Presentation Optimization of Magnetic Sensor Configuration for JT-60SA Plasma Control

武智, 学

JT-60SA, which has fully super conducting coils, is designed and now being constructed for the sake of supplement ITER toward DEMO after about eighteen-years JT-60U operation. In order to obtain information for control of JT-60SA plasma and physics research on the plasma, many types of magnetic sensors are developed. Reconstruction of plasma last closed flux surface (LCFS) and position is most basic and important for the plasma operation and the assessment of a plasma performance. For JT-60SA, they will be reproduced with magnetic sensors by the method of Cauchy condition surface (CCS) as an inverse problem in real time. CCS method uses the magnetic field signals from magnetic probes and magnetic flux signals from flux loops for the Dirichlet and Neumann conditions, respectively, in addition to the poloidal coil current. Recently, precise CCS reconstruction method, which was developed by tuning the position and size of the CCS surface, achieved error less than one centimeter at LCFS and divertor strike point. In order to determine the minimum number and adequate position of magnetic probes and flux loops, we access the accuracy of reconstruction by CCS method with various numbers of them. The reconstruction was performed from start to end of the plasma discharge with plasma current from 0.2MA to 5.5MA. Requirement for reconstruction accuracy is set to be the error less than 1 cm at diverter hit point and LCFS not to contact with the wall. The simulation was performed with and without the noise of the magnetic sensor observed in JT-60U and estimated eddy current on the vacuum vessel (VV) and stabilizing plate (SP). The minimum number of magnetic probe is decided as seventeen on VV and six on SP. In fact, seventeen probes will be used for CCS calculation. The minimum number of flux loop is decided as eighteen on VV and six on SP. Actually, nineteen loops will be used. However, we will install as many number of flux loop as possible because the replacement after the construction of tokamak is difficult.
The joint meeting of the 26th International Toki Conference (ITC-26) and The 11th Asia Plasma and Fusion Association Conference

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