Improvement of infrared imaging video bolometer for application to deuterium experiment on the large helical device

Deposited layer substrate (DeLaS)-A module for radiation measurement

Infrared Imaging Video Bolometer (IRVB) measures the radiation from plasma in two-dimensions. IRVB uses a few micrometer thick metal foil as a radiation absorber. The foil being ultra-thin has several limitations. A new radiation absorbing module is proposed here that can effectively overcome the shortcomings of the foils used in IRVB. This module is developed by depositing carbon and metal thin films on an infrared transmitting substrate using magnetron sputtering. This patented module is termed Deposited Layer on a Substrate. A prototype is developed and laboratory tests are carried out using a laser source to demonstrate its feasibility as a radiation detector. The advantages of this module over conventional foils, its development, and experimental results validating the concept are discussed in this article.

Sensitivity improvement of infrared imaging video bolometer for divertor plasma measurement

The sensitivity of an infrared imaging video bolometer (IRVB) was improved for the measurement of relatively low energy plasma radiation from the viewpoint of the metal foil absorber material. The photon energy of the radiation was considered up to 1 keV for the divertor plasma measurement. The thickness of the foil absorber was evaluated not only for conventional heavy elements, e.g., platinum, but also for light elements by the relation between the photon energy and attenuation length and by mechanical strength. A heat-transfer calculation using ANSYS suggested that light elements with practical foil thickness provide a higher temperature rise of the foil absorber compared with heavier elements with practical foil thickness. The maximum of the temperature rise was evaluated using He-Ne laser irradiation onto absorber samples. The material dependence of the temperature rise has a similar tendency between calculations and experiments. Experimentally, the sensitivity of the IRVB improved from 280 to 110 µW/cm² using titanium with 1 µm thickness compared with conventional platinum with 2.5 µm thickness. Consequently, the signal-to-noise ratio of the IRVB could be improved from 2.8 to 9.1.