EX/4-2: Active Control of Type-I Edge Localized Modes with n = 1 and n = 2 fields on JET

Transcription

1 EX/4-2: Active Control of Type-I Edge Localized Modes with n = 1 and n = 2 fields on JET Y Liang (FZ Jülich), JET-EFDA contributors IAEA Fusion Energy Conference, Geneva, Switzerland 13-18/10/2008

2 Page 2/17 Contributors Y. Liang1, H. R. Koslowski1, P. R. Thomas2, E. Nardon3, S. Jachmich4, A. Alfier5, G. Arnoux6, Y. Baranov3, M. Bécoulet6, M. Beurskens3, R. Coelho7, Th. Eich8, E. De La Luna9, W. Fundamenski3, S. Gerasimov3, C. Giroud3, M. P. Gryaznevich3, D Harting1, A. Huber1, A. Kreter1, L. Moreira3, V. Parail3, S. D. Pinches3, S. Saarelma3, O. Schmitz1, and JET-EFDA contributors* JET-EFDA, Culham Science Centre, OX14 3DB, Abingdon, UK 1Forschungszentrum Jülich GmbH, Association EURATOM-FZ Jülich, Institut für Energieforschung - Plasmaphysik, Trilateral Euregio Cluster, D Jülich, Germany; 2Fusion for Energy Joint Undertaking, Josep Pl. 2, Torres Diagonal Litoral B3, 08019, Barcelona, Spain 3EURATOM-UKAEA Fusion Association, Culham Science Centre, OX14 3DB, Abingdon, OXON, UK; 4Association EURATOM-Belgian State, Koninklijke Militaire School - Ecole Royale Militaire, B-1000 Brussels Belgium; 5Associazione EURATOM-ENEA sulla Fusione, Consorzio RFX Padova, Italy; 6Association EURATOM-CEA, St Paul-lez-Durance, France; 7Associação EURATOM/IST, Centro de Fusão Nuclear, Instituto Superior Técnico, Av Rovisco Pais, Lisbon, Portugal 8Max-Planck-Institut für Plasmaphysik, EURATOM-Assoziation, D Garching, Germany; 9Asociación EURATOM-CIEMAT, Avenida Complutense 22, E Madrid, Spain; contact of the main author: y.liang@fz-juelich.de * See the Appendix of F. Romanelli et al., paper OV/1-2, this conference

3 Page 3/17 DIII-D (n=3) In-vessel Coils JET (n=1, 2) External Coils Complete suppression of type-i ELMs in collisionless H-mode plasmas Mitigation (Increasing the frequency and reducing the size) of type-i ELMs in H-mode plasmas Mechanism: Edge ergodisation? Introduction T Evans, PRL, 92, (2004) Nature physics, Vol. 2, 419 (2006) Y Liang, PRL, 98, (2007) PPCF, 49, B581 (2007) Application: How to maintain the plasma density? This method should be tested for ITER-like plasmas, i.e. high Ip, high triangularity.

4 Outlines Introduction Error Field Correction Coils (EFCCs) on JET Experimental results of ELM mitigation with low n external magnetic perturbation fields ELM mitigation with n = 1 and n = 2 field Compensation of density pump-out effect with gas puffing ELM Control in a low rotation plasma with TF ripple Summary Page 4/17

5 Page 5/17 EFCC system on JET IEFCC = 1 kat; Bt= 1.84 T Depending on the relative phasing of the currents in individual coils, either n=1 or n=2 fields can be generated ICoil 2.3 ka x 16 turns (n = 1); ICoil 2.0 ka x 16 turns (n = 2) R ~ 6 m; Size ~ 6 m * 6 m Br at wall ~ 0.25 mt/kat

6 ELM control with a low n external magnetic perturbation field Page 6/17 n = 1 field felm increases by factor 4 to 5 W/W reduces from 6% to below the noise level of measurement (2%) The electron density in the centre and at the edge decreased (pump-out effect) No or moderate reduction in thermal energy confinement Y.Liang et al., PPCF 2007

7 Heat and particle fluxes onto the divertor JET #69555, Ip = 1.8 MA, Bt = 2.16 T, q95 = 4.4, δ = 0.45; PNBI = 9.5 MW, nel = 1.3 (1020m-2), IEFCC = 32 kat Outer Strike Line (Measured by embedded Langmuir probes) Reduction of ELM peak heat No much effect on the inter-elm heat flux S. Jachmich, et al., EPS 2007 Page 7/17

8 Change of edge profiles of mitigated ELMs with n = 1 fields Page 8/17 JET#69557 With n = 1 field the edge ne is reduced (density pump-out effect) by ~20% while the edge Te is increased. the edge pressure gradient pe is reduced by ~20% the edge pressure barrier is 20% wider A. Alfier et al., Nucl. Fusion, 2008

9 Stability analysis of mitigated ELMs with n = 1 fields Type I ELM phase Mitigated phase The stability of the edge plasma is studied using the ELITE code. With n = 1 perturbation field the operational point moves from intermediate-n peeling-ballooning (wide mode) boundary to low-n peeling (narrow mode) boundary S. Saarelma et al., subm. to PPCF, 2008 Page 9/17

10 Active control of type-i ELM by n = 1 field ELM frequency and temperature drop during ELM follow perturbation field amplitude (above threshold) Y.Liang et al., PRL 2007 Page 10/17

11 Operational window Wide range in q95 ( ) The minimum perturbation field amplitude for ELM mitigation increased but remained always below the n=1 locked mode threshold. Y.Liang et al., PPCF 2007 Page 11/17

12 Page 12/17 Operational domain Operational domain of ELM mitigation with n = 1 field has been developed towards ITER-relevant regimes U L Plasma current: I ~ 2.0 MA Low collisionality:

13 ELM mitigation with n = 2 field JET #70472 Bt = 1.85 T / Ip = 1.6 MA/ q95=4.0 PNBI (x10 MW) IEFCC (x16 kat) 24 kat e ne,l (x1020m-2) core Te (kev) edge edge core Dα (a.u ) Time (s) Y.Liang et al., PPCF 2007 Y. Liang Page 13/17 22nd IAEA Fusion Energy Conference, Geneva 13-18/10/2008

14 Compensation of density pump-out effect with gas puffing (I) Ip = 2 MA; Bt = 1.85 T; q95 = 3.2; PNBI = 11.2 MW; δu = 0.2; δl = 0.4 n GWL = 0.95 n GWL = 0.73 No gas fueling: ne drops after IEFCC>IcriticalEFCC ne continually drops even with a flat-top of IEFCC. (non- steady state) n GWL = 0.68 n GWL = 0.55 With gas fueling: ne can be maintained during the application of IEFCC with a optimized gas rate. Further increase ne density need (ngwl>0.73) need to be Y. Liang et al., PSI, 2008 investigated. Y. Liang Page 14/17 22nd IAEA Fusion Energy Conference, Geneva 13-18/10/2008

15 Compensation of density pump-out effect with gas puffing (II) Below the optimised fuelling rate, the mitigated ELM frequency stays at a similar value ELM-peak radiation dropped significantly for the mitigated ELMs With an optimised gas puffing, Prad at inter-elm phase increased by a factor of 2 (30% of Ptotal), while a change of the ELM-peak radiation is small. No difference in the stored energy between the discharges with and without an optimized gas fueling. Page 15/17

16 ELM Control in a low rotation plasma with TF ripple Ip = 2.0 MA; Bt = 2.2 T; q95 = 3.6; PNBI=10.8 MW Less toroidal rotation braking and density pump-out due to an application of magnetic perturbation has been observed in the plasmas with large TF ripple of 0.8%. No clear change of the locked mode threshold even in a low rotation plasma with TF ripple Page 16/17

17 Conclusion Experimental results from JET show that type-i ELMs can be active controlled by the application of an n = 1, 2 external perturbation field ELM frequency increases by factor 4 to 5; W/W reduces below 2%; Reduction in ELM peak heat fluxes and carbon erosion Pump-out effects electron density; Electron and ion temperatures increase (core and edge) Moderate reduction in thermal energy confinement H98(y,2) stays constant ELMs were successfully mitigated in low and high δ H-modes and at high beta Wide range in q95 ( ) where ELM mitigation with n = 1, 2 works Wide operational window for different target plasmas (high beta, high δ, ITER base-line scenarios) Operational window below locked mode threshold (for n=1) exists The mitigated ELM with n = 1 field have a similar power scaling as type-i ELMs Compensation of the density pump-out effect has been achieved with gas fuelling The plasma density can be maintained during the flat top of IEFCC An optimised fuelling rate to compensate the density pump-out effect without an additional drop in the plasma stored energy has been identified. Less toroidal rotation braking and density pump-out due to application of a low n magnetic perturbation has been observed in the plasmas with large TF ripple of 0.8%. Y. Liang Page 17/17 22nd IAEA Fusion Energy Conference, Geneva 13-18/10/2008