ROLES AND PRODUCTION MECHANISM OF ENERGETIC PARTICLES AT SELF-ORGANIZATION IN REP

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The purpose of the present research is to obtain some insights into production mechanism of energetic particles in STE-2 RFP at Kyoto Instute of Technology. During the first year, an X-ray probe, consisting of a metal target and a surface barrier diode with polyester filters, was constructed. And, at the same time, effects of the proximity of conducting shell (b/a, where b and a are the plasma and shell minor radii, respectively) on REP plasma performance were studied for improving the RFP discharges. It was found that discharge resistance decreased by a factor of 2 with an improved shell proimity (b/a=1.07(] SY.scharw.[)1.02). During the following year, energetic electron studies were performed with the X-ray probe in STE-2 with the close fitting shell. The major results obtained are as follows: (i) We have observed non-thermal electrons with energies around 400-500 eV, much higher than the bulk electron temperature of 40-50 eV, in the edge region r/a>0.7. (ii) The energetic electrons flow along the magnetic field line in the sense that they are accelerated by the Ohmic electric field in the central region. (iii) The energetic electron density decreases with an increase in fill pressure. The pressure dependence of the energetic electron density is the first observation in RFP's. Thus, a detailed comparison of the results with theoretical models of production mechanism of fast electrons is beneficial to understanding the RFP plasma dynamics. We have also made an estimate for applying the technique of an electromotive force (EMF) probe which is a combination of a directional probe and a magnetic pickup coil. It has been found that under certain plasma conditions, we can estimate the magnetohydrodynamic (MHD) dynamo term <vxB> with this probe.