Stability criteria for currentdriven drift wave eigenmodes
Abstract
Eigenmodes of currentdriven collisionless electrostatic drift waves in a sheared magnetic field are reexamined in the light of the recent discovery that their noncurrentdriven counterparts are stable. Conditions for instability are determined from numerical finite difference and variational solutions of the slab model differential equation. It is found that three stringent conditions are required for instability: (1) very weak shear, (2) low ion temperature, and (3) very large parallel drift velocity. For L_{n}/L_{s}=0.02 and T_{i}/T_{e}=0, the instability threshold is u_{d}/c_{s}=0.85, where L_{n} and L_{s} are the density and shear scale lengths, respectively, u_{d} is the drift velocity, and c_{s} is the sound speed. For larger shear and finite ion temperature the critical drift velocity is even larger. It is concluded that drift wave fluctuations in tokamaks cannot be described in terms of these eigenmodes.
 Publication:

Physics of Fluids
 Pub Date:
 February 1979
 DOI:
 10.1063/1.862580
 Bibcode:
 1979PhFl...22..294R
 Keywords:

 Collisionless Plasmas;
 Drift Rate;
 Electrostatic Waves;
 Magnetohydrodynamic Stability;
 Propagation Modes;
 Tokamak Devices;
 Energy Technology;
 Finite Difference Theory;
 Ion Temperature;
 Magnetic Field Configurations;
 Plasma Control;
 Plasma Density;
 Variational Principles;
 Wave Functions;
 Plasma Physics