X-VUV spectroscopic imaging with a micropattern gas detector

An innovative system which combines very fast 2D imaging capabilities with spectral resolution in the X-VUV range 0.2–8 keV has been developed at ENEA-Frascati (Italy) in collaboration with INFN-Pisa (Italy). It is based on a pinhole camera coupled to a micropattern gas detector having a gas electron multiplier as gas amplifying stage. This detector (2.5 cm×2.5 cm active area), equipped with a 2D read-out printed circuit board with 144 pixels in a square matrix geometry (12×12) has been adapted to work at low energy, as far as 0.2 keV, in various configurations. Spectra with different X-VUV laboratory sources, energy calibrations curves and detection efficiency are discussed for all the proposed configurations. Thanks to the high photon flux (106 ph/s mm2) detected by this device, high time resolution can be obtained (framing rates up to 100 kHz). The full system has been tested on the Frascati Tokamak Upgrade in 2001 and on the National Spherical Tokamak eXperiments (NSTX) in 2002 as a possible diagnostic tool for magnetic fusion plasmas. Time-resolved 2D images are presented. These results open the way to a new X-VUV imaging technique, where the low definition (limited number of pixels) is highly compensated by the strongly enhanced contrast due to the fine and controlled energy discrimination and by the capability to get images in a selected energy range. The innovative combination of these two major characteristics, make this device a candidate for applications beyond the magnetic plasma physics field.