The skin effect and its relaxation in tokamak LT-3

Abstract

A hollow current profile is observed to form in the early stages of the Canberra tokamak LT-3. A helical perturbation appears, of the mode predicted by resistive MHD theory (m = 4, n = 1) for the measured q-profile. Subsequently, the plasma relaxes rapidly to a state of approximately uniform current. Runaway electrons diffuse very rapidly during this period with step sizes round the torus of up to 1 cm. These are indicative of a disruption of the magnetic surfaces, probably as a result of the growth of the helical perturbation.

Compound sawtooth study in ohmically heated TFTR plasmas

“…This suggests the existence of a flat or slightly hollow current profile even during a steady state, especially in high current and/or high density operation [7]. However, even if hollow current profiles were common in earlier tokamaks [15], no compound sawteeth were observed. The reason could As mentioned in Sec.…”

Wall interaction of tearing modes in configurations with multiple rational surfaces

“…These cases are associated with hollow current profiles. Such profiles arise in tokamaks during the startup phase [15] and possibly also during disruptions [16, 171. We use the singular boundary layer approach [I], where the plasma is divided into two types of regions. In the outer regions, away from the rational surfaces, resistivity can be neglected, while in the inner regions about the rational surfaces we use the analytical expressions of Ref.…”

Impurity sources during lower hybrid heating on Alcator

“…The magnitude of this tail heat flux can be roughly estimated by comparing the slowing-down time of the fast electrons (E « 30-40 keV) on the bulk plasma (r ee « 0.5 ms) with their diffusive energy confinement time, r tai] . The energy confinement times of higher energy electrons in other tokamaks [3,9,10,11], as well as those in Alcator C at lower n e [12], have been measured to be approximately equal to the energy confinement time of electrons in the bulk plasma. Therefore, given that the energy confinement time of both higher energy (MeV) electrons and bulk electrons is of the same order, it can be assumed that the energy confinement time of medium energy electrons (30-50 keV) is also the same (r tail « 10 ms).…”