Discovery of stationary operation of quiescent H-mode plasmas with net-zero neutral beam injection torque and high energy confinement on DIII-D

Recent experiments in DIII-D [J. L. Luxon et al., in Plasma Physics and Controlled Nuclear Fusion Research 1996 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] have led to the discovery of a means of modifying edge turbulence to achieve stationary, high confinement operation without Edge Localized Mode (ELM) instabilities and with no net external torque input. Eliminating the ELM-induced heat bursts and controlling plasma stability at low rotation represent two of the great challenges for fusion energy. By exploiting edge turbulence in a novel manner, we achieved excellent tokamak performance, well above the H98y2 international tokamak energy confinement scaling (H98y2 = 1.25), thus meeting an additional confinement challenge that is usually difficult at low torque. The new regime is triggered in double null plasmas by ramping the injected torque to zero and then maintaining it there. This lowers E × B rotation shear in the plasma edge, allowing low-k, broadband, electromagnetic turbul...

[1]  L. Lao,et al.  Quiescent double barrier high-confinement mode plasmas in the DIII-D tokamak , 2001 .

[2]  T. Fujita,et al.  Energy loss for grassy ELMs and effects of plasma rotation on the ELM characteristics in JT-60U , 2005 .

[3]  P. Snyder,et al.  Progress in the peeling-ballooning model of edge localized modes: Numerical studies of nonlinear dynamicsa) , 2005 .

[4]  O. Meneghini,et al.  The quiescent H-mode regime for high performance edge localized mode-stable operation in future burning plasmasa) , 2014 .

[5]  R. Neu,et al.  ELM-free stationary H-mode plasmas in ASDEX Upgrade , 2003 .

[6]  T. Osborne,et al.  Rotational shear effects on edge harmonic oscillations in DIII-D quiescent H-mode discharges , 2015 .

[7]  T. Osborne,et al.  Characterization of peeling–ballooning stability limits on the pedestal , 2004 .

[8]  T. H. Osborne,et al.  Enhanced H-mode pedestals with lithium injection in DIII-D , 2015 .

[9]  Maxim Umansky,et al.  Stability and dynamics of the edge pedestal in the low collisionality regime: physics mechanisms for steady-state ELM-free operation , 2007 .

[10]  T. Osborne,et al.  Quiescent H-mode operation using torque from non-axisymmetric, non-resonant magnetic fields , 2013 .

[11]  T. Osborne,et al.  Edge stability of stationary ELM-suppressed regimes on DIII-D , 2008 .

[12]  H. R. Wilson,et al.  A first-principles predictive model of the pedestal height and width: development, testing and ITER optimization with the EPED model , 2011 .

[13]  T. Osborne,et al.  Reactor-relevant quiescent H-mode operation using torque from non-axisymmetric, non-resonant magnetic fieldsa) , 2012 .

[14]  L. L. Lao,et al.  ELMs and constraints on the H-mode pedestal: peeling–ballooning stability calculation and comparison with experiment , 2004 .

[15]  D. J. Campbell,et al.  Chapter 1: Overview and summary , 1999 .

[16]  T. Osborne,et al.  Edge pedestal control in quiescent H-mode discharges in DIII-D using co-plus counter-neutral beam injection , 2008 .

[17]  P. B. Snyder,et al.  The EPED pedestal model and edge localized mode-suppressed regimes: Studies of quiescent H-mode and development of a model for edge localized mode suppression via resonant magnetic perturbations , 2012 .

[18]  K. H. Burrell,et al.  Flow shear induced fluctuation suppression in finite aspect ratio shaped tokamak plasma , 1995 .

[19]  G. Staebler,et al.  Impurity confinement and transport in high confinement regimes without edge localized modes on DIII-Da) , 2015 .

[20]  E. Doyle,et al.  Pedestal profiles during QH-mode operation on DIII-D , 2004 .

[21]  J. Snipes,et al.  Pedestal profiles and fluctuations in C-Mod enhanced D-alpha H-modes , 2000 .

[22]  David J. Schlossberg,et al.  Turbulence velocimetry of density fluctuation imaging data , 2004 .

[23]  L. L. Lao,et al.  Advances in understanding quiescent H-mode plasmas in DIII-D , 2005 .

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

[25]  Impact of toroidal rotation on ELM behaviour in the H-mode on JT-60U , 2004 .

[26]  T. Osborne,et al.  Quiescent H-mode plasmas with strong edge rotation in the cocurrent direction. , 2009, Physical Review Letters.

[27]  Naoto Tsujii,et al.  I-mode: an H-mode energy confinement regime with L-mode particle transport in Alcator C-Mod , 2010 .

[28]  Peter Lang,et al.  Studies of the ‘Quiescent H-mode’ regime in ASDEX Upgrade and JET , 2005 .

[29]  T. Osborne,et al.  Access to a new plasma edge state with high density and pressures using the quiescent H mode. , 2014, Physical review letters.

[30]  K. Burrell,et al.  Advances towards QH-mode viability for ELM-stable operation in ITER , 2011 .

[31]  A. Diallo,et al.  Response of impurity particle confinement time to external actuators in QH-mode plasmas on DIII-D , 2014 .

[32]  L. Lao,et al.  Edge stability of the ELM-free quiescent H-mode on DIII-D , 2005 .