H-mode pedestal and threshold studies over an expanded operating space on Alcator C-Mod

This paper reports on studies of the edge transport barrier and transition threshold of the high confinement (H) mode of operation on the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)], over a wide range of toroidal field (2.6–7.86T) and plasma current (0.4–1.7MA). The H-mode power threshold and edge temperature at the transition increase with field. Barrier widths, pressure limits, and confinement are nearly independent of field at constant current, but the operational space at high B shifts toward higher temperature and lower density and collisionality. Experiments with reversed field and current show that scrape-off-layer flows in the high-field side depend primarily on configuration. In configurations with the B×∇B drift away from the active X-point, these flows lead to more countercurrent core rotation, which apparently contributes to higher H-mode thresholds. In the unfavorable case, edge temperature thresholds are higher, and slow evolution of profiles indicates a red...

[1]  F. Wagner,et al.  Development of an Edge Transport Barrier at the H-Mode Transition of ASDEX , 1984 .

[2]  B. Lipschultz.  Operation of Alcator C-Mod with high-Z plasma facing components and implications , 2005 .

[3]  Brian Labombard,et al.  Edge profile stiffness and insensitivity of the density pedestal to neutral fuelling in Alcator C-Mod edge transport barriers , 2007 .

[4]  Comparisons of small ELM H-Mode regimes on the Alcator C-Mod and JFT-2M tokamaks , 2006 .

[5]  Brian Labombard,et al.  Transport-driven Scrape-Off-Layer flows and the boundary conditions imposed at the magnetic separatrix in a tokamak plasma , 2004 .

[6]  J. Stober,et al.  Pedestal conditions for small ELM regimes in tokamaks , 2006 .

[7]  P. C. Stangeby,et al.  Comparison of H-mode barrier width with a model of neutral penetration length , 2004 .

[8]  Norio Suzuki,et al.  H-Mode Power Threshold Database for ITER , 1996 .

[9]  R. S. Granetz,et al.  H-Mode Pedestal and L-H Transition Studies on Alcator C-Mod , 2007 .

[10]  M. Porkolab,et al.  Transport phenomena in the edge of Alcator C-Mod plasmas , 2005 .

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

[12]  P. T. Bonoli,et al.  Radiofrequency-heated enhanced confinement modes in the Alcator C-Mod tokamak , 1997 .

[13]  Martin Greenwald,et al.  H-Mode Pedestal Characteristics and MHD Stability of the Edge Plasma in Alcator C-Mod , 2002 .

[14]  M. Greenwald,et al.  Evidence for electromagnetic fluid drift turbulence controlling the edge plasma state in the Alcator C-Mod tokamak , 2005 .

[15]  H. Zohm,et al.  Identification of plasma-edge-related operational regime boundaries and the effect of edge instability on confinement in ASDEX Upgrade , 1997 .

[16]  Brian Labombard,et al.  Advances in measurement and modeling of the high-confinement-mode pedestal on the Alcator C-Mod tokamak , 2006 .

[17]  Local threshold conditions and fast transition dynamics of the L?H transition in Alcator C-Mod , 2004 .

[18]  A. Loarte,et al.  Scaling laws for edge plasma parameters in ITER from two-dimensional edge modelling , 2003 .

[19]  J. Rice,et al.  Observations of Anomalous Momentum Transport in Alcator C-Mod Plasmas with No Momentum Input , 2004 .

[20]  J. Snipes,et al.  Local variables affecting H-mode threshold on Alcator C-Mod , 1998 .

[21]  S. J. Wukitch,et al.  Transport-driven scrape-off layer flows and the x-point dependence of the L-H power threshold in Alcator C-Mod , 2005 .

[22]  Joseph A. Snipes,et al.  Latest results on the H-mode threshold using the international H-mode threshold database , 2000 .

[23]  P. T. Bonoli,et al.  First results from Alcator‐C‐MOD* , 1994 .

[24]  R. J. Groebner,et al.  Critical edge parameters for H-mode transition in DIII-D , 1997 .

[25]  J. Snipes,et al.  The dynamics and structure of edge-localized-modes in Alcator C-Mod , 2007 .

[26]  A. Hubbard,et al.  Physics and scaling of the H-mode pedestal , 2000 .

[27]  E. Doyle,et al.  Slow L-H transitions in DIII-D plasmas. , 2002, Physical review letters.

[28]  The dependence of core rotation on magnetic configuration and the relation to the H-mode power threshold in Alcator C-Mod plasmas with no momentum input , 2005 .

[29]  Y. Wang,et al.  H mode confinement in Alcator C-Mod , 1997 .

[30]  J. Stober,et al.  H-mode power threshold and transition in ASDEX Upgrade , 1998 .

[31]  Brian Labombard,et al.  Observations and empirical scalings of the high-confinement mode pedestal on Alcator C-Mod , 2002 .

[32]  J. Snipes,et al.  First ohmic H modes in ALCATOR C-MOD , 1994 .

[33]  A. Hubbard,et al.  Variation of edge gradients with heat flux across L-H and H-L transitions in Alcator C-Mod , 2002 .

[34]  Jerry Hughes,et al.  High-resolution edge Thomson scattering measurements on the Alcator C-Mod tokamak , 2000 .

[35]  P. T. Bonoli,et al.  Toroidal rotation and momentum transport in Alcator C-Mod plasmas with no momentum input , 2004 .