X-ray emission fluctuations from the HBTX1A reversed field pinch have been investigated with an array of silicon surface barrier diodes using statistical analysis techniques. Despite their apparent randomness a new correlation technique involving all the signals has been used to identify the dominant activity at frequencies <or approximately=20 kHz as global modes with poloidal mode number m=0 and 1. This technique also allows the reconstruction of the radial profile of the modes and the calculation of their power spectrum. By using single detectors displaced in the toroidal direction it is shown that the m=0 instabilities have long toroidal wavelength (n approximately 0) and do not propagate in this direction, whereas the m=1 modes have n>>1. Local turbulence becomes the dominant component at higher frequencies; even so correlation lengths parallel to B are much longer than across. Correlating the X-ray diodes with magnetic edge coils enables a direct comparison of the two types of fluctuations and shows that one of the m=0 modes propagates radially outwards.
Resistive g-modes in a reversed-field pinch plasma