U. Lamalle7, E.Lerche2, G.Lombard1, M. Maslov5, M.-L. Mayoral5, P. Mollard1, I. Monakhov5, A.Miller5 , J.-M. Noterdaeme4,8, J. Ongena2, M.K. Paul3, B. Pégourié1, R. Pitts7, V. Plyusnin9, F.C. Schüller7, G. Sergienko3, M. Shimada7, W. Suttrop4, C.Sozzi10, M.Tsalas11, E. Tsitrone1, D.Van Eester2, the TORE SUPRA Team, the TEXTOR Team, the ASDEX Upgrade Team and JET EFDA Contributors* 1CEA, IRFM, Association Euratom-CEA, 13108 St Paul lez Durance, France. 2LPP-ERM/KMS, Association Euratom-Belgian State, 1000 Brussels, Belgium, TEC partner. 3IEF-Plasmaphysik FZ Jülich, Euratom Association, 52425 Jülich, Germany, TEC partner 4Max-Planck Institut für Plasmaphysik, Euratom Association, 85748 Garching, Germany. 5CCFE, Culham Science Centre, OX14 3DB, Abingdon, UK. 6Laboratorio Nacional de Fusión, Association Euratom-CIEMAT, 28040 Madrid, Spain. 7ITER International Organization, F-13067 St Paul lez Durance, France. 8Gent University, EESA Department, B-9000 Gent, Belgium. 9Centro de FNIST, Association Euratom-IST, 1049-001 Lisboa, Portugal. 10IFP­CNR, EURATOM­ENEA­CNR Fusion Association, Milano Italy. 11NCSR ‘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 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  2. Context Context Conventional Glow Discharge Conditioning inefficient in the presence of permanent Btor Need for alternative wall conditioning techniques compatible with Btor • 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 • Goals: • Characterization of Ion Cyclotron Wall Conditioning (ICWC) discharges • Optimization and assessment of efficiency D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  3. 1H ICR 0,72 m Q2 RF antenna Exhaust + MS Main parameters of ICWC discharges • Superconducting tokamak • R = 2.4 m, a = 0,72 m • ~ 70 m2 stainless steel alloy 316L • ~ 14 m2 CFC N11 • Twall = 120°C • Freq. = 48 MHz (ITER 40-55 MHz) • 25 kW < PICRF < 150 kW • 0 and p-phasing operation • CW and pulsed operation • BT = 3,8 T • (1-x)He:xH2, x = 00,6 • pTorus = 5.10-2 10-1Pa • Sinusoidal BR+BV D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  4. nH/[nH+nD] in ohmic shots (by means of NPA) after 15+3’ ICWC Reference ohmic shot before ICWC Isotopic exchange • Isotopic ratio measured during reference ohmic shots on PTL • high isotopic exchange after ~15 min. ICWC in He-H2 • Recovery to ohmic plasma after 3 min. He-ICWC discharge (walls saturated with H) • What is the ratio between implanted and desorbed particles ? D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  5. Strong Hydrogen isotopicexchange also in all-W AUG AUG nH/[nH+nD] in ohmic shots (by means of NPA) After ~60 sec. He:H2 ICWC Before ICWC Isotopic ratio change from 1 to 20 % after 60 sec. ICWC After that, one NSB (wall saturation by H atoms) D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  6. Isotopic exchange Particle balance : outpumped particles vs. injected particles TS#43463 PRF~50 kW, He-30% H2 -60 sec. long continuous operation of Q2 antenna Weak D2 partial pressure ! PHD ~ 3 10-3 Pa QHD ~ 2.3 1018 mol./s RRHD ~ 2.7 1016 mol./m2/s Himplanted = 2.3 1021 Dpumped = 2.2 1020 Himplanted/Dpumped ~ 10 • Long term outgassing with t-0,6±0,1, indicating diffusion process of desorbed species D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  7. Wall saturation P~0,1 Pa, PRF ~ 50 kW H2 depletion is decreasing from 90 to 45% within 10 discharges (i.e. ~10 min. He-H2 ICWC)  Wall saturation by H atoms D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  8. D removal and H implantation within ~ 850 sec. of CW ICWC in He-H2 : Total D desorbed : 3,4.1021 D  2 “monolayers” Total H implanted : 3,2.1022 H  Himplanted/Dpumped = 9.4 Some signs of equilibrium between ICWC and wall after 15 min. D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  9.  Also observed in Textor Study evolution of (D2-loaded) wall during isotope exchange experiments 26 Nearly identical He/H2 ICWC discharges Particle balance for every ICWC discharge 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 Similar result on TORE SUPRA, JET D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  10. disruptions Ohmic shots Non sustained breakdown He- ICWC Low ohmic current pulsed discharges (“Taylor-like”) ICWC DC-glows He Recovery from disruption (TS) • 2 disruptions on outboard poloidal limiter at Ip=1,2 MA (dIp/dt ~360 MA/s) • Each time, recovery after only 1 pulsed He-ICWC discharge (ON/OFF = 2s/8s  10 pulses) • QHD ~ 1-2 1018 mol./s • Similar with other conditioning techniques D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  11. 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(H2)= 0) • Duty cycle can be decreased  2:20 or more New results on pulsed discharges under analysis TS#43532 PRF~60 kW, ~0,1 Pa D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  12. Simulation of ITER full field ICWC on JET • Development of He / D2-ICWC operation in conditions similar to ITER full field operation i.e. BT=5.3 T and 40-55 MHz frequency band for the ITER ICRF system • same (f/BT)-ratio at JET gives BT=3.3 T and 25 MHz for on-axis =CD+  A2-D@ 25.21 MHz, A2-C@26.06 MHz. Location of ICR layers in JET Torus at f=25 MHz JET antennas used for ICWC D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  13. Antenna safe operation 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 KL1-8-w (Wide visible camera) # 78582 D2: 4He ~ 0.85:0.15 JET General waveform for RF and gas injection 9 sec. RF ON D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  14. not in agreement LID1 (HFS) LID4 (LFS) Discharge characterisation reflectometry (KG10)  ne measured up to R=3.0 m ECE  Te ~ a fews tens of eV pulse #78579, <PRF>~ 60kW t=45 sec. interferometry (KG1)  ne higher at LFS than at HFS JET pulse #79323, D2-ICWC D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  15. He retention during shot pure He He puff ohmic pulse #78588, He-ICWC Particle balance & He retention in He containing ICWC discharges Partial pressures from optical Penning gauges He retention in JET Ex: pure He-ICWC pulse (#78588), coupled RF power = 80 kW • Heimplanted = 8.1020 • Doutgassed= 2.1021 Antenna protection limiters in Bulk Be He retention also observed in all W AUG x 2,5 • 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) No wall preloading D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

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

  17. Assessment of efficiency for wall conditioning / isotopic exchange • wall pre-loading with H2-GDC hydrogen prior to the session • NO reference OH shot • Isotopic Exchange using D2-ICWC • 8 identical RF discharges in D2 : p= 2.10-5 mbar, PRF,coupled = 250 kW, BV=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 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  18. Particle balance From mass spectrometry (including post-discharge) Pressure set to 2.10-5 mbar in the RF discharge Some difficulties to couple RF power to discharges within ~ 70 sec. of D2 –ICWC + post-discharge 1,8.1022 H outgassed   7 “monolayers” 5,2.1022 D implanted Houtgassed / Dimplanted= 0,3 Analysis by chromatography of gas after regeneration of cryo-pumping (incl. pumping time between discharges) Note: H2 is weakly pumped by cryo-pumps at 4.8 K below 10-5 mbar to be compared with short term retention accessible by plasma operation : 2.1023 D atoms Within 70 sec. D2-ICWC: 1,6.1022 H outgassed 4,8.1022 D retained QH=1,2.1018 m-2.s-1 QD, retention =3,4.1018 m-2.s-1 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

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

  20. RF operation (TS) • 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 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  21. Dedicated ICWC antenna on TORE SUPRA • 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 New ICWC dedicated antenna - upper port? (single or double strap low power -200 kW- simple design with double stub matching unit) RF switch To Tore Supra standard IC antenna (2 straps) Existing ICRF transmitters • Some specs: • Same frequencies (42-73 MHz), • Work at any BT • 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) D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  22. Modelling of ICWC (PhD T. Wauters) 0D ‘kinetic’ description of H2/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 D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  23. Conclusion • 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 / D2-ICWC scenarios in divertor tokamaks in conditions similar to ITER half and full field operation • AUG: BT=2,0 T and f=30MHz for on-axis =CH+ • JET: BT=3.3 T and 25 MHz for on-axis =CD+ • Strong isotopic ratio exchange in H2 (or D2) 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. D2-ICWC (p = 2.10-5 mbar, PRF,coupled = 250 kW, BV=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. D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

  24. Future plans • 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) D. Douai Recent results on Ion Cyclotron Wall conditioning 15 April 2010

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