X-ray tomography and potential studies in GAMMA 10

Relation between electron behaviours and plasma potentials is investigated using X-ray tomographic reconstruction techniques; such temporal and spatial measurements are essential to plasma confinement studies. In this paper, the first application of two sets of 50-channel microchannel plates has been carried out using their detailed calibration data as a function of X-ray energy and incident angle. In the thermal barrier region, axisymmetric 60-keV hot electrons and an axisymmetric potential profile with heavy ion (Au deg.) beam probes are observed to be peaked on the magnetic axis. These are found to be desirable for the formation of the thermal barrier potential in the core plasmas as well as for a good plasma confinement because of avoiding the formation of a localized anisotropic electric field, which may enhance a radial nonambipolar transport. Furthermore, a combination of such spatial X-ray diagnostics and X-ray energy spectrum observations solves the potential formation mechanism in the plug region. The first observation of a plateau-shaped plug electron velocity distribution function has been carried out; this result is consistent with Cohen's strong electron cyclotron heating theory. A drastic improvement in an ion confinement time is, in turn, found due to the formation of these kV-range plug potentials by using temporally and spatially resolved end-loss-ion analysers. (author). 22 refs, 9 figs