ELM Control Using ELM Control Using External Perturbation External Perturbation Fields on JET Fields on JET Y Liang, JET-EFDA contributors Joint Pedestal/SOL ITPA Meeting Garching (7-10 May), Germany
Dec 29, 2015
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
7-10 May, 2007Y 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, 2007Y 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.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?
7-10 May, 2007Y 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
• 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
7-10 May, 2007Y 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 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
7-10 May, 2007Y 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.
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
7-10 May, 2007Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany
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
7-10 May, 2007Y 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 effectEdge profiles (see talk by M. Beurskens, 08-May)
7-10 May, 2007Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany
Influence of n=1 field on confinement
7-10 May, 2007Y 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, 2007Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany
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)
7-10 May, 2007Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany
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
7-10 May, 2007Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany
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
7-10 May, 2007Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany
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.
7-10 May, 2007Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany
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
7-10 May, 2007Y Liang - Joint Pedestal/SOL ITPA Meeting, Garching, Germany
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
7-10 May, 2007Y 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 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
7-10 May, 2007Y 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”