Development of double-foil soft X-ray array imaging (DSXAI) diagnostic on HL-2A tokamak

A 100-channel double-foil soft X-ray array imaging (DSXAI) diagnostic system has been developed for the HL-2A tokamak to obtain tomographic bremsstrahlung emissivity and electron temperature (T_e). This system employs a double-foil technique to determine T_e by comparing the soft X-ray (SXR) emissivities from the same plasma location through two Beryllium (Be) foils of differing thickness. The DSXAI system comprises five photocameras mounted at two different poloidal cross-sections, separated toroidally by 15°, allowing for three distinct poloidal viewing angles. Each photocamera features 20 channels, offering a temporal resolution of approximately 4 μs and a spatial resolution of about 8 cm, with no channel overlap. Each photocamera contains two identical optical systems, each defined by an aperture slit and a photodiode array. The double-foil configuration is realized by placing these two optical systems, each with a different Be foil, in close proximity. Initial experimental results demonstrate that the DSXAI diagnostic system performs well, successfully reconstructing 2-dimensional (2D) tomographic SXR emissivity and T_e on the HL-2A tokamak. This study provides valuable insights for the future implementation of similar diagnostic systems on fusion reactors like ITER.