Feasibility Analysis of 100 kA DC Commutation Scheme to be Applied in the Quench Protection Unit of CFETR

Abstract

China fusion engineering test reactor is a new tokamak device, which is one design option under the consideration of the China National Integration Design Group employs superconducting magnets. The main target of this project is to build a self-sufficient fusion engineering tokamak reactor with its fusion power 50-200 MW. Toroidal field coils, center solenoid coils, and poloidal field (PF) coils, whose rated current range from 52.9 to 90 kA, produce the magnetic field for plasma generation and confinement. The core of quench protection unit is to divert the coil current into discharge resistor by using commutation technology, which should be determined by the rated current and voltage requirement of magnets. Different kinds of technologies for quench protection unit (QPU) are considered, and an advanced commutation technology composed of a mechanical bypass switch, vacuum circuit breaker (VCB), and LC commutation circuit based on artificial current zero technology has been worked out to meet the current and voltage requirement (10 kV/100 kA). To provide a faster and more reliable removal of the energy stored in those superconducting coils, this paper analyzes in detail the feasibility of a commutation scheme based on artificial current zero technology by analyzing and simulating each stage of the commutation process at such large rated current and voltage conditions. Both analysis and simulation results verified that the operating reliability of QPU can be guaranteed by this 100 kA dc commutation scheme.