The generalized accessibility and spectral gap of lower hybrid waves in tokamaks

The generalized accessibility of lower hybrid waves, which may include shifting of the parallel refractive index (n∥), either upward or downward, is investigated, using the cold plasma dispersion relation and various geometrical constraint (GC) relations imposed on the behavior of n∥. It is shown that n∥ upshifting is bounded and can be insufficient to bridge a large spectral gap to cause wave damping, if the GC relation does not allow the oblique resonance to occur. The traditional n∥ upshift mechanism based upon the pitch angle of magnetic field lines is shown to lead to contradictions with experimental observations. An upshift mechanism brought about by the density gradient along field lines is proposed, which is not inconsistent with experimental observations, and provides plausible explanations to some unresolved issues of lower hybrid wave theory, including generation of ‘seed electrons.’

[1]  J. Manickam,et al.  Experimental exploration of profile control in the Princeton Beta Experiment-Modified (PBX-M) tokamak , 1993 .

[2]  Parker,et al.  Gyrokinetic simulation of ion temperature gradient driven turbulence in 3D toroidal geometry. , 1993, Physical review letters.

[3]  Paul,et al.  Long-wavelength density turbulence in the TFTR tokamak. , 1993, Physical review letters.

[4]  M. Porkolab,et al.  Lower hybrid heating in the Alcator A tokamak , 1981 .

[5]  Tadashi Sekiguchi,et al.  Plasma Physics and Controlled Nuclear Fusion Research , 1987 .

[6]  T. H. Stix.  Radiation and absorption via mode conversion in an in homogeneous collisionfree plasma. , 1965 .

[7]  K. Kupfer,et al.  Wave chaos and the dependence of LHCD efficiency on temperature , 1992 .

[8]  M. Brambilla,et al.  Slow-wave launching at the lower hybrid frequency using a phased waveguide array , 1976 .

[9]  D. Ignat.  Toroidal effects on propagation, damping, and linear mode conversion of lower hybrid waves , 1981 .

[10]  F. Crisanti,et al.  Density limit for lower hybrid wave-electron interaction and minority hydrogen absorption in FT , 1984 .

[11]  G. Vahala,et al.  Effect of magnetic and density fluctuations on the propagation of lower hybrid waves in tokamaks , 1992 .

[12]  Sverdrup Lh,et al.  Cause of the lower-hybrid current-drive density limit. , 1987 .

[13]  Paul Bonoli,et al.  Linear Theory of Lower Hybrid Heating , 1984, IEEE Transactions on Plasma Science.

[14]  Nathaniel J. Fisch,et al.  Theory of current-drive in plasmas , 1987 .

[15]  F. Perkins,et al.  Scattering of lower‐hybrid waves by drift‐wave density fluctuations: Solutions of the radiative transfer equation , 1983 .

[16]  M. Porkolab.  Survey of Lower Hybrid Experiments , 1984, IEEE Transactions on Plasma Science.

[17]  Edward Ott,et al.  Toroidal and scattering effects on lower‐hybrid wave propagation , 1982 .

[18]  T. H. Stix.  Waves in plasmas , 1992 .

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

[20]  N. Fisch.  Confining a Tokamak Plasma with rf-Driven Currents. , 1978 .

[21]  E. Ott,et al.  Wave reflection from the lower hybrid surface: A toroidal effect , 1979 .

[22]  Observation and analysis of a two-parallel-temperature electron tail during lower-hybrid current-drive on a tokamak , 1993 .

[23]  A. Bers,et al.  Waves in anisotropic plasmas , 1963 .

[24]  S. Wolfe,et al.  Marfe: an edge plasma phenomenon , 1984 .

[25]  E. Mazzucato,et al.  Scaling of density fluctuations in PDX , 1985 .

[26]  R. Parker,et al.  TRANSPORT OF rf ENERGY TO THE LOWER HYBRID RESONANCE IN AN INHOMOGENEOUS PLASMA. , 1972 .

[27]  T. H. Stix,et al.  The Theory Of Plasma Waves , 1962 .

[28]  Edward Ott,et al.  Ergodic behavior of lower hybrid decay wave ray trajectories in toroidal geometry , 1978 .

[29]  T. K. Chu,et al.  Top-versus-side launch of lower hybrid waves in PLT , 1986 .

[30]  Charles F. F. Karney,et al.  Numerical studies of current generation by radio‐frequency traveling waves , 1979 .