Metal Resistor Bolometer Research Articles

Irradiation tests of bolometer sensor prototypes for ITER

In ITER, the bolometer diagnostic is foreseen to provide the measurements for the total plasma radiation. Sensors need to withstand the harsh environmental conditions. Most prominent among those is the nuclear environment with neutron fluxes up to 1013ncm2s at the locations of bolometers, which result in a radiation dose of up to 0.3dpa in Si3N4. Original metal resistor bolometer sensors based on Au-absorbers on a mica substrate with Au-meanders failed when exposed to fast neutron fluences corresponding to 0.1 dpa. Various material tests under irradiation identified ceramic materials like Al2O3, AlN or Si3N4 together with Pt meanders as promising alternatives. Based on these ideas a development campaign was initiated to produce a radiation hard bolometer sensor. Two approaches resulted in good mechanical stability under thermal cycling: Au absorbers supported by a Si3N4 membrane and Au absorbers on a silicon base plate which is hung up by flexure hinges. In order to assess their resistance against irradiation, tests have been conducted in the Budapest Neutron Centre. The test campaign demonstrated for the first time that bolometer sensors can withstand irradiation doses corresponding up to 0.3 dpa in Si3N4, which is higher than the value of 0.1 dpa requested by ITER project requirements, while their meander resistance measured after irradiation increased only by 20–30 Ω.

Error handling method for digital twin-based plasma radiation detection

Abstract In Industry 4.0 several new methods have been introduced to approximate the real and digital world. Digital twins represent real object together with their data and functions in the digital world. The latest developments in digital twin researches extend the application of following areas like simulation-based system engineering, simulation-based optimization and simulation-based control. Application of digital twin in plasma radiation detection gives a new opportunity to model the procedure of detection and discover the possible errors. This paper proposes a fuzzy based mathematical model of metal absorber–metal resistor bolometer as a digital twin. The use of a fuzzy logic based approach is herewith proposed and implemented, where fuzzy membership functions are assigned to different physical and geometrical properties of the metal resistor → metal absorber → camera housing → numerical assumptions back-calculation chain. Our fuzzy based digital twin is tested on results of numerical plasma simulations the uncertainties (as a possible sources of detection error) of which are also handled via fuzzy logic. The resulted mathematical model (camera + plasma) is a suitable tool to be able to estimate the overall error and uncertainty of radiation detection.

Bolometer developments in diagnostics for magnetic confinement fusion

The plasma radiation is an essential part of the power balance in current and future magnetic confinement fusion experiments and gives crucial insight for the challenges of power exhaust and divertor detachment as well as valuable information to understand plasma instabilities and transport effects. It is typically measured using various types of bolometers. Present day experimental devices, both the tokamak and stellarator, make use of metal resistor bolometers and infrared imaging video bolometers (IRVB), depending on the main focus of the respective measurement. The well-established sensor for absolutely calibrated measurements is the metal resistor bolometer. AXUV diodes, often used in conjunction with bolometers, are ideal for observing fast transient events in a plasma due to their very short response times, but their sensitivity varies significantly over the full radiation spectrum and degrades over their lifetime. In cases where many lines-of-sight are needed to observe radiation profiles in complex geometries IRVB offers the ability to integrate high channel counts in rather narrow installation volumes. Fibre-optic bolometers are a new development promising measurements immune to electro-magnetic interference. These diagnostic concepts are presented as well as their pros and cons. For future devices like ITER and DEMO, R&D efforts are required to adapt sensors and diagnostic schemes to the harsh nuclear environment. An overview will be given over the activities for sensor development and integration challenges, which may also be relevant for long pulse operation in present experiments.

Optimization of a bolometer detector for ITER based on Pt absorber on SiN membrane

Any plasma diagnostic in ITER must be able to operate at temperatures in excess of 200 °C and neutron loads corresponding to 0.1 dpa over its lifetime. To achieve this aim for the bolometer diagnostic, a miniaturized metal resistor bolometer detector based on Pt absorbers galvanically deposited on SiN membranes is being developed. The first two generations of detectors featured up to 4.5 μm thick absorbers. Results from laboratory tests are presented characterizing the dependence of their calibration constants under thermal loads up to 450 °C. Several detectors have been tested in ASDEX Upgrade providing reliable data but also pointing out the need for further optimization. A laser trimming procedure has been implemented to reduce the mismatch in meander resistances below 1% for one detector and the thermal drifts from this mismatch.

Design of a bolometer for Hanbit magnetic mirror device

We designed and constructed a metal-resistor bolometer to measure the total radiation of the plasma in the Hanbit device, a magnetic mirror machine at the Korea Basic Science Institute. The target parameters for the plasma, the duration of which was 100–500 ms, at the central cell were the ion energy of 1 keV, the electron temperature of 200 eV, and the electron density of 5×1012 cm−3. A preliminary test showed that the cooling time constant and the absolute sensitivity of the homemade bolometer were 12 ms and 0.031 V/mW, respectively; the sensitivity was calibrated using an Ar ion laser. A test run of the homemade bolometer in the Hanbit device produced a signal of ∼25 mW/cm2, which was equivalent to the total power loss of about 40 kW, for the input rf power of 200 kW.

Fast bolometric diagnostic in the RFX reversed field pinch experiment

Bolometric measurements are performed in the RFX reversed field pinch experiment by means of a low noise miniaturized multichannel metal resistor bolometer module. The first tests on RFX, an experiment with geometrical dimensions comparable with those of large tokamaks but characterized by a much faster plasma dynamics, show that this thin film bolometer can be operated with high bandwidth and high time resolution in very different fusion experiments. A new data analysis technique, which allows the derivation of the power absorbed by the bolometer at a high time resolution (Δt=3×10−5 s) for the study of fast phenomena is presented.

A low noise highly integrated bolometer array for absolute measurement of VUV and soft x radiation

A new low noise miniaturized multichannel bolometer module for absolute measurements in the VUV and soft x spectral ranges is described. Highly integrated four-channel modules (2×3.3×1.5 cm3) each comprising four independent ac-excited (50 kHz) metal resistor bolometer bridges were successfully tested on a large tokamak (Tore Supra in Cadarache) and on an electron synchrotron (BESSY in Berlin). The bolometer system features a linear response to the absorbed radiation power, a low detection limit (≤1.0×10−6 W cm−2 on Tore Supra with an integration time of τint=10×10−3 s) and a low NEP (≤10×10−9 W on BESSY). The thermal cross-talk between adjacent detectors is negligible (<0.003) and a low thermal drift ΔUBr/ΔT < 10−4 V °C−1 is achieved. It can be operated at a maximum temperature of 150 °C, at high magnetic fields (tested up to B=4.5 T in the laboratory) and survives high nuclear radiation doses. The system offers the possibility of detecting low-power VUV and soft x-radiation with sampling rates of up to 10 kHz on plasma machines and of absolutely calibrating VUV and soft x instruments. Effective suppression of electric, thermal and nuclear radiation interferences is characteristic of the bolometer system.Strain gauge effects, which could affect the behavior of the bolometers at high magnetic fields, are suppressed by the ac-excitation technique.

Bolometric diagnostics in JET

Radiation losses from the JET plasma are measured (temporally and spatially resolved) with three pin-hole cameras which observe one poloidal plasma cross section from underneath (one vertical camera with 14 bolometers) and from the side (two horizontal cameras with 10 bolometers each). In addition, eight collimated single bolometers monitor toroidal symmetry of plasma emissivity. An improved metal resistor bolometer capable of surviving at least 5000 D–T pulses in JET is composed of two identical foils (4-μm-thick gold absorber, 7.5-μm-thick Kapton substrate, and 0.1-μm-thick gold resistor), mounted one behind another in one housing. The rear foil serves as a reference bolometer in a bridge circuit. With an integration time constant of 20 ms a detection limit of 70 μW/cm2 was measured in JET. Examples of measuring results in JET are presented: strong poloidal asymmetries of the radiation density as precursor signals of a density limit disruption and the formation of a poloidally symmetric, cold plasma mantle before a disruption.

A new metal resistor bolometer for measuring vacuum ultraviolet and soft x radiation

A new metal resistor bolometer has been developed by applying thin-film technology. It is composed of three layers, a 4-μm-thick radiation absorber made of gold, a 7.5-μm-thick kapton dielectric, and a 0.1-μm-thick 5-kΩ gold resistor. This detector with the appropriate electronics shows a linear response to radiation power, including both neutral-particle emission and electromagnetic radiation from the soft x-ray part of the spectrum to the infrared. The bolometer has a very high operating reliability and sufficient suppression of ambient interference under extreme environmental conditions, such as high neutron and gamma radiation fluxes, high temperatures, mechanical vibrations, and strong electromagnetic fields. In plasma discharges in the ASDEX tokamak a radiation detection limit of 100 μW/cm2 was obtained at a time resolution of 10 ms. The bolometers of an array can be calibrated in situ; the calibration data are reproducible and stable in time within ±10%. Measurements in ASDEX which demonstrate the capability of the method are discussed.