Power absorption of the plasma in high-frequency discharge are investigated. As a result, two peaks of the absorbed power are observed with regard to gas pressure. One peak can be explained by the increase of positive conductance of the plasma. Another peak can be explained by the appearence of a negative conductance which causes by the interaction between radial electron diffusion velocity and axial high-frequency magnetic field. Moreover, the effects of external magnetic field and microwave incidence upon this negative conductance are investigated.
A step response of a plasma column to the desired plasma position is examined for several types of feedback control by solving the equation of motion of a plasma column in a resistive shell. Experimental results in JIPP T-II are also described.