X-ray tomography on IR-T1 tokamak

Summary form only given, as follows. Measurements of soft X-ray emission from the IR-T1 tokamak plasma have been analysed with tomographic reconstruction methods. IR-T1 is a small air core transformer tokamak with circular cross-section and without copper shell and divertor (R=45 cm, a=12.5 cm, Bt<1 T, Ip=20-40, Ne=(0.7-2.5)/spl times/10/sup 1/3 cm/sup -/3, Te=150-200 eV). The detector system is on a circular are view IR-T1 tokamak plasmas through a thin beryllium window (in a fashion similar to that of a pin-hole camera), to provide poloidal imaging of soft X-ray emission (SXR) in the 600 eV-20 keV range. Each detector has an active area 3/spl times/20 mm/sup 2/. The signals are digitized every 4 /spl mu/s or 8 /spl mu/s by use of 8 bit transient recorders and the frequency response of detector-preamplifier system is from 10 Hz-200 kHz. The tomography method (Cormack's method) is used for reconstructing the images of SXR emissivity distribution in the poloidal cross-section of IR-T1 tokamak. X-ray imaging (XIS) diagnostics of the sawtooth oscillation have tended to emphasize the coincidence between magnetic surfaces and the contours of equal X-ray emissivity. Because there is a detector array, one-dimensional images of SXR emissivity are obtained without having to resort to rotation models. This method has been used to study the internal disruptions and m=1 oscillation. The reconstructed images in the phase before a sawtooth crash have shown the hot plasma core move gradually toward one side, this is considered that as the increasing m=1 kink mode.