Circuit design for doubling the toroidal magnetic field on the QUEST spherical tokamak.

• Circuit design to double the toroidal magnetic field on the QUEST spherical tokamak is in progress. • Electron cyclotron (EC) resonances in QUEST changes with a high field. Fundamental resonance for 28 GHz EC waves emerges on the high field side. • The toroidal coil current to double the field is 100 kA. The current source consists of the 125 power supply modules in parallel. • A module comprises a bank of lithium-ion capacitors and a DC–DC buck converter. • In the bench test of a single module, the current increased linearly and maintained the flattop as programmed. Various scenarios of electron cyclotron heating can be explored in a spherical tokamak with a high toroidal field. On the QUEST spherical tokamak, doubling the toroidal field results in the emergence of the fundamental resonance layer for 28 GHz electron cyclotron waves. The second-harmonic resonance layer shifts toward the plasma central area. To increase the coil current from 50 to 100 kA, a current source is designed with 125 modules in parallel. The module power supply comprises a bank of lithium-ion capacitors and a DC–DC buck converter. In the bench test of a single module, the current was found to increase linearly and maintained the flat-top as programmed. [ABSTRACT FROM AUTHOR]