H-mode research in NSTX

H-modes are routinely obtained in the National Spherical Torus Experiment (NSTX) and have become a standard operational scenario. L–H transitions triggered by NBI heating have been obtained over a wide parameter range in Ip, Bt, and e in either lower-single-null (LSN) or double-null (DN) diverted discharges. Edge localized modes are observed in both configurations but the characteristics differ between DN and LSN, which also have different triangularities (δ). An H-mode duration of 500 ms was obtained in LSN, with a total pulse length of ~1 s. Preliminary power threshold studies indicate that the L–H threshold is between 600 kW and 1.2 MW, depending on the target parameters. Gas injector fuelling from the centre stack (i.e. the high toroidal field side) has enabled routine H-mode access, and comparisons with low-field side (LFS) fuelled H-mode discharges show that the LFS fuelling delays the L–H transition and alters the pre-transition plasma profiles. Gas puff imaging and reflectometry show that the H-mode edge is usually more quiescent than the L-mode edge. Divertor infrared camera measurements indicate up to 70% of available power flows to the divertor targets in quiescent H-mode discharges.

[1]  K. C. Lee,et al.  Results of NSTX heating experiments , 2002 .

[2]  S. Wolfe,et al.  A new look at density limits in tokamaks , 1988 .

[3]  G. F. Counsell,et al.  First physics results from the MAST Mega-Amp Spherical Tokamak , 2001 .

[4]  E. D. Fredrickson,et al.  β-Limiting MHD instabilities in improved-performance NSTX spherical torus plasmas , 2003 .

[5]  V. Soukhanovskii,et al.  Heat flux scaling experiments in NSTX , 2003 .

[6]  D. A. Gates,et al.  High β, long pulse, bootstrap sustained scenarios on the National Spherical Torus Experiment (NSTX) , 2003 .

[7]  K. C. Lee,et al.  H-mode threshold and dynamics in the National Spherical Torus Experiment , 2003 .

[8]  S. S. Medley,et al.  Confinement studies of auxiliary heated NSTX plasmas , 2004 .

[9]  J. Spitzer,et al.  Engineering design of the National Spherical Torus Experiment , 2001 .

[10]  T. Fülöp,et al.  Effect of poloidal density variation of neutral atoms on the tokamak edge. , 2002, Physical review letters.

[11]  E. D. Fredrickson,et al.  Recent results from the National Spherical Torus Experiment , 2003 .

[12]  L. L. Lao,et al.  The national spherical torus experiment (NSTX) research programme and progress towards high beta, long pulse operating scenarios , 2002 .

[13]  D. Stutman,et al.  Impact of the wall conditioning program on plasma performance in NSTX , 2002 .

[14]  Glen A. Wurden,et al.  Gas puff imaging of edge turbulence (invited) , 2003 .

[15]  Y-K.M. Peng,et al.  Characteristics of the first H-mode discharges in the national spherical torus experiment. , 2002, Physical review letters.

[16]  J. Ahn,et al.  A review of plasma boundary phenomena in the mega ampere spherical tokamak , 2003 .

[17]  L. L. Lao,et al.  The resistive wall mode and feedback control physics design in NSTX , 2004 .

[18]  B. Leblanc,et al.  High-speed imaging of edge turbulence in NSTX , 2004 .

[19]  G. F. Counsell,et al.  H-mode plasmas in the MAST spherical tokamak , 2002 .

[20]  Y-K.M. Peng,et al.  Evolution and termination of H-modes in NSTX , 2002 .

[21]  M. Greenwald,et al.  Edge turbulence imaging in the Alcator C-Mod tokamak , 2001 .