Imaging of low-frequency fluctuations in dipole confined plasma

Two 16-channel photodiodes arrays have been constructed to image the structure of low frequency (0.5-10 kHz) fluctuations observed in the LDX plasmas. Fluctuations in the 1-10 kHz range have previously been observed in LDX plasmas created with the internal coil supported [2]. We now report on observations of plasmas with the internal coil fully levitated. Fluctuations in this frequency range are still observed during multi-frequency heating and in addition fluctuations on the order of a few hundred Hz are also observed during 2.45 GHz only heating. Data from the 4-channel interferometer suggests these modes have some broad radial structure and electrostatic probes and Mirnov coils indicate an m=1 toroidal mode structure. The photodiode arrays will provide better radial resolution while simultaneously providing a measure of the toroidal mode number. A Phantom fast camera also images the plasma and we will compare results from the photodiode array to images from the fast camera. 2. Garnier et al, ``Stabilization of low frequency instability in a dipole plasma,'' to be published in Journal of Plasma Physics (2008).