Runaway snakes in TEXTOR-94

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Abstract
Observations of a runaway beam confined in an island-like structure, a so-called runaway snake, are reported. The observations are made in TEXTOR-94 by measurement of synchrotron radiation emitted by these runaways. A full poloidal view allows for the study of the synchrotron pattern of the snake to estimate runaway energy, pitch angle and the radius, shift and safety factor of the drift surface qD at which the runaway beam has developed. The runaway snake parameters are investigated under different current and magnetic field strength conditions. Examples are found of a runaway snake at the qD = 1 and the qD = 2 drift surface. The radial diffusion coefficient of runaways inside a snake is . The rapid runaway losses in regions of (macroscopic) magnetic perturbations outside a snake and the good confinement inside an island assumed to consist of perfect nested surfaces are consistent with magnetic turbulence as the main cause for runaway transport.