System development of Formosa Integrated Research Spherical Tokamak (FIRST), the first Tokamak in Taiwan

We are building a spherical Tokamak with a major and minor radius of 45 cm and 32 cm, respectively. In this work, we are focusing on developing the system of the spherical Tokamak, e.g., the current drivers that drive all coils, the calculation of the eddy current on the chamber wall induced by the time-varying current of the central solenoid, and the magnetic field using 3-axis B-dot probes, etc. For the current driver, supercapacitors with H-bridge configurations are used so that any current profiles can be provided. For the eddy current calculation, a simple circuit model, including the mutual inductance between coils and the chamber wall, is solved using the Preconditioned Conjugate Gradient (PCG) method. Therefore, the required loop voltage and, thus, the current profile of the central solenoid, including the eddy current, are calculated. For magnetic field measurement, 3-axis B-dot probes can provide all magnetic field components. Designs and the testing results will be presented.