Conceptual design of a poloidal field coil system and operation scenario for an inductively operated day-long pulsed tokamak reactor

The conceptual design of a poloidal field coil system and operation scenario for an inductively operated day-long pulsed tokamak (IDLT) reactor are discussed. Much attention is paid to the start-up and shut-down phase, because a shorter dwell time is preferable in the pulsed reactor. A plasma current ramp-up time of 100 s is achievable with a power supply of 1.4 GW. Including the current ramp-down time and recharging periods, it is found that a dwell time of 5-10 min is feasible for IDLT reactor operation. The average hysteresis loss of the central solenoid coil is about 5 kW during the current ramp-up phase, and is acceptable for the superconducting coils. Plasma performance is analyzed with a 1.5-dimensional transport code, where a Bohm type transport model is employed. It is found that ignition can be initiated with an auxiliary heating power of 40 MW with the H factor of approximately 2, and can be sustained for a helium recycling coefficient less than R_He = 0.99. For IDLT reference operation with R_He = 0.95 and peaking parameter C_v = 1.0, it is found that the helium accumulation fraction is 9.8%, the ratio of helium effective particle confinement time τ_p* to energy confinement time τ_E is 7.8, and the bootstrap current fraction is 40%. During the shut-down phase, the decrease in plasma density is slower than the decrease in fusion power, and an auxiliary heating power of 20 MW is required to avoid density-limit disruption.