The equilibrium control experiment on TPE-1RM15

The DC vertical field system is used with the conducting shell in order to control plasma equilibrium position in TPE-1RM15 reversed field pinch machine. If the equilibrium of plasma is maintained only by the conducting shell, the magnetic axis of plasma column shifts against the center of poloidal cross section of the shell. Then plasma interacts locally and strongly with the wall of vacuum vessel which is set concentrically in the conducting shell. Due to these interactions the light impurities like oxygen and heavy metal impurities like iron are ejected into plasma. These impurities may decrease energy confinement time of plasma because of the additional radiation loss. When we switch on the DC vertical field and adjust the outher magnetic surface of plasma to the wall surface, we can make the interaction between plasma and wall of vacuum vessel or limiter nonlocal and week. The experiment in which we control the equilibrium position of plasma correctly (in optimum way), as compared with no control case shows the increase of confinement time by a factor of two. In these way the plasma confinement properties were remarkably improved. (author)