The surface eroding thermocouple for fast heat flux measurement in DIII-D

Application of two-dimensional temperature response functions for reconstruction of divertor heat flux profile in commercial fusion reactors

To keep the tritium breeding rate TBR > 1 and to meet the high heat load and neutron shielding requirements for the first wall and divertor in fusion demonstration (DEMO) reactors, the number of port plugs and other openings must be limited. To accomplish this, it is necessary to develop alternatives to the use of infrared (IR) thermography to determine the peak heat flux and the heat flux profile onto divertor targets. A divertor tile equipped with multiple temperature monitoring channels can be used to reproduce the temperature profile. To avoid the high temperatures and high neutron flux environment in a DEMO, the monitoring positions can be set well away from the irradiated surface. However, the spatial resolution of this method is lower than that provided by IR thermography. In the present work, we apply two-dimensional temperature response functions and the corresponding heat conduction model to temperature data obtained from a divertor tile surface in the large helical device to study the effects of the spatial resolution of the monitored temperature profile on the reconstructed heat flux profile. The findings provide information that will be useful in defining a method for embedding thermocouples into the divertor tiles of future DEMO reactors.

Measurements of multiple heat flux components at the divertor target by using surface eroding thermocouples (invited)

The Surface Eroding Thermocouple (SETC) is a robust diagnostic utilized in DIII-D to provide fast, edge-localized modes (ELMs) resolved heat flux measurements, in particular in geometric regions that are too shadowed for traditional infrared thermography. In order to further investigate the power dissipation in the divertor region, a combination of flush-mounted and recessed SETCs was developed to assess the effect on surface heating from non-charged particles at the divertor target. Utilizing the Divertor Materials Evaluation System sample exposure platform, the first demonstration of the feasibility of using this new method to distinguish between the heat flux from charged particles and that from neutrals and radiative heating was achieved. This paper details the process of using the combination of flush SETCs and recessed SETCs to measure the multiple heat flux components at the divertor target and further discusses how to determine two important ratios, α (ratio of heat flux from charged particles deposit on recessed SETC to that deposit on flush SETC) and β (ratio of heat flux from non-charged particles deposit on recessed SETC to that deposit on flush SETC), in the estimation of the heat flux from non-charged particle sources. Using a time dependent ratio α, it was found that ∼50% of the total incident heat flux is attributable to the non-charged particles in the fully detached open divertor in DIII-D. Finally, the new application of similar SETC diagnostics in the Small Angle Slot divertor with a V-like configuration and partial tungsten coated surface (SAS-VW) is also introduced.

Study on the characteristics of thermo-electrodes of various deposition parameters for the flexible temperature sensor

In the paper, the flexible temperature sensor based on polyimide is designed and fabricated by magnetron sputtering technology. The impact of vacuum degree, sputtering power, and argon flow rate on the roughness and deposition rate of two thermo-electrodes [indium tin oxide (ITO)/indium oxide (In₂O₃)] is investigated with orthogonal experiment. The thermoelectric properties of the sensor are greatly improved by low temperature heat treatment. The sensitivity of the ITO film and In₂O₃ film increases by 2.61 times and 2.89 times, respectively, after 1 h low-temperature heat treatment. According to the comprehensive evaluation, an innovative step annealing process is proposed to optimize the heat treatment of the prepared thermo-electrodes. The fabricated flexible thin film thermocouples exhibit great operating characteristics in the low temperature measurement range. When the hot end's temperature reaches 181.5 °C, the thermoelectric force can reach 7.84 mV and the average Seebeck coefficient can reach 50.55 µV/°C. The repeatability and hysteresis error of the sensor is ±0.88% and 1.90%, respectively. The sensor in this work shows great application potential for in situ real-time temperature measurement in robotic dexterous hands, electronic skin, and foldable devices.

Effect of Annealing on the Thermoelectricity Properties of the WRe26-In2O3 Thin Film Thermocouples

WRe26-In₂O₃ (WRe26 (tungsten-26% rhenium) and In₂O₃ thermoelectric materials) thin film thermocouples (TFTCs) have been fabricated based on magnetron sputtering technology, which can be used in temperature measurement. Many annealing processes were studied to promote the sensitivity of WRe26-In₂O₃ TFTCs. The optimal annealing process of the thermocouple under this kind of RF magnetron sputtering method was proposed after analyzing the properties of In₂O₃ films and the thermoelectric voltage of TFTCs at different annealing processes. The calibration results showed that the WRe26-In₂O₃ TFTCs achieved a thermoelectric voltage of 123.6 mV at a temperature difference of 612.9 K, with a sensitivity of up to 201.6 µV/K. Also, TFTC kept a stable thermoelectric voltage output at 973 K for 20 min and at 773 K for two hours. In general, the WRe26-In₂O₃ TFTCs developed in this work have great potential for practical applications. In future work, we will focus on the thermoelectric stability of TFTCs at higher temperatures.

WRe26-In2O3 probe-type thin film thermocouples applied to high temperature measurement

A novel probe-type thin film thermocouple has been fabricated successfully for high temperature measurement applications. WRe26 (tungsten-26% rhenium)-In₂O₃ thermoelectric materials were used in the thermocouples to achieve high thermoelectric output and high temperature resistance. The films were deposited on a cylindrical substrate by magnetron sputtering technology. The annealing process of the thermocouples was studied to achieve optimal performance. The calibration results showed the thermoelectric output of WRe26-In₂O₃ thin film thermocouples reached 93.7 mv at 700 °C, and its sensitivity was 165.5 µV/°C under the temperature of the cold junction, which was 133.8 °C. The thermocouples developed in this work have great potential for practical applications.