Ohmic ignition of tokamak plasma via ultra-low-q discharge combined with adiabatic compression.

Abstract

Combination of ultra-low-q discharge with adiabatic compression expands the parametric window of Ohmic ignition significantly. The device of this scheme is, in essence, compact. Ohmic heating is enhanced by adiabatic compression because of further intensification of high current density which is specific to the ultra-low-q discharge. Typical example of device and plasma parameters with compression ratio 5 and safety factor 0.5 is as follows; major radius/minor radius=2 m/0.5 m, energy confinement time required for Ohmic ignition is less than 0.2 s, plasma current density is 50 MA/m2, and the total plasma current is 1.6 MA. Without compression longer energy confinement time and larger total plasma current are necessary. Free expansion of the current channel and/or increase of toroidal field induces the transition of ultra-low-q discharge to tokamak.