Comparison of the Au and Ta foil parameters from laser calibration of imaging bolometer foils

Parchamy, H.*; Peterson, B. J.*; Hayashi, Hiromi*; Konoshima, Shigeru; Ashikawa, Naoko*; Seo, D. C.*; Kawashima, Hisato; JT-60 Team

The calibration technique of the imaging bolometer foil gives confidence in the measured values of the plasma radiation power. In this work, we improve the accuracy of the calibration by using a new IR camera (60 Hz, 320 240 pixels, 7.5-13 microns) in a calibration laboratory (low noise environment) with a close-up lens which provides a spatial resolution of 0.09 mm which is nearly 7 times better than the previous in situ calibration using a different IR camera. Tantalum, Ta, is offered for improved sensitivity, foil strength, and lower neutron cross-section compared to the previously used gold foil. In this paper we report, the local foil properties (the thermal diffusivity, the thermal conductivity, and the thickness) of a single graphite-coated gold foil (a nominal thickness of 2.5 microns) compared with those of a single graphite-coated tantalum foil (a nominal thickness of 5 microns) for an imaging bolometer through calibration with a He-Ne laser.