A multichord soft x-ray diagnostic for electron temperature profile measurements in RFX-mod

We report on the design and first results obtained with a multichord diagnostic for the measurement of the electron temperature profiles in RFX-mod. The diagnostic consists of four groups of five photodiodes each, measuring the soft x-ray plasma emissivity through four pinholes. Each pinhole houses a beryllium filter with different thickness. The 20 lines of sight defined by the diodes and the pinholes, emanating from the same porthole and looking at the same poloidal section, are coupled two by two. This results in a fan of ten pairs of chords covering the outboard section of the RFX-mod plasma. The double-foil technique applied to each pair of chords allows for the estimation of the electron temperature. The spatial resolution of the diagnostic permits to detect detailed features of the electron temperature profiles with a high time accuracy: the several kilohertz bandwidth electronic system allows for following in time the plasma dynamic evolution. Comparisons of the estimated T-e with the Thomson scattering diagnostic and with the on-axis multifoil spectrometer are also reported. (c) 2006 American Institute of Physics.