Comparison of the Au and Ta Foil Parameters from laser Calibration of Imaging Bolometer Foils

Abstract

The calibration technique of the imaging bolometer foil gives confidence in the measured values of the plasma radiation power. In this paper we improve the accuracy of the calibration of the imaging bolometer foil by using an IR camera (FLIR/SC500) (60 Hz, 320 x 240 pixels, 7.5-13 mum) in a calibration laboratory (low noise environment) with a close-up lens, which provides a spatial resolution of ~0.09 mm which is ~7 times better than the previous in situ calibration using a different IR camera (Indigo/Omega) (30 Hz, 160 x 120 pixels, 7.5-13.5 mum). In addition the foil material is changed for the development of the imaging bolometer. Tantalum (Ta) is offered for improved sensitivity, foil strength, and lower neutron cross-section compared to the previously used gold foil of the imaging bolometer for the JT-60U tokamak. In this paper we report the local foil properties (the thermal conductivity (constant), and the thickness) of a single graphite-coated gold foil (a nominal thickness of 2.5 mum) for LHD compared with those of a single graphite-coated tantalum foil (a nominal thickness of 5 mum) for JT-60U by calibration with a He-Ne laser.