Initial plasma achieved within engineering constraints in the PLATO tokamak

Abstract

In order to save flux consumption and lessen engineering requirements, the achievable toroidal loop voltage tends to be lowered in modern tokamaks. In such devices, careful optimization of the plasma startup scenario is often required to achieve a successful tokamak discharge. The PLATO tokamak, which is recently built at Kyushu University, also faces challenges in the plasma startup. PLATO employs an air-cored central solenoid that limits the loop voltage and creates stray magnetic fields. In addition, only simple capacitor banks with modest maximum charging voltages are available for the generation of the poloidal magnetic and toroidal electric fields in the initial operation. To realize the breakdown and plasma current ramp-up under those constraints, the configuration of coils and capacitor bank settings has been optimized to produce sufficient loop voltage while minimizing the stray field inside the vacuum chamber at the onset of the discharge. Through this optimization, a tokamak discharge with a plasma current of 30 kA and a pulse duration of 20 ms has been achieved.