Plasma current in tokamak conditions: An application of the guiding field line model

A new kinetic representation for the plasma current is examined for tokamak conditions. Within this representation, the periodic bounce motion is extracted from the guiding center motion of particles. The drift orbit of a guiding center is viewed as a closed loop stretched along the guiding field line-a field line that moves at the bounce-averaged drift rate. Because all quantities, including the distribution function, are defined not on the basis of the particle's guiding center, but rather on the basis of the guiding field line, an additional magnetization term appears, which corresponds to the wobbling deviation of the guiding center from the guiding field line. Thus, the current is decomposed into three terms: The flow of orbits as a whole, the gyro-magnetization, and bounce-wobble magnetization. The great advantage of the new model is that the zeroth-order distribution function, a nonshifted Maxwellian distribution, yields a current that satisfies the fluid equations. (C) 2000 American Institute of Physics. [S1070- 664X(00)02910-4].