Perturbed magnetic-field phase slip for tokamaks

Given a set of rotating helical current filaments within a cylindrical plasma and a set of fixed magnetic-field detectors at the edge of the plasma, a mathematical model is used to investigate the observable effect of rotation or longitudinal motion in the intervening plasma. If the soft-X-ray signals from magnetic islands indicate the instantaneous position of the helical current filaments within the plasma, then the phase difference between the X-ray signal and the magnetic fluctuations should provide a diagnostic of tokamak plasma rotation. The relative motion between the islands and the electron fluid is measured by the 'slip' S(r) = ω – kvz(r) – mvΘ(r)/r, where ω is the rotation frequency of the islands and is the electron fluid velocity. – The plasma velocity and the Hall effect are added to Rosenbluth's reduced equations to compute the phase difference between the island position and the perturbed magnetic field at the edge of the plasma as a function of the slip for a variety of resistivity profiles. The current profile within the islands is taken from the non-linear computer results of White, Monticello, Rosenbluth and Waddell. – Comparison with experiment indicates essentially locked electron fluid and mode motions, i.e. S(r) ≅ 0.