Soft x-ray and bolometric tomography in RFX

The article presents the design and the first results of a new eight camera, soft x-ray (SXR) and bolometric tomography which has been installed in RFX, a large (R = 2 m, a=0.46 m), high current reverse held pinch experiment operating in Padova. The main features of the diagnostic, which has been designed with standards compatible with the requirements of large fusion experiments, are: (a) it allows simultaneous reconstruction of both SXR and total radiation emissivity structures with high spatial and time resolution (bandwidth up to 200 kHz for SXR and 10 kHz for bolometry). Moreover, computer controlled remote actions which interchange up to five material filters in front of the detectors allow the exploration of different energy ranges; (b) it can be easily decoupled from the machine without breaking the main vacuum and can be operated during first wall baking up to 300 degrees C thanks to a cooling circuit; (c) the detection chain is designed to measure very low signals [in the order of 1 nA for SXR diodes and of 100 mu V for bolometers]; (d) it is equipped with a VME based 1 MHz data acquisition system which allows on-line processing of a large amount of data. To accomplish these features the diagnostic consists of eight fully remotely controlled manipulators which can insert eight photocameras, carrying 78 top-rated Si SXR and 48 miniaturized metal firm bolometric detectors in their operating positions. Initial results are presented.