Control device for the surface position of plasma

Purpose: To measure the surface position of divertor-arranged plasmas at a high accuracy of less than 1 mm second and further conduct feed back control. Constitution: From signals of more than three rows of magnetic measuring instruments, each row consisting of three or more instruments arranged on one straight line and disposed near the null point of the divertor-arranged plasmas, values of a magnetic flux function at the null point, which is the spacial saddle point of the magnetic flux function, can be measured at a high accuracy. The thus calculated values of the magnetic flux function for the null point is the value of the magnetic flux function at the surface of the plasmas. The position at the surface of plasmas is measured by the signal from the magnetic measuring instruments disposed at the points for controlling the distance with the plasma surface and the value of the magnetic flux function at the surface of the plasmas. Current flowing through poloidal coils depending on the difference between the predetermined surface position of the plasmas and the actually measured surface position of the plasmas is controlled. In this way, feed back control for the position at the surface of plasmas at high speed (higher than 1 kHz) is enabled, thereby maintaining plasma discharges with good confining property. (Kamimura, M.)