Mini Tokamak for Diagnostic and Coil-Driver Testing

Jean Nelson^1*, Chun-Yi Chen², Jie-Ling Liou³, Keng-Yu Lin⁴, Yung-Wei Pi¹, Po-Yu Chang¹

¹Institute of Space and Plasma studies, National Cheng-Kung University, Tainan, Taiwan
²International Bachelor Degree Program on Energy Engineering, National Cheng-Kung University, Tainan, Taiwan
³Department of Photonics, National Cheng-Kung University, Tainan, Taiwan
⁴Department of Physics, National Cheng-Kung University, Tainan, Taiwan

* Presenter:Jean Nelson, email:jeannelson247@gmail.com

This work presents the development of a current driver capable of providing a pre-designed current profile for the Toroidal Field Coils (TFCs), the Central Solenoid (CS), and thte Poloidal Field Coils (PFCs), alongside the design and implementation of a mini-Tokamak. The mini-Tokamak, a tabletop setup, has been developed for two main purposes: (1) to test current drivers for achieving specific current profiles and (2) to evaluate diagnostic components such as the B-dot probe, flux tube, and Rogowski Coil. The goal of this device is to replicate conditions found in larger-scale systems within a compact form factor. For example, this setup will serve as a testing environment for components intended to be used in the Formosa Integrated Spherical Tokamak (FIRST), a spherical tokamak currently being designed in Taiwan. In addition, we are demonstrating the feasibility of using super-capacitors and Pulsed Width Modulation (PWM) combining the H-bridge modules to generate the required current profile for FIRST by testing the concept on the mini-Tokamak Additionally, this system serves as an interactive educational platform, offering hands-on experience for newcomers to the field. The setup features a cylindrical vacuum chamber with a diameter of 320 mm and a height of 500 mm with four TFCs. A spherical tokamak with a major radius of 85 mm and a minor radius of 55 mm will be generated using inductive breakdown with PFCs in the vacuum chamber. The planned toroidal field will reach up to ~0.2 T at 85mm when the TFCs are driven by a current of 20 kA. The generated field will be used to test the B-dot probed developed. Finally, we will show the results for the current profile up to 1.8kA (the rating of our IGBT module) for a single capacitor bank as well as tests involving parallelization of multiple capacitor banks for reaching higher currents will also be presented.

Keywords: Magnetic Confinemen Fusion, Plasma Physics, Tokamaks