IMPROVED CONFINEMENT IN A HIGH PINCH PARAMETER REGION OF THE REVERSED-FIELD PINCH PLASMA

Discharges with improved plasma confinement in a high pinch parameter region (Theta similar to 2) have been discovered in the TPE-1RM20 reve rsed field pinch experiment. These discharges become possible with car eful control of the waveforms of the plasma current and the toroidal m agnetic field after intensive discharge cleaning and are called the 'I mproved High Theta Mode' (IHTM). In these discharges the increase of e lectron density is distinct when compared with low Theta cases (simila r to 1.55). The electron temperature increases slightly with Theta but the ion temperature remains almost constant. Consequently, the poloid al beta increases, from 8% at Theta similar to 1.55 to 18% at Theta si milar to 2.0, and the energy confinement time increases from 0.2 to 0. 4 ms. The fluctuation level of the magnetic field corresponding to the dynamo activities is reduced by about a factor of 3 in IHTM, which ma y explain this improvement. Possible causes of IHTM are discussed. It is Found that the m = 1 mode rotates continuously during IHTM, while i t always stops rotating just before a large soft X ray emission crash occurs.