Fast Camera Analysis of the PFRC-2 Instabilities and Mode Structures

Long-lived plasma pulses formed in the PFRC-2 are vulnerable to a wide range of instabilities. Radial line-average density measurements have shown saturated low frequency modes, 5-100 kHz, in the range expected for low-m interchange modes and drift-wave instabilities. Herein we report on expanded axial view of the entire cross section of PFRC-2 H, He, Ne, and Ar plasmas, obtained with a Phantom v7.3 fast camera (140,000 fps). The behavior of coherent radial and azimuthal structures – primarily low-m spokes seen in the visible light – were tabulated as a function of the following parameters: RF plasma heating power, vacuum axial B-Field, fill gas pressure and species, and transverse cusp-field (Ioffe bars) strength. The spokes were seen to flutter, rotate, and vary in thickness. Major changes were seen in the direction of spoke rotation, the amplitude of high-m (~ 100) modes, the spoke turbulence spectrum, and magnetic shear at large radius. The effect of H gas puffs on the spokes was investigated.