The effect of electric fields and pitch-angle scattering on the radial neutral flux

The radial flux of 10 keV neutrals from the Asdex-Upgrade tokamak has been interpreted as a diagnostic of the radial electric field Er near the plasma edge (Herrmann W and Asdex-Upgrade Team 1995 Phys. Rev. Lett. 75 4401), with the conclusion that Er changes gradually at a transition from the L-mode confinement regime to the H-mode regime. In contrast to the Asdex-Upgrade results, a similar installation on the DIII-D tokamak finds no measurable signal in H-mode plasmas with deep Er wells. Measurable signals only occur in plasmas with relatively large pitch-angle scattering rates at the plasma edge (or with anomalous beam-ion confinement). Large scattering rates require a large electron temperature and are invariably accompanied by deep ripple wells. The results suggest an alternative explanation for the gradual evolution of the neutral-particle signal from Asdex-Upgrade: as the H-mode pedestal develops, more beam ions are pitch-angle scattered into the phase space measured by the detector.

[1]  On the modelling of fast particle ripple losses in tokamaks , 1994 .

[2]  R. Kaita,et al.  Characteristics of compact solid‐target charge exchange analyzers for energetic ion diagnostics on tokamaks , 1987 .

[3]  W. Heidbrink,et al.  ARRAY OF NEUTRAL PARTICLE ANALYZERS AT DIII-D , 1996 .

[4]  Taina Kurki-Suonio,et al.  Fast response in the ripple trapped ion distribution to abrupt changes in a radial electric field in tokamaks , 1998 .

[5]  Masaki Osakabe,et al.  High Ion Temperature Mode in CHS Heliotron/torsatron Plasmas , 1997 .

[6]  R. Budny,et al.  Study of thermonuclear Alfvén instabilities in next step burning plasma proposals , 2003 .

[7]  Herrmann.  Radial electric fields during L-to-H transition and edge-localized modes from charge-exchange diagnostics of Ripple-trapped particles. , 1995, Physical review letters.

[8]  R. J. Groebner,et al.  Scaling studies of the high mode pedestal , 1998 .

[9]  L. Lao,et al.  Reconstruction of current profile parameters and plasma shapes in tokamaks , 1985 .

[10]  W. Herrmann.  Diagnostic method for radial electric fields in Tokamaks by the observation of ripple-trapped ions , 1998 .

[11]  J. L. Luxon,et al.  Big Dee - A Flexible Facility Operating Near Breakeven Conditions , 1985 .

[12]  F. Wagner,et al.  Regime of Improved Confinement and High Beta in Neutral-Beam-Heated Divertor Discharges of the ASDEX Tokamak , 1982 .

[13]  S. Coda,et al.  Constraints on theories provided by fast time response measurements across the L to H transition on DIII-D , 1996 .

[14]  W. Heidbrink,et al.  Measurements of the neutron source strength at DIII-D , 1997 .

[15]  Taina Kurki-Suonio,et al.  The Effect of a Radial Electric Field on Ripple-Trapped Ions Observed by Neutral Particle Fluxes , 1997 .

[16]  L. L. Lao,et al.  Direct Measurement of the Radial Electric Field in Tokamak Plasmas using the Stark Effect , 1997 .

[17]  Wade,et al.  Rotation characteristics of main ions and impurity ions in H-mode tokamak plasma. , 1994, Physical review letters.

[18]  Burrell,et al.  Role of edge electric field and poloidal rotation in the L-H transition. , 1990, Physical review letters.

[19]  L. L. Lao,et al.  SIMULTANEOUS MEASUREMENT OF Q AND ER PROFILES USING THE MOTIONAL STARK EFFECT IN HIGH-PERFORMANCE DIII-D PLASMAS (INVITED) , 1999 .

[20]  Taina Kurki-Suonio,et al.  Ripple-trapped beam ions in the presence of a radial electric field , 1998 .

[21]  T. N. Carlstrom,et al.  Real-time, vibration-compensated CO2 interferometer operation on the DIII-D tokamak , 1988 .

[22]  K. Burrell,et al.  High spatial and temporal resolution visible spectroscopy of the plasma edge in DIII‐D , 1990 .

[23]  R. Bell,et al.  Turbulent edge transport in the Princeton Beta Experiment‐Modified high confinement mode , 1994 .

[24]  K. H. Burrell,et al.  Effects of E×B velocity shear and magnetic shear on turbulence and transport in magnetic confinement devices , 1997 .

[25]  W. Heidbrink,et al.  CORRIGENDUM: The behaviour of fast ions in tokamak experiments , 1994 .

[26]  T. Kurki-Suonio,et al.  The time behaviour of radial electric fields at the L-H transition from the observation of ripple-trapped ions , 1998 .

[27]  K. Burrell.  Tests of causality: Experimental evidence that sheared E×B flow alters turbulence and transport in tokamaks , 1999 .

[28]  W. Heidbrink,et al.  What is the “beta-induced Alfvén eigenmode?” , 1999 .

[29]  T. H. Stix,et al.  Heating of toroidal plasmas by neutral injection , 1972 .

[30]  R. Groebner,et al.  Measurement of neutral density near the X point in the DIII-D tokamak , 2000 .

[31]  J. Hugill.  REVIEW ARTICLE: Edge turbulence in tokamaks and the L-mode to H-mode transition , 2000 .

[32]  S. Coda,et al.  Beyond paradigm: Turbulence, transport, and the origin of the radial electric field in low to high confinement mode transitions in the DIII-D tokamak , 1995 .

[33]  G. L. Campbell,et al.  Design and operation of the multipulse Thomson scattering diagnostic on DIII‐D (invited) , 1992 .

[34]  K. Burrell.  Diagnostics for advanced tokamak research (invited) , 2001 .

[35]  H. Zohm,et al.  Ion orbit loss current in ASDEX upgrade , 1998 .

[36]  Taina Kurki-Suonio,et al.  Analysis of the tokamak ripple-blocked ion distribution with abrupt changes of a radial electric field , 1998 .