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An additional magnetic field component was tested to try to stabilize the hot spot location in Hybrid X-pinch experiments on 250 kA - 1.2 MA pulsers. Three configurations of magnetic field have been experimentally tested. The most promising appeared to be the "cusp" configuration developed by pin electrodes twisted in opposite directions adjacent to the hybrid X-pinch in the diode of the pulser. [ABSTRACT FROM AUTHOR]

We present preliminary experimental results on mitigating Magneto-Rayleigh-Taylor (MRT) instabilities by applying an external Bz field. The experiments were conducted on the 1-MA, 200-ns COBRA generator at Cornell University. In the experiments, a triple-nozzle was used to produce z-pinch loads from concentric outer and inner annular gas puffs and a center gas puff column. A single coil was used to produce a Bz field in the pinch region. We have used two 4-frame 2-ns gated EUV cameras to obtain images of the imploding plasmas, in which the MRT instabilities were observed. The MRT instabilities can grow when the plasma accelerates toward the axis. With a triple gas puff (outer, inner and center puff), reduced acceleration or de-acceleration of the imploding plasma occurred when the outer puff plasma imploded onto the inner annular puff plasma resulting a relatively stable implosion. In the absent of the inner annular gas puff, the imploding outer annular plasma continued to accelerate toward the axis. Large turbulent flares at the edge of the implosion or pinch plasma were observed. The implosion was not stable. To stabilize the implosion without the inner gas puff, a Bz field was applied. This external Bz field was compressed by the outer imploding plasma shell. A relatively stable implosion was observed. Increasing the Bz field to 2-kG resulted in a relatively fatter pinch plasma. [ABSTRACT FROM AUTHOR]

The current results on the large UCLA Electric Tokamak (ET, R = 5 m, a =1 m) indicate that its potential for ICRF heating and current drive is sufficiently robust to explore plasma stability beyond the Troyon limit up to the unity beta regime. The achievement of unity beta plasmas requires virtually steady state, non-inductive plasmas with an energy confinement time of about 1 second. Due to the large volume of ET (150 m³), the Ohmic plasma confinement is excellent (a central energy confinement time of 350 msec has been achieved) and we estimate that the anomalous electronic heat conduction will not be a limiting factor for high beta exploration. In this paper we will present the current status of the ICRF experiments and the realization of excellent antenna loading using water-loaded couplers in the range of 1 to 10 MHz. The goal is to achieve unity beta plasmas by ICRF heating and current drive, relying on a large bootstrap current fraction. The reactor related aspects of this research are very exciting, provided a deep second stable plasma core can be produced by ICRF-based techniques. [ABSTRACT FROM AUTHOR]