Prediction of high-beta disruptions in JT-60U based on sparse modeling using exhaustive search

• Published in: Fusion engineering and design 2019-03, Vol.140, p.67-80
• Main Authors: Yokoyama, T., Miyoshi, Y., Hiwatari, R., Isayama, A., Matsunaga, G., Oyama, N., Igarashi, Y., Okada, M., Ogawa, Y.
• Format: Article
• Language: English
• Subjects: Data-driven science; Disruption; Disruption prediction; Elongation; Inductance; JT-60U; Machine learning; Mathematical models; Modelling; Parameter identification; Performance enhancement; Performance prediction; Plasma; Plasma density; Sparse modeling; Support vector machines; Tokamak; Tokamak devices
• ISSN: 0920-3796; 1873-7196
• DOI: 10.1016/j.fusengdes.2019.01.128

•Disruption predictor based on high-beta plasma experimental data in JT-60U.•Input plasma parameters are selected by sparse modeling using exhaustive search.•Performance of prediction is improved by extracting input parameters.•Key parameters including magnetic fluctuation and its time delivered are extracted.•False alarm rate is improved considering temporal change of parameters. Disruption is a critical phenomenon in a tokamak reactor. Although disruption causes serious damage to the reactor, its physical mechanism remains unclear. To realize a tokamak reactor, it is necessary to understand and control the disruption phenomenon. The present research constructs a disruption predictor using experimental high-beta plasma data in the JT-60U tokamak. The predictor was constructed using a support vector machine as a linear discriminant, and we focus on a variable selection problem for the binary classification by sparse modeling, specifically, exhaustively searching the best combinations of variables which maximize the predictor performance. By the sparse modeling, we found that the six input parameters as the best combinations. The selected parameters were the n = 1 mode amplitude |Brn=1| and its time derivative d|Brn=1|/dt, the plasma density (relative to the Greenwald density limit) and its time derivative, and the time derivatives of the plasma internal inductance and plasma elongation. In particular, it was identified that the parameter d|Brn=1|/dt, plays a key role on plasma disruption. We should notice that the combination with other plasma parameters is indispensable and remarkably make it possible to improve the performance of disruption prediction.