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ELM Control Using External Perturbation Fields on JET

ELM Control Using External Perturbation Fields on JET. Y Liang, JET-EFDA contributors Joint Pedestal/SOL ITPA Meeting Garching (7-10 May), Germany. Contributors. Y Liang 1* , H R Koslowski 1 , P R Thomas 2 , E Nardon 2 , S Jachmich 3 ,

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ELM Control Using External Perturbation Fields on JET

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  1. ELM Control Using External Perturbation Fields on JET Y Liang, JET-EFDA contributors Joint Pedestal/SOL ITPA Meeting Garching (7-10 May), Germany

  2. Contributors Y Liang1*, H R Koslowski1,P R Thomas2, E Nardon2, S Jachmich3, B Alper4, Ph Andrew4, Y Andrew4, G Arnoux2, Y Baranov4, M Becoulet2, M Beurskens4, T Biewer5, M Bigi6, I Coffey7, K Crombe8, E De La Luna9, P de Vries4, Th Eich10, W Fundamenski4, S Gerasimov4, C Giroud4, M Gryaznevich4, D Harting1, N Hawkes4, S Hotchin4, D Howell4, M Jakubowski1, V Kiptily4, L Moreira4, S K Nielsen11,V Parail4, S D Pinches4, E Rachlew12, O Schmitz1, M Tsalas13, M Zerbini6, O Zimmermann1, and JET-EFDA contributors 1 Association EURATOM-Forschungszentrum Jülich, TEC, D-52425 Jülich, Germany 2 Association EURATOM-CEA, 13108 St Paul-lez-Durance, France 3 Laboratory for Plasmaphysics, ERM/KMS, TEC, Association EURATOM-Belgian State, Brussels, Belgium 4 EURATOM-UKAEA Fusion Association, Culham Science Centre, OX14 3DB, Abingdon, OXON, UK 5 Oak Ridge National Laboratory, Oak Ridge, TN 37831-6169, Tennessee, USA 6 Associazione EURATOM-ENEA sulla Fusione, Consorzio RFX Padova, Italy 7 Department of Pure and Applied Physics, Queens University, Belfast, BT7 1NN, UK 8 Association EURATOM-Belgian State, Department of Applied Physics Ghent University, B-9000 Ghent, Belgium 9 Asociacion EURATOM-CIEMAT, Avenida Complutense 22, E-28040 Madrid, Spain 10 Max-Planck-Institut für Plasmaphysik, EURATOM-Assoziation, D-85748 Garching, Germany 11 Association EURATOM-Risø National Laboratory, Optics and Plasma Research Department, OPL-128, P.O.Box 49, DK-4000 Roskilde, Denmark 12 Association EURATOM-VR, SE 10378 Stockholm, Sweden 13 Association EURATOM-Hellenic Republic, NCSR "Demokritos"153 10, Agia Paraskevi Attica, Greece * y.liang@fz-juelich.de Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

  3. ITER baseline scenario • ELMy H-mode • Extrapolated (type-I) ELM losses are not tolerable • ITER needs ELM mitigation • Smaller ELMs are good for JET ILW, too Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

  4. Previous experiments on active ELM control with magnetic perturbation fields in tokamaks Triggering of small ELMs in ELM-free H-mode plasmas JFT-2M (n>4) M Mori et al, 14th IAEA Vol.2 576 (1992). Increasing the frequency of Type-III ELMs S J Fielding et al, ECA 25A 1825 (2001) COMPASS-D (n=1; m=4-5) • Complete suppression of type-I ELMs in • collisional and • collisionless • H-mode plasmas DIII-D (n=3) T Evans, PRL 92 235003 (2004) Nature physics Vol. 2 419 (2006) Mechanism:Edge ergodisation? Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

  5. Error Field Correction Coils on JET n = 1 n = 2 • Four square shaped coils (~ 6m in dimension) positioned outside of JET vessel • ICoil ≤ 3 kA x 16 turns • Main purpose of these coils is to compensate n=1 intrinsic error fields • Depending on the relative phasing of the currents in individual coils, either n=1 or n=2 fields can be generated. • EFCCs have been successfully used to mitigate ELMs with external perturbation fields on JET 5.3 – 7 m 70o EFCCs Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

  6. Magnetic Perturbations Induced by EFCCs n=2 n=1 BR (T) for IEFCC =1kAt f (rad) Z (m) R (m) R (m) R (m) F = 0 • n=1 • Weak edge ergodisation • Plasma braking • Seeding of locked modes • n=2 • Good edge ergodisation • Less influence on core plasma EFCC n=2 EFCC n=1 n=1 2 3 n=1 2 3 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

  7. Mitigation of Type-I ELMs by application of an n=1 external perturbation field on JET Ip = 1.6 MA; Bt = 1.84 T; q95 ~ 4.0; d ~ 0.3 • Amplitude andfrequency of the type-I ELMs are actively controlled by adjusting the amplitude of the n = 1 externalperturbation field induced by the EFCCs on JET. • fELM:30↑~120 Hz • ID :↓ one order of magnitude • DTeped: 500-700↓~100 – 200 eV • DW/W : 7%↓~2% • Reduced fast ion losses • The electron density in the centre and at the edge decreased (pump-out effect) • Increased central electron and ion temperatures • ELM mitigation does not depend on the phase of n = 1 external field, however, there are good phases and bad phases with respect to the position and boundary control system on JET • No or only a moderate (up to 20%) degradation of energy confinement time(TRANSP) Y Liang et al, to be published on PRL (2007) Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

  8. Reduction in ELM energy loss DW/W #67959 17.79 17.78 17.80 Time (s) without EFCCs with EFCCs #67958 Da Da WDia WDia 17 16.96 17.04 Time (s) Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

  9. Influence of n=1 field on profiles • Electron and ion temperaturesare increasedduring ELM mitigation phase • Electron density decreases everywhere (centre and edge) due to pump-out effect • Edge profiles (see talk by M. Beurskens, 08-May) Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

  10. Influence of n=1 field on confinement Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

  11. Active control of Type-I ELM by n = 1 field • ELM frequency, edge density, and temperature drop during ELM follow perturbation field amplitude (above threshold) • Hysteresis or non-stationary nature of the experiment? Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

  12. ELM mitigation with n=2 field 10 PNBI #70472 1.85 T / 1.6 MA 0 1 IEFCC 0 1 ne,l 0 Da 0 12 14 16 18 20 Time (s) • EFCCs in n=2 configuration • Less effect on core MHD • Better edge ergodisation (more resonant surfaces) Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

  13. Plasma braking by the external fields EFCC n=2 EFCC n=1 #70472 1.6 MA / 1.85 T; PNBI=8.8MW #69564 1.5 MA / 1.8 T; PNBI=9.2MW IEFCC=24 kAt IEFCC=24 kAt • Similar plasma braking effect observed with n=1 and n=2 external fields Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

  14. q95 scan PNBI PNBI PNBI IEFCC IEFCC IEFCC ne,l ne,l ne,l #67959 #68212 #68211 #67954 Da Da Da IEFCC 12 12 12 14 14 14 16 16 16 18 18 18 20 20 20 Time (s) Time (s) Time (s) Da #70476 #70475 #70477 17 18 17 18 17 18 17 18 Time (s) Time (s) Time (s) Time (s) fELM = 10 / 18 Hz fELM = 15 / 38 Hz fELM = 10 / 35 Hz EFCC n=1; Bt = 1.84 T; Plasma configuration: C_SFE_LT q95=3.0 / Ip=2.0MA q95=4.0 / Ip=1.6MA q95=3.5 / Ip=1.8MA q95=4.8 / Ip=1.4MA EFCC n=2; Bt = 1.6 T; Plasma configuration: V_SFE_LT q95 = 3.1/ 1.6 MA q95 = 4.0 / 1.25 MA q95 = 4.5 / 1.1 MA Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

  15. Operational window for ELM mitigation EFCC n=1; Bt = 1.84 T; C_SFE_LT • Locked mode threshold in H-mode plasma is much higher than that in L-mode plasma ( ~ few hundreds A). • The minimum perturbation field amplitude above which the ELMs were mitigated increased but always remained below the n=1 locked mode threshold. • EFCC n=2: likely to have a wideroperational window. Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

  16. ELM mitigation in different plasmaconfigurations HT3 10 Modified HT3 PNBI (MW) JET#69515 0 0.45 0.35 du, dl 2 IEFCC (kA) 0 C_SFE_LT -2 VIR_LC_LT ne,l (1020 m-2) 1.5 0.5 Da(a.u.) 14 16 18 20 22 Time (s) HT-3; “ITER-like”; EFCCs in n=1; Ip = 1.8 MA; Bt = 2.05 T; PNBI = 10.4 MW Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

  17. ELM mitigation with an n = 1 field in high b plasmas #68973 1.2 MA / 1.8 T PNBI 10 EFCC Switched on 0 IEFCC 1 0 -1 bN 2 1 ttherm 0.3 0 Da ne,l 6 0 4 5 6 7 8 Time (s) Real-time beta control • bN ~ 2.5; Same beam power request to keep beta constant • Thermal energy confinement constant • ELM mitigation threshold <16 kAt • No locked mode excited by EFCC n=1 field Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

  18. Summary • Experimental results from JET show that type-I ELMs can be mitigated by the application of an low n (1 or 2) external perturbation field • ELM frequency increases by factor up to ~4 • The electron density in the centre and at the edge decreased (pump-out effect) • The electron and ion temperatures increased at plasma core while smaller changes at plasma edge • DW/W reduces below 2% • ELMs were successfully mitigated at low and high triangularity • There is a wide range in q95 (4.8 – 3.0) in which ELM mitigation with the low n (1 or 2) external perturbation field has been observed • Transport analyses shows an acceptable reduction in thermal energy confinement (0 to 20%, depends on scenario) • The effect on ELMs (lower bound) and the excitation of a locked mode (upper bound) form an operational window for EFCC usage for ELM mitigation • ELM mitigation does not depend on the phase of the external fields, however, there are good phases and bad phases with respect to the position and boundary control system on JET (The temperature of the outer limiter dropped during when the EFCCs were applied with a good phase) • Similar plasma braking effect observed with n=1 and n=2 external fields Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

  19. Tokamak operating scenarios must avoid large ELMs, even at the cost of a partial loss of confinement. P H Rebut 2006 PPCF 48 B1-B13 “Hannes Alfvén Price Lecture 2006” Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

  20. EFCCs on ITER Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany

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