Simulation of ECR Startup and Comparison with Experimental Observations in SUNIST

Transient process of ECR startup in SUNIST with a one-dimensional model is analyzed and simulated. Contributions from the generation, drift, diffusion and loss of electrons are taken into account in the model and estimated from experimental parameters, e.g., toroidal field, vertical field and gas filling pressure. Typical discharges are simulated with the conditions close to the experiomental ones. Both experimental and simulated results are comparable qualitatively in amplitudes and semi-quantitatively in time. From the results it is confirmed that the transient process of ECR startup in SUNIST is dominant, as preliminarily deduced from experimental observations, by a pair of exclusive factors, namely the absorption, due to gas ionization, and the reflection of microwave, caused by the shift of over dense plasmas due to outward E×B drift. In addition to these two factors, electron loss along the field line is also very important in determining the character of discharges.