Active control of type-I edge localized modes on JET. Invited Paper

The operational domain for active control of type-I edge localized modes (ELMs) with an n = 1 external magnetic perturbation field induced by the ex-vessel error field correction coils on JET has been developed towards more ITER-relevant regimes with high plasma triangularity, up to 0.45, high normalized beta, up to 3.0, plasma current up to 2.0 MA and q95 varied between 3.0 and 4.8. The results of ELM mitigation in high triangularity plasmas show that the frequency of type-I ELMs increased by a factor of 4 during the application of the n = 1 fields, while the energy loss per ELM, ΔW/W, decreased from 6% to below the noise level of the diamagnetic measurement (<2%). No reduction of confinement quality (H98Y) during the ELM mitigation phase has been observed. The minimum n = 1 perturbation field amplitude above which the ELMs were mitigated increased with a lower q95 but always remained below the n = 1 locked mode threshold. The first results of ELM mitigation with n = 2 magnetic perturbations on JET demonstrate that the frequency of ELMs increased from 10 to 35 Hz and a wide operational window of q95 from 4.5 to 3.1 has been found.

[1]  D. J. Campbell,et al.  Chapter 1: Overview and summary , 1999 .

[2]  Vallet,et al.  Stabilization of tokamak Ohmic discharges at the density limit by means of the ergodic divertor. , 1991, Physical review letters.

[3]  H. Koslowski,et al.  Dependence of the threshold for perturbation field generated m/n = 2/1 tearing modes on the plasma fluid rotation , 2006 .

[4]  M E Fenstermacher,et al.  Suppression of large edge-localized modes in high-confinement DIII-D plasmas with a stochastic magnetic boundary. , 2004, Physical review letters.

[5]  R. L. Haye,et al.  Error field mode studies on JET, COMPASS-D and DIII-D, and implications for ITER , 1999 .

[6]  O. Sauter,et al.  Error field locked modes thresholds in rotating plasmas, anomalous braking and spin-up , 2002 .

[7]  L. Horton,et al.  ELM energy and particle losses and their extrapolation to burning plasma experiments , 2003 .

[8]  J. S. deGrassie,et al.  RMP ELM suppression in DIII-D plasmas with ITER similar shapes and collisionalities , 2008 .

[9]  J. W. Connor,et al.  Edge-localized modes - physics and theory , 1998 .

[10]  M. Mori.  Active control of H-mode , 1996 .

[11]  J. B. Lister,et al.  Magnetic triggering of ELMs in TCV , 2003 .

[12]  W. Kerner,et al.  Plasma confinement in JET H?mode plasmas with H, D, DT and T isotopes , 1999 .

[13]  N Hawkes,et al.  Active control of type-I edge-localized modes with n=1 perturbation fields in the JET tokamak. , 2007, Physical review letters.

[14]  L. Rossi,et al.  The error field correction coils on the JET machine , 2001 .

[15]  M. G. Bell,et al.  Simulations of alpha parameters in a TFTR DT supershot with high fusion power , 1995 .

[16]  L. Horton,et al.  ELM pace making and mitigation by pellet injection in ASDEX Upgrade , 2004 .

[17]  Keith H. Burrell,et al.  Edge stability and transport control with resonant magnetic perturbations in collisionless tokamak plasmas , 2006 .

[18]  G. Matthews,et al.  Effect of plasma configuration on carbon migration measured in the inner divertor of JET using quartz microbalance , 2005 .

[19]  F. Wagner,et al.  Regime of Improved Confinement and High Beta in Neutral-Beam-Heated Divertor Discharges of the ASDEX Tokamak , 1982 .