Investigation of Edge Neutral Flux on the ISX-B Tokamak Using a Low-Energy Charge-Exchange Analyzer

摘要

To study the emission of D exp 0 from the periphery of a tokamak plasma, a low-energy neutral particle spectrometer optimized for (16 < E < 500 eV) has been built and employed on the Impurity Study Experiment (ISX-B) tokamak. The diagnostic utilizes a cesium vapor cell to form negative ions from the incident D exp 0 neutrals and a four-channel electrostatic analyzer to energy analyze the negative ions. The spectrometer was absolutely calibrated using D exp 0 beams formed by electron capture by positive ions in a gas cell and by photo-detachment of negative ions by a yttrium-aluminum-garnet laser. For the observation region chosen on ISX-B (120 exp 0 toroidally away from the limiter, near the gas puff), the neutral particle flux has a two-component nature. These data are well fit by two separate exponential distributions of equivalent temperatures 6 to 8 eV for particle energies below about 80 eV and 70 to 80 eV for particle energies above 80 eV. For ohmically heated discharges, the measured particle flux in the energy range 25 to 700 eV is approx. 2.5 x 10 exp 15 cm exp -2 .s exp -1 ; the mean particle energy is approx. 70 eV, and the calculated flux at the wall is approx. 30 mW/cm exp 2 . The major effect of neutral beam heating is to increase the particle flux in the 25- to 700-eV range by a factor of 3. (ERA citation 08:050378)