SELF-ORGANIZATION AND ITS EFFECT ON CONFINEMENT IN A REVERSED-FIELD PINCH PLASMA

Results of self-organization of the magnetic field and associating pla sma loss are reviewed in the reversed field pinch (RFP) experiments on TPE machines. It is shown that the RFP plasma has a strong tendency t o relax to a certain magnetic configuration similar to the energy mini mum state predicted by Taylor. Thus the RFP configuration is self-orga nized and self-sustained with appropriate control of experimental cond itions. Interestingly, however, it is observed in some cases that the relaxation can take place without the conservation of total magnetic h elicity. The mechanisms of the self-organization and associated loss a re discussed in some detail. In the low pinch parameter region (<1.6), the self-organization is continuous and the main loss mechanism seems to be the electron motion along the stochastic magnetic field line ca used by the overlapping of multiple modes of the magnetic fluctuations being excited Simultaneously. In the high pinch parameter region, sel f-organization is characterized by the pulse-like relaxation (intermit tent in many cases), which seems to destroy the magnetic surface in a certain position of the torus and causes rapid loss of plasma energy. Attempts to improve RFP confinement by controlling the relaxation are described. One example is the improved high-theta mode in TPE-1RM20 an d another is the pulsed poloidal current drive in MST.