Calibration and thermal test results of prototype bolometer sensors for ITER fusion reactor

Abstract

For over 10 years, several bolometer sensors with different properties have been tested in the IBOVAC facility. The aim has been to develop a bolometer sensor that can be operated in ITER and can withstand harsh operating conditions. For this purpose, important physical properties of the sensors, i.e., cooling time constant τ, normalized heat capacity κ, and normalized sensitivity s n, have been characterized in a vacuum condition and at various temperatures up to 300 °C. The calibration is achieved by ohmic heating of the sensor absorbers by applying a DC voltage and recording exponential current fall during heating. Recently, a Python program was developed to analyze the data and extract the above mentioned parameters including the uncertainties from recorded currents. In the present series of experiments, the latest prototype sensors developed for ITER are tested and evaluated. These include three different sensor types: two with Au absorbers on ZrO2 membranes (self-supporting substrate sensors) and one with Au absorbers on Si3N4 membranes supported by a Si frame (supported membrane sensors). Tests revealed that the sensor with ZrO2 substrate can only be operated up to 150 °C, while the supported membrane sensors passed the tests up to 300 °C successfully. These results will be used, together with other upcoming tests, such as irradiation testing, to select the most suitable sensors to be employed in ITER.

Optimizing ITER Bolometer Cameras in View of Internal Reflections and Crosstalk Between Channels

“…To determine the minimum number of internal apertures that can suppress crosstalk of light between channels inside a collimator, a simple optimization procedure has been developed. With the locations of the sensors being defined by their placement inside ITER to achieve the desired LOS as well as the geometry of sensor prototypes [9], the relative position and size of apertures in the TopPlate (see Fig. 1) are determined In the case of simulated geometry four evenly spaced internal apertures fully suppress crosstalk.…”

“…For example, stray radiation from the electron-cyclotron heating system can be minimized by design [6], and geometric uncertainties by design measures, metrology, and optical characterization [7], [8]. Additional sources of uncertainty and errors have been characterized, such as calibration factors (with an error of the order of 1%) [9], pressure effects [10], and correction for temperature dependence of calibration factors [11]. Compensation for other sources of uncertainty is still to be demonstrated, such as cable length and reflections on the first wall inside the vacuum vessel (in other diagnostics in the visible and UV range the reflections are a significant concern [12]).…”

Progress of the bolometer diagnostic system on EAST

“…The metal foil resistive bolometer and the AXUV detector are extensively used for radiated power measurements in present fusion devices, such as DIII-D [3], LHD [4], ASDEX-Upgrade (AUG) [5], and others. Both detector types are deployed in the bolometer diagnostic systems on EAST [6].…”