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

ELM Control Using External ELM Control Using External Perturbation Fields on JETPerturbation Fields on JET

Y Liang, JET-EFDA contributorsJoint Pedestal/SOL ITPA MeetingGarching (7-10 May), Germany

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

ContributorsY 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, Germany2 Association EURATOM-CEA, 13108 St Paul-lez-Durance, France3 Laboratory for Plasmaphysics, ERM/KMS, TEC, Association EURATOM-Belgian State, Brussels, Belgium4 EURATOM-UKAEA Fusion Association, Culham Science Centre, OX14 3DB, Abingdon, OXON, UK5 Oak Ridge National Laboratory, Oak Ridge, TN 37831-6169, Tennessee, USA6 Associazione EURATOM-ENEA sulla Fusione, Consorzio RFX Padova, Italy7 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, Belgium9 Asociacion EURATOM-CIEMAT, Avenida Complutense 22, E-28040 Madrid, Spain10 Max-Planck-Institut für Plasmaphysik, EURATOM-Assoziation, D-85748 Garching, Germany11 Association EURATOM-Risø National Laboratory, Optics and Plasma Research Department, OPL-128, P.O.Box 49, DK-4000 Roskilde, Denmark12 Association EURATOM-VR, SE 10378 Stockholm, Sweden13 Association EURATOM-Hellenic Republic, NCSR "Demokritos"153 10, Agia Paraskevi Attica, Greece

* [email protected]


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


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.2 576 (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 • collisionlessH-mode plasmas

T Evans, PRL 92 235003 (2004)

Nature physics Vol. 2 419 (2006)

Mechanism: Edge ergodisation?


Error Field Correction Coils on JET

EFCCs

• 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

n = 1n = 2


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 EFCCsn=2

Z (

m)

(r

ad)

R (m) R (m)

BR (T) for IEFCC =1kAtn=1

R (m)

EFCC n=1 EFCC n=2

= 0

n=123

n=123


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.

fELM: 30↑~120 Hz

ID : ↓ one order of magnitude

Teped: 500-700↓ ~100 – 200 eV W/W : 7%↓~2%

Reduced fast ion lossesThe electron density in the centre and at the edge decreased (pump-out effect)Increased central electron and ion temperaturesELM 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 JETNo or only a moderate (up to 20%) degradation of energy confinement time(TRANSP)

Y Liang et al, to be published on PRL (2007)

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


Reduction in ELM energy loss W/W

without EFCCs with EFCCs#67958

16.96 17 17.04Time (s)

#67959

17.78 17.79 17.80Time (s)

D D

WDia WDia


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 effectEdge profiles (see talk by M. Beurskens, 08-May)


Influence of n=1 field on confinement


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?


ELM mitigation with n=2 field

12 14 16 18 20Time (s)

PNBI

IEFCC

ne,l

D

#70472 1.85 T / 1.6 MA0

10

0

1

0

0

1

EFCCs in n=2 configuration

Less effect on core MHD

Better edge ergodisation (more resonant surfaces)


Plasma braking by the external fields

#69564 1.5 MA / 1.8 T; PNBI=9.2MW #70472 1.6 MA / 1.85 T; PNBI=8.8MW

EFCC n=2EFCC n=1

Similar plasma braking effect observed with n=1 and n=2 external fields

IEFCC=24 kAt IEFCC=24 kAt


q95 scan

IEFCC

Da

#67959

17 18Time (s)

#67954

17 18Time (s)

#68211

17 18Time (s)

#68212

17 18Time (s)

q95=4.8 / Ip=1.4MA

EFCC n=1; Bt = 1.84 T; Plasma configuration: C_SFE_LTq95=4.0 / Ip=1.6MA q95=3.5 / Ip=1.8MA q95=3.0 / Ip=2.0MA

q95 = 3.1/ 1.6 MA

12 14 16 18 20Time (s)

PNBI

IEFCC

ne,l

D

#70477

fELM = 15 / 38 Hz

12 14 16 18 20Time (s)

PNBI

IEFCC

ne,l

D

#70476

fELM = 10 / 35 Hz

q95 = 4.0 / 1.25 MA

12 14 16 18 20Time (s)

PNBI

IEFCC

ne,l

D

#70475

fELM = 10 / 18 Hz

q95 = 4.5 / 1.1 MA

EFCC n=2; Bt = 1.6 T; Plasma configuration: V_SFE_LT


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

wider operational window.


ELM mitigation in different plasmaconfigurations

HT3

Modified HT3

C_SFE_LTVIR_LC_LT

HT-3; “ITER-like”; EFCCs in n=1; Ip = 1.8 MA; Bt = 2.05 T; PNBI = 10.4 MW

14 16 18 20 22Time (s)

D (a.u.)

ne,l (1020 m-2)

IEFCC (kA)

u, l

PNBI (MW)0

10

2

1.5

0

0.5

-2

0.45

0.35

JET#69515


ELM mitigation with an n = 1 field in high plasmas

4 8765Time (s)

PNBI

D

ne,l

N

IEFCC0

0

01

-1

10

1

2

0

6

#68973 1.2 MA / 1.8 T

therm0.3

N ~ 2.5; Same beam power request to keep beta constantThermal energy confinement constantELM mitigation threshold <16 kAtNo locked mode excited by EFCC n=1 field

Real-time beta control EFCC Switched on


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 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


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”


EFCCs on ITER

Documents

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