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

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany Contributors Y Liang 1*, H R Koslowski 1, P R Thomas 2, E Nardon 2, S Jachmich 3, B Alper 4, Ph Andrew 4, Y Andrew 4, G Arnoux 2, Y Baranov 4, M Becoulet 2, M Beurskens 4, T Biewer 5, M Bigi 6, I Coffey 7, K Crombe 8, E De La Luna 9, P de Vries 4, Th Eich 10, W Fundamenski 4, S Gerasimov 4, C Giroud 4, M Gryaznevich 4, D Harting 1, N Hawkes 4, S Hotchin 4, D Howell 4, M Jakubowski 1, V Kiptily 4, L Moreira 4, S K Nielsen 11, V Parail 4, S D Pinches 4, E Rachlew 12, O Schmitz 1, M Tsalas 13, M Zerbini 6, O Zimmermann 1, and JET-EFDA contributors 1 Association EURATOM-Forschungszentrum Jülich, TEC, D J ü lich, Germany 2 Association EURATOM-CEA, 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 , 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 Madrid, Spain 10 Max-Planck-Institut für Plasmaphysik, EURATOM-Assoziation, D 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 Stockholm, Sweden 13 Association EURATOM-Hellenic Republic, NCSR "Demokritos"153 10, Agia Paraskevi Attica, Greece *

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany 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

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany Previous experiments on active ELM control with magnetic perturbation fields in tokamaks Triggering of small ELMs in ELM-free H-mode plasmas M Mori et al, 14th IAEA Vol (1992). JFT-2M (n>4) COMPASS-D (n=1; m=4-5) S J Fielding et al, ECA 25A 1825 (2001) Increasing the frequency of Type-III ELMs DIII-D (n=3) Complete suppression of type-I ELMs in collisional and collisionless H-mode plasmas T Evans, PRL (2004) Nature physics Vol (2006) Mechanism: Edge ergodisation?

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany Error Field Correction Coils on JET EFCCs Four square shaped coils (~ 6m in dimension) positioned outside of JET vessel I Coil ≤ 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 70 o n = 1n = 2

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany n=1 Weak edge ergodisation Plasma braking Seeding of locked modes n=2 Good edge ergodisation Less influence on core plasma Magnetic Perturbations Induced by EFCCs n=2 Z (m)  (rad) R (m) B R (T) for I EFCC =1kAt n=1 R (m) EFCC n=1 EFCC n=2  = 0 n=123n=123 n=123n=123

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany Mitigation of Type-I ELMs by application of an n=1 external perturbation field on JET Amplitude and frequency of the type-I ELMs are actively controlled by adjusting the amplitude of the n = 1 external perturbation field induced by the EFCCs on JET. f ELM : 30 ↑ ~120 Hz I D  : ↓ one order of magnitude  T e ped : ↓ ~100 – 200 eV  W/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) I p = 1.6 MA; B t = 1.84 T; q 95 ~ 4.0;  ~ 0.3

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany Reduction in ELM energy loss  W/W without EFCCswith EFCCs # Time (s) # Time (s) DD DD W Dia

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany Influence of n=1 field on profiles  Electron and ion temperatures are increased during ELM mitigation phase  Electron density decreases everywhere (centre and edge) due to pump-out effect  Edge profiles (see talk by M. Beurskens, 08-May)

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany Influence of n=1 field on confinement

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany 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?

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany ELM mitigation with n=2 field Time (s) P NBI I EFCC n e,l DD # T / 1.6 MA  EFCCs in n =2 configuration  Less effect on core MHD  Better edge ergodisation (more resonant surfaces)

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany Plasma braking by the external fields # MA / 1.8 T; P NBI =9.2MW # MA / 1.85 T; P NBI =8.8MW EFCC n=2 EFCC n=1  Similar plasma braking effect observed with n=1 and n=2 external fields I EFCC =24 kAt

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany q 95 scan I EFCC DaDa # Time (s) # Time (s) # Time (s) # Time (s) q 95 =4.8 / I p =1.4MA EFCC n=1; B t = 1.84 T; Plasma configuration: C_SFE_LT q 95 =4.0 / I p =1.6MAq 95 =3.5 / I p =1.8MA q 95 =3.0 / I p =2.0MA q 95 = 3.1 / 1.6 MA Time (s) P NBI I EFCC n e,l DD #70477 f ELM = 15 / 38 Hz Time (s) P NBI I EFCC n e,l DD #70476 f ELM = 10 / 35 Hz q 95 = 4.0 / 1.25 MA Time (s) P NBI I EFCC n e,l DD #70475 f ELM = 10 / 18 Hz q 95 = 4.5 / 1.1 MA EFCC n=2; B t = 1.6 T; Plasma configuration: V_SFE_LT

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany Operational window for ELM mitigation EFCC n=1; B t = 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 wider operational window.

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany ELM mitigation in different plasma configurations HT3 Modified HT3 C_SFE_LT VIR_LC_LT HT-3; “ITER-like”; EFCCs in n=1; I p = 1.8 MA; B t = 2.05 T; P NBI = 10.4 MW Time (s) D  (a.u.) n e,l (10 20 m -2 ) I EFCC (kA)  u,  l P NBI (MW) JET#69515

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany ELM mitigation with an n = 1 field in high  plasmas Time (s) P NBI DD n e,l NN I EFCC # MA / 1.8 T  therm 0.3  N ~ 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 Real-time beta control EFCC Switched on

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany 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   W/W reduces below 2%  ELMs were successfully mitigated at low and high triangularity  There is a wide range in q 95 (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

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany 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”

7-10 May, 2007 Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany EFCCs on ITER