TFM

6 Nov 2006H R Koslowski, Workshop on Active Control of MHD Stability, Princeton

ELM mitigation by external coils on JETELM mitigation by external coils on JET

W.FundamenskiW.Fundamenski

On behalf ofOn behalf of

R.Koslowski, Y.Liang, P.Thomas and EFDA-JET contributorsR.Koslowski, Y.Liang, P.Thomas and EFDA-JET contributors

TFM

6 Nov 2006H R Koslowski, Workshop on Active Control of MHD Stability, Princeton

n=1n=2

Aim: Control type-I ELMs

Tool: Error Field Correction Coils (EFCC), proposed by Y Liang

n=1

• Weak edgeergodisation

• Plasma braking

• Seeding oflocked modes

n=2

• Good edge ergodisation

• Small influence on core plasma

First results on active ELM control on JET

ICoil ≤ 3 kA x 16 turns

TFM

6 Nov 2006H R Koslowski, Workshop on Active Control of MHD Stability, Princeton

EFCC ELM mitigation experiment

#67954; Ip = 1.6 MA; Bt = 1.84 T; q95 ~ 4.0; ~ 0.3

t=18.0s

t=17.0s

IEFCC

WDia

D

q95

P

H98

N

14 1816 Time (s)

Wdia<10%

fELMs= 28 120 Hz

OH + 16.8 MW NBI

C_SFE_LT

TFM

6 Nov 2006H R Koslowski, Workshop on Active Control of MHD Stability, Princeton

Influence of RMP (n=1) on ne and Te

IEFCC

nel central

nel edge

Te central

Te edge

Teped = 500-700 eV 100-200eV

needge; ne

edge;

>20%

17 17.5 18 18.5Time (s)

Increased by ~17%

decreased by ~15%

TFM

6 Nov 2006H R Koslowski, Workshop on Active Control of MHD Stability, Princeton

Limiter heat loading

Without EFCC

With EFCC

16 17 18 19 20 21

Temperature

outer limiter

Temperature

outer limiter

IEFCC

Time (s)

NBI

EFCC off

EFCC on

(n=1, 90o)

TFM

6 Nov 2006H R Koslowski, Workshop on Active Control of MHD Stability, Princeton

Ergodisation?

Equilibrium: B0=1.84T; q95=3.95; =0.5;

For 1 kA*16 turns

[Calculated By: M. Bécoulet and E. Nardon]

TFM

6 Nov 2006H R Koslowski, Workshop on Active Control of MHD Stability, Princeton

q95 Scan

Neutron rate

IEFCC

D

#68212#68211#67954#67959

17 18Time (s)

17 18Time (s)

17 18Time (s)

17 18Time (s)

Ip=1.4MA

q95=4.8

Bt=1.84 T; Plasma configuration: C_SFE_LT(68207-68212)

Ip=1.6MA

q95=4.0

Ip=1.8MA

q95=3.5

Ip=2.0MA

q95=3.0

TFM

6 Nov 2006H R Koslowski, Workshop on Active Control of MHD Stability, Princeton

Summary (I)

First experimental results from JET show that type-I ELMs can be mitigated by the application of an n = 1 external perturbation field

Static n = 1 perturbation induced by the EFCCs• ELM frequency increased from ~30 Hz to ~120 Hz

• D intensity dropped by a factor of ~10

• The drop in edge temperature during the ELM was reduced from 500 – 700 eV to 100 – 200 eV

• The electron density in the centre and at the edge was reduced up to ~15%

• The central electron temperature increased by ~15%, while the change of the edge temperature is less than a few percent

TFM

6 Nov 2006H R Koslowski, Workshop on Active Control of MHD Stability, Princeton

Summary (II)

Only weak degradation (< 10%) of global plasma performance (Wdia, N)

is observed during the ELM mitigation phase

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 on JET

The temperature of the outer limiter dropped during the EFCC phase

Breaking of the central rotation has been observed when the EFCCs were applied

The sawtooth frequency during the EFCC phase increases

There is a wide range in q95 (4.8 – 3.0) in which ELM mitigation with the

n = 1 external perturbation field has been observed

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