Increased accuracy and signal-to-noise ratio through recent improvements in infra-red video bolometer fabrication and calibration.

The infra-red video bolometer (IRVB) is a diagnostic equipped with an infra-red camera that measures the total radiated power in thousands of lines of sight within a large field of view. Recently validated in MAST-U [Fderici et al., Rev.

Data streaming infra-red video bolometer (IRVB) of Korea Superconducting Tokamak Advanced Research (KSTAR).

Due to the increasing demands for active plasma control operations, in situ diagnostics are highly sought after. Tungsten plasma-facing components have been utilized in the Korea Superconducting Tokamak Advanced Research (KSTAR) lower divertor since the 2023 campaign. Plasma radiation is a key parameter for plasma control, especially in radiation front control experiments.

Consideration of signal to noise ratio for an imaging bolometer for ITER.

An infrared imaging video bolometer (IRVB) is proposed for ITER having a tangential view of the entire ITER cross section. For the initial estimate of the signal level, a 840 m plasma is assumed to uniformly radiate 67.3 MW.

Reconstruction of radiation profiles near the plasma boundary using an infrared imaging video bolometer in KSTAR.

An infrared imaging video bolometer using tomographic inversion can provide the total radiated power and 2-D radiation profiles, which are crucial information for impurity seeding experiments. Because large amounts of impurities exist at the plasma edge, accurate reconstruction of the radiation profiles near the material boundary is an important issue. In this study, two methods of boundary condition treatment are compared.

Forward projection matrix derivation through Monte-Carlo ray-tracing of KSTAR infra-red imaging video bolometer (IRVB).

The infrared imaging video bolometer (IRVB) as a foil bolometry technique can be an alternative solution to the conventional resistive bolometer due to its electro-magnetic immunity and 2D plasma profiles. The plasma profile of the IRVB cannot be directly derived from the foil images due to the difference between the foil pixel number and the plasma pixel number and the line integrated nature of the incident rays on the foil. So, it needs tomography such as the Phillips-Thikhonov algorithm.

Signal to noise ratio of upgraded imaging bolometer for KSTAR.

An InfraRed imaging Video Bolometer (IRVB) was installed on KSTAR in 2012 having a ∼2 m × 7 cm × 9 cm Pt foil blackened with graphite and a 5 mm × 5 mm aperture located 7.65 cm from the foil with 16 × 12 channels and a time resolution of 10 ms. The IR camera was an Indigo Phoenix (InSb, 320 × 256 pixels, 435 fps, <25 mK).

Development of bolometric tomography technique for high-contrast radiation distribution in toroidal devices.

An extended Computed Tomography (CT) technique with a priori information based on Phillips-Tikhonov regularization has been developed to handle a high-contrast radiation distribution, which can result in large reconstruction errors in the region where radiation intensity is low, with few line of sight (LOS) data. Reference profiles generated from LOS data for every time slice are employed as the a priori information. In the extended technique, the weighting parameter for the reference profile is automatically determined from the LOS data, to avoid an inappropriate reference.

Conceptual design of imaging bolometer for use of computed tomography in JT-60SA.

An InfraRed imaging Video Bolometer (IRVB) system in JT-60SA has been designed for the two-dimensional (2D) Computed Tomography (CT) analysis of radiation. To achieve complete viewing of the whole poloidal cross section for plasmas having a low aspect ratio, a new IRVB concept, which has two sets of pin-hole camera systems viewing two different directions, has been introduced. Fields of view of the IRVB have been successfully designed by moving apertures to be sufficient for CT use without installation in tangential ports.

Using a priori knowledge for developing bolometric tomography in toroidal devices.

In tomographic imaging of magnetically confined toroidal plasmas, a countermeasure against missing observation has been studied in terms of the adoption of prior information based on modelled plasma profiles. The Tikhonov regularization for image reconstruction is extended by the use of the Euclidean distance. A procedure of model fitting is designed in order to adaptively generate the reference image.

Three-dimensional tomographic imaging for dynamic radiation behavior study using infrared imaging video bolometers in large helical device plasma.

A three-dimensional (3D) tomography system using four InfraRed imaging Video Bolometers (IRVBs) has been designed with a helical periodicity assumption for the purpose of plasma radiation measurement in the large helical device. For the spatial inversion of large sized arrays, the system has been numerically and experimentally examined using the Tikhonov regularization with the criterion of minimum generalized cross validation, which is the standard solver of inverse problems. The 3D transport code EMC3-EIRENE for impurity behavior and related radiation has been used to produce phantoms for numerical tests, and the relative calibration of the IRVB images has been carried out with a simple function model of the decaying plasma in a radiation collapse.

A reconsideration of the noise equivalent power and the data analysis procedure for the infrared imaging video bolometers.

The infrared imaging video bolometer (IRVB) used for measurement of the two-dimensional (2D) radiation profiles from the Large Helical Device has been significantly upgraded recently to improve its signal to noise ratio, sensitivity, and calibration, which ultimately provides quantitative measurements of the radiation from the plasma. The reliability of the quantified data needs to be established by various checks. The noise estimates also need to be revised and more realistic values need to be established.

Improved signal to noise ratio and sensitivity of an infrared imaging video bolometer on large helical device by using an infrared periscope.

An Infrared imaging Video Bolometer (IRVB) diagnostic is currently being used in the Large Helical Device (LHD) for studying the localization of radiation structures near the magnetic island and helical divertor X-points during plasma detachment and for 3D tomography. This research demands high signal to noise ratio (SNR) and sensitivity to improve the temporal resolution for studying the evolution of radiation structures during plasma detachment and a wide IRVB field of view (FoV) for tomography. Introduction of an infrared periscope allows achievement of a higher SNR and higher sensitivity, which in turn, permits a twofold improvement in the temporal resolution of the diagnostic.

Calibration of a thin metal foil for infrared imaging video bolometer to estimate the spatial variation of thermal diffusivity using a photo-thermal technique.

A thin metal foil is used as a broad band radiation absorber for the InfraRed imaging Video Bolometer (IRVB), which is a vital diagnostic for studying three-dimensional radiation structures from high temperature plasmas in the Large Helical Device. The two-dimensional (2D) heat diffusion equation of the foil needs to be solved numerically to estimate the radiation falling on the foil through a pinhole geometry. The thermal, physical, and optical properties of the metal foil are among the inputs to the code besides the spatiotemporal variation of temperature, for reliable estimation of the exhaust power from the plasma illuminating the foil.

Development of imaging bolometers for magnetic fusion reactors (invited).

Imaging bolometers utilize an infrared (IR) video camera to measure the change in temperature of a thin foil exposed to the plasma radiation, thereby avoiding the risks of conventional resistive bolometers related to electric cabling and vacuum feedthroughs in a reactor environment. A prototype of the IR imaging video bolometer (IRVB) has been installed and operated on the JT-60U tokamak demonstrating its applicability to a reactor environment and its ability to provide two-dimensional measurements of the radiation emissivity in a poloidal cross section. In this paper we review this development and present the first results of an upgraded version of this IRVB on JT-60U.