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

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%.