Production of Over-Dense Plasmas by Launching of 2.45 GHz Electron Cyclotron Waves on the Compact Helical System

A simulation experiment of high temperature plasma transport using low temperature plasma having dimensionless parameters similar to those of a high temperature plasma is currently underway in the Compact Helical System. To produce such a plasma, 2.45 GHz microwaves up to 20 kW were injected perpendicularly to the toroidal field at Bt < 0.1 T. In the case at Bt = 0.0613 T, the maximum electron density reached three times that of the O-mode cutoff density. The measured power deposition was localized in the plasma core region beyond the Left-hand cutoff layer. These results clearly suggest that the over-dense plasma was produced and heated by electron Bernstein waves converted from launched X-mode in the peripheral region with a steep density gradient.