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Low-Energy Neutral Spectroscopy During Pulsed Discharge Cleaning in PLT

Published in 1983

J. Vac. Sci. Technol., A 1, 818-821 (1983)

Ruzic, D. N., Cohen, S., Denne, B., Schivell, J.

The efflux of neutral hydrogen from PLT during discharge cleaning has been measured using a time-of-flight spectrometer. During high ionization pulsed discharge cleaning (PDC), the flux in the energy range of 5 to 1000 eV varies from 1014 H0/cm2·s to 1016 H0/cm2·s and the average energy from 10 to 80 eV. The energy distributions are nearly single temperature Maxwellians. Low ionization PDC (Taylor-type) produces a 1000 times lower fluence in the same energy range; however, a flux of 1016 H°/cm2·s at energies less than 5 eV is inferred. The detailed submillisecond time variation of these parameters with the fill gas pressure and state of cleanliness of the machine is presented. Comparisons with UV spectroscopy, bolometric measurements, and residual gas analysis are made.

Perturbation of Tokomak Edge Plasma by Laser Blow-Off Impurity Injections

Published in 1983

J. Vac. Sci. Technol., A 1, 837-840 (1983).

Budny, R., Cavallo, A., Cohen, S., Daughney, C., Efthimion, P., Fonck, R., Hulse, R., Hwang, D., Manos, D., Pequet, A.-L., Ruzic, D. N., Schivell, J., Smith, B., Yelle, R.

We describe measurements of tokamak edge plasma perturbations caused by rapid injection of impurities such as Sc, Fe, and Mo into Ohmically heated PLT discharges. The temporal evolution of the radiated power, convected power, charge-exchange neutral flux, electron temperature, density, and floating potentials were monitored using recently developed fast bolometers, directional calorimeters, and other diagnostics. The central radiated power can be doubled without plasma disruptions. Radiation from the edge then increases tenfold for ~2 ms. Neutral efflux at the limiter decreases up to two orders of magnitude for approximately 20 ms after injection. The electrical potential of the limiters increases, approaching the potential of the vacuum vessel. MHD activity in the m=1 (sawtooth) mode tends to increase while that in the m=2 and m=3 modes decreases. The power flowing along field lines in the limiter shadow region sometimes increases or sometimes decreases by more than a factor of 4. The density and electron temperature in the limiter shadow region, generally, does not change more than 50%.