An Alternating Current Tokamak Reactor with Ohmic Ignition and Bootstrap Current

An alternating current (ac) tokamak reactor with ohmic ignition and long pulses due to bootstrap current is proposed as a simple and quasi-continuous fusion power plant. An ohmic plasma current of 23 MA with a high toroidal field of ∼10 T in the Alternating Current Tokamak Reactor-Upgrade (ACTR-U) (10-m major radius and 2-m minor radius) provides the ohmic ignition. After entering the ignition regime, the plasma current is reduced by one-half to enhance the bootstrap current with a high-beta poloidal field (β_p ∼ 2) to prolong the pulse length. When the ohmic transformer reaches the maximum flux, the plasma current is ramped down and reversed; ac operation follows. We thus demonstrate that an ohmic transformer alone is in principle sufficient for a quasi-continuous deuterium-tritium fusion reactor.