Colorimetry in Nuclear Fusion Research

Colorimetry is a unique technique among research fields. The technique is also utilized in nuclear fusion research. The motivation is to evaluate the wide range of distribution of the deposition layer on the surface of the vacuum vessel. The deposition layer affects the control of fuel particles. Therefore, the result from colorimetry can contribute to the study of particle control in fusion plasma. In a particle control study, global particle balance analysis is usually conducted. Also, long-term samples irradiated by plasma have been analyzed. Colorimetry has the role of a bridge between these analyses. In this chapter, a demonstration of colorimetry in fusion devices is introduced.

Explainable Deep Learning for the Analysis of MHD Spectrograms in Nuclear Fusion

In the nuclear fusion community, there are many specialized techniques to analyze the data coming from a variety of diagnostics. One of such techniques is the use of spectrograms to analyze the magnetohydrodynamic (MHD) behavior of fusion plasmas. Physicists look at the spectrogram to identify the oscillation modes of the plasma, and to study instabilities that may lead to plasma disruptions. One of the major causes of disruptions occurs when an oscillation mode interacts with the wall, stops rotating, and becomes a locked mode. In this work, we use deep learning to predict the occurrence of locked modes from MHD spectrograms. In particular, we use a Convolutional Neural Network (CNN) with Class Activation Mapping (CAM) to pinpoint the exact behavior that the model thinks is responsible for the locked mode. Surprisingly, we find that, in general, the model explanation agrees quite well with the physical interpretation of the behavior observed in the spectrogram.

Technological Processes for Steel Applications in Nuclear Fusion

Plasma facing components for energy conversion in future nuclear fusion reactors require a broad variety of different fabrication processes. We present, along a series of studies, the general effects and the mutual impact of these processes on the properties of the EUROFER97 steel. We also consider robust fabrication routes, which fit the demands for industrial environments. This includes heat treatment, fusion welding, machining, and solid-state bonding. Introducing and following a new design strategy, we apply the results to the fabrication of a first-wall mock-up, using the same production steps and processes as for real components. Finally, we perform high heat flux tests in the Helium Loop Karlsruhe, applying a few hundred short pulses, in which the maximum operating temperature of 550 °C for EUROFER97 is finally exceeded by 100 K. Microstructure analyses do not reveal critical defects or recognizable damage. A distinct ferrite zone at the EUROFER/ODS steel interface is detected. The main conclusions are that future breeding blankets can be successfully fabricated by available industrial processes. The use of ODS steel could make a decisive difference in the performance of breeding blankets, and the first wall should be completely fabricated from ODS steel or plated by an ODS carbon steel.

Predicting the onset of nucleate boiling heat flux of one-side heated flat heat sink in sub-cooled flow conditions for fusion divertor cooling

For the cooling system of the future, nuclear fusion tokamak, to operate stably and continuously, it is important to identify potential hazards that may occur in the system in advance. Among the various potential hazards associated with the nuclear fusion tokamak, the onset of nucleate boiling (ONB) is a point at which the heat-transfer mechanism changes dramatically and is a crucial factor that must be addressed. In particular, the equipment inside the tokamak is loaded with a heat flux of several MW/m2 under single-side heating conditions, and it is important to predict the ONB under these special heating conditions. Therefore, in this study, the ONB of a flat heat sink was experimentally investigated under highly subcooled flow conditions. Based on the physical understanding of the thermo-hydraulic aspect of the ONB, the wall temperature gradient change point, which is mainly used in the subcooled flow condition, was selected as the ONB detection criterion. Trends in the ONB heat flux change were analyzed as representative system parameters that can be tuned in the cooling system, such as subcooling, mass flow rate, and pressure. In addition, the ONB correlations developed in the previous studies were evaluated for predicting the performance under one-side high heat load conditions. However, the large difference in the experimental conditions (range of system parameters and heating conditions) and the fact that the influence of system parameters was not reflected in the correlation resulted in high error rates. Therefore, the ONB correlation that can be used in the tokamak heat flux condition was newly developed through a dimensional analysis that can effectively reflect the influences in the correlation through dimensionless numbers. The developed correlation can be of great help in designing a diverter or blanket cooling system and establishing an operational strategy.