Advances in H-mode physics for long-pulse operation on EAST

Since the 2012 International Atomic Energy Agency Fusion Energy Conference (IAEA-FEC), significant advances in both physics and technology has been made on the Experimental Advanced Superconducting Tomakak (EAST) toward a long-pulse stable high-confinement (H-mode) plasma regime. The experimental capabilities of EAST have been technically upgraded with the power enhancement (source power up to 26 MW) of the continuous-wave heating and current drive system, replacement of the upper graphite divertor with an ITER-like W monoblock divertor, and installation of a new internal cryopump in the upper divertor and a set of 16 in-vessel resonant magnetic perturbation (RMP) coils. This new upgrade enables EAST to be a unique operating device capable of investigating ITER-relevant long-pulse high-performance operations with dominant electron heating and low torque input within the next 5 years. Remarkable physics progress in controlling transient and steady-state divertor heat fluxes has been achieved on EAST, e.g. (i) edge-localized mode (ELM) mitigation/suppression with a number of attractive methods including lower hybrid wave (LHW), supersonic molecular beam injection (SMBI), RMPs, and real-time Li aerosol injection; and (ii) active control of steady-state power distribution by the synergy of LHW and SMBI. In the 2014 experimental campaign, a long-pulse high-performance H-mode plasma with H98 ~ 1.2 has been obtained with a duration over 28 s (~200 times the energy confinement time). In addition, several new experimental advances have been achieved in the last EAST campaign, including: (i) high-performance H-mode with βN ~ 2 and stored plasma energy ~220 kJ; (ii) H-mode plasma sustained by neutral beam injection (NBI) alone or modulated NBI with lower hybrid current drive (LHCD), for the first time in EAST; (iii) high current drive efficiency and nearly full noninductive plasmas maintained by the new 4.6 GHz LHCD system; (iv) demonstration of a quasi-snowflake divertor configuration; and (v) observation of a new edge-coherent mode and its effects on edge transport in H-mode plasmas.

[1]  J. Contributors,et al.  Scaling of the tokamak near the scrape-off layer H-mode power width and implications for ITER , 2013 .

[2]  Yingying Li,et al.  Scaling of divertor power footprint width in RF-heated type-III ELMy H-mode on the EAST superconducting tokamak , 2014 .

[3]  Weiye Xu,et al.  Preliminary investigation of the effects of lower hybrid power on asymmetric behaviors in the scrape-off layer in experimental advanced superconducting tokamak , 2014 .

[4]  S. J. Wukitch,et al.  Absorption of lower hybrid waves in the scrape off layer of a diverted tokamak , 2010 .

[5]  R. Bell,et al.  Continuous improvement of H-mode discharge performance with progressively increasing lithium coatings in the National Spherical Torus Experiment. , 2011, Physical review letters.

[6]  P. Diamond,et al.  ELM mitigation by supersonic molecular beam injection: KSTAR and HL-2A experiments and theory , 2014 .

[7]  G. Calabrò,et al.  Study of lower hybrid current drive efficiency over a wide range of FTU plasma parameters , 2005 .

[8]  B. Wan,et al.  Study on H-mode access at low density with lower hybrid current drive and lithium-wall coatings on the EAST superconducting tokamak , 2011 .

[9]  T. Xia,et al.  Six-field two-fluid simulations of peeling–ballooning modes using BOUT++ , 2013 .

[10]  B. Wan,et al.  Characterizations of power loads on divertor targets for type-I, compound and small ELMs in the EAST superconducting tokamak , 2013 .

[11]  Gang Xu,et al.  A long-pulse high-confinement plasma regime in the Experimental Advanced Superconducting Tokamak , 2013, Nature Physics.

[12]  G Schettini,et al.  Current drive at plasma densities required for thermonuclear reactors. , 2010, Nature communications.

[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]  Alfredo Pironti,et al.  EAST alternative magnetic configurations: modelling and first experiments , 2015 .

[15]  Z. Xiaodong,et al.  Development of a Fast Valve for Disruption Mitigation and its Preliminary Application to EAST and HT-7 , 2013 .

[16]  D. Ryutov.  Geometrical properties of a “snowflake” divertor , 2007 .

[17]  Ling Zhang,et al.  Experimental investigations of LHW–plasma coupling and current drive related to achieving H-mode plasmas in EAST , 2013 .

[18]  J. Garcia,et al.  MHD stability of the pedestal in ITER scenarios , 2013 .

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

[20]  T. Osborne,et al.  High-frequency coherent edge fluctuations in a high-pedestal-pressure quiescent H-mode plasma. , 2011, Physical review letters.

[21]  E. Joffrin,et al.  Chapter 6: Steady state operation , 2007 .

[22]  M. Sugihara,et al.  Disruption scenarios, their mitigation and operation window in ITER , 2007 .

[23]  J. Chen,et al.  Overview of R&D on Plasma-Facing Materials and Components in China , 2012 .

[24]  P. Diamond,et al.  Study of the L–I–H transition with a new dual gas puff imaging system in the EAST superconducting tokamak , 2013 .

[25]  M. Sugihara,et al.  Characteristics of type I ELM energy and particle losses in existing devices and their extrapolation to ITER , 2003 .

[26]  G. R. Hanson,et al.  Effects of LH power on SOL density profiles and LH coupling on Alcator C-Mod , 2013 .

[27]  L. Lao,et al.  Kinetic equilibrium reconstruction on EAST tokamak , 2013 .

[28]  A. M. Garofalo,et al.  Recent advances in long-pulse high-confinement plasma operations in Experimental Advanced Superconducting Tokamaka) , 2014 .

[29]  B N Wan,et al.  Magnetic topology changes induced by lower hybrid waves and their profound effect on edge-localized modes in the EAST tokamak. , 2013, Physical review letters.

[30]  J. S. deGrassie,et al.  Effect of island overlap on edge localized mode suppression by resonant magnetic perturbations in DIII-D , 2008 .

[31]  P. T. Bonoli,et al.  Simulation model for lower hybrid current drive , 1986 .

[32]  J. Garcia,et al.  Lower hybrid current drive for the steady-state scenario , 2010 .

[33]  Orso Meneghini,et al.  Lower hybrid current drive at high density in Alcator C-Mod , 2011 .

[34]  Houyang Guo,et al.  Progress of long pulse and H-mode experiments in EAST , 2013 .

[35]  Y. Kamada,et al.  Pedestal stability comparison and ITER pedestal prediction , 2009 .

[36]  V. Rozhansky,et al.  Measurements of impurity and heat dynamics during noble gas jet-initiated fast plasma shutdown for disruption mitigation in DIII-D , 2004 .

[37]  B N Wan,et al.  New edge coherent mode providing continuous transport in long-pulse H-mode plasmas. , 2014, Physical review letters.

[38]  J. Decker,et al.  Numerical Simulations of the Radio-Frequency–driven Toroidal Current in Tokamaks , 2014 .

[39]  R. Sartori,et al.  Edge localized modes: recent experimental findings and related issues , 2007 .

[40]  P. Parks,et al.  First observations of ELM triggering by injected lithium granules in EAST , 2013 .

[41]  Brian Labombard,et al.  Analysis of a multi-machine database on divertor heat fluxesa) , 2011 .

[42]  A. Diallo,et al.  Observation of edge instability limiting the pedestal growth in tokamak plasmas. , 2014, Physical review letters.

[43]  Jiansheng Hu,et al.  Comparison between gas puffing and supersonic molecular beam injection in plasma density feedback experiments in EAST , 2013 .

[44]  L. L. Lao,et al.  Compatibility of internal transport barrier with steady-state operation in the high bootstrap fraction regime on DIII-D , 2015, Nuclear Fusion.

[45]  R. Maingi,et al.  New steady-state quiescent high-confinement plasma in an experimental advanced superconducting tokamak. , 2015, Physical review letters.

[46]  L. Colas,et al.  Edge plasma density convection during ion cyclotron resonance heating on Tore Supra , 2002 .

[47]  Nbi Team,et al.  First Achievement of Plasma Heating for EAST Neutral Beam Injector , 2015 .

[48]  A. D. Turnbull,et al.  Stationary, high bootstrap fraction plasmas in DIII-D without inductive current control , 2005 .

[49]  M. Becoulet,et al.  Resonant magnetic perturbation experiments on MAST using external and internal coils for ELM control , 2010 .

[50]  R. H. Bulmer,et al.  Sustained Spheromak Physics Experiment (SSPX): design and physics results , 2012 .