Study on the heat flux reconstruction with the infrared thermography for the divertor target plates in the KSTAR tokamak

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.

Design and implementation of plasma electron density measurements based on FPGA with all-phase FFT for tokamak devices

Plasma electron density is one of the most fundamental parameters when studying tokamak plasma physics, which is widely used in plasma control systems and plasma physics analyses. A hydrogen cyanide laser interferometer is generally applied to measure the plasma electron density in many tokamak devices. Therein, the plasma electron density is calculated by measuring the phase difference between the reference signal and the detector signal. This work provides a new way to realize real-time measurements of the plasma electron density with a phase comparator and processing system based on a field-programmable gate array chip. The system integrates a signal processing module, an all-phase fast Fourier transform (ap-FFT) module realized via matrix operations and phase comparisons, and a network communication module all in one board. This work concludes that the ap-FFT is robust and accurate for phase calculations compared with a windowing FFT. A data-reuse method and a phase shift method are proposed to improve the time resolution and phase range. The phase error is less than 0.1° and the time resolution is 0.025 ms, which is better than hardware methods and traditional software methods. This system is highly flexible with reduced design costs to meet the requirements of a tokamak, which can provide a valuable reference for other tokamak and phase difference comparisons.

Error estimations of the heat flux reconstruction for ITER divertor infrared thermography

This study developed a new heat flux reconstruction code based on the dual reciprocity boundary element method for the International Thermonuclear Experimental Reactor (ITER) divertor infrared (IR) thermography system. To use divertor heat flux reconstruction in ITER, we modeled the boundary condition between the coolant pipe inner wall and the coolant based on the temperature-dependent heat transfer coefficient and also considered the temperature dependence of tungsten thermal properties. Using this reconstruction code, we evaluated the sensitivity of the input data errors, divertor coolant temperature, and surface temperature errors on the accuracy of heat flux reconstruction by using simplified heat flux profiles, which are spatially uniform on the top surface of the monoblocks. This heat flux reconstruction method demonstrated that highly accurate heat flux reconstruction can be achieved for high heat flux cases in ITER; however, further studies are needed for low heat flux reconstruction.