Shear stabilizing experiment of gun-spheromak plasma (CTCC-I)

In a gun-spheromak experiment (CTCC-I), the plasma is cleaned of impurities by titanium coating on the flux conserver (FC) wall, becomes active and sometimes suffers from disruptive termination. To overcome the disruptive instability, it is tried to insert a central conductor along the geometric axis of the FC, which is expected to have a higher magnetic shear configuration. Results demonstrate a suppression of the disruptive instability, but a rather weak instability remains, the so-called stepwise instability. Magnetic-field measurements show spatial differences in the field decay, probably due to an inhomogeneity in the plasma resistivity. The equilibrium configuration of CT is hence interpreted as one that changes into a configuration with a rather peaked current profile, resulting in the stepwise instability. OV line (2781 A) radiation and the average density show a sawtooth and a stepwise waveform, respectively. Moreover, the change in the plasma behaviour is examined by using conductors with different diameters. The results show that larger diameters of the conductor make the plasma more stable. (author)