Parameter Optimization of the Inductively Operated Day-Long Tokamak Reactor

Abstract

The plasma and machine parameters of a pulsed tokamak reactor with a day-long operation period have been studied, where engineering constraints such as maximum toroidal field strength are preserved at International Thermonuclear Experimental Reactor (ITER) levels so as to realize a fusion reactor with only a short-range extension of currently available technology. To provide the magnetic flux necessary to sustain a plasma current inductively for 1 day or longer, plasma with a major radius of R > 9.5 m are necessary, and a plasma with an aspect ratio as high as A>5 should be employed. Typical parameters are as follows: major radius R = 10 m, minor radius a = 1.85 m, plasma elongation [kappa] = 1.8, plasma current I[sub p] = 12.2 MA, toroidal field on axis B[sub t] = 7.56 T, and safety factor at the plasma surface q[psi] = 3. A plasma volume V [approximately] 1200 m[sup 3] is comparable with that of ITER, even though the major radius of a day-long operation reactor is relatively large. A very small amount of heating power ([approximately]15 MW) with a heating time of only a few tens of seconds is sufficient to achieve the ignition condition. This is wellmore » within the capacity of auxiliary heating systems currently used in large tokamak devices. A confinement improvement factor (from L mode) of [line integral][sub L] > 1.7 is required to design a reactor with a reasonable machine size and a day-long pulse duration. The operation temperature is chosen to be [r angle]T[l angle] = 20 keV with a toroidal beta [beta][sub t] = 2.6% (Troyon factor g = 3), which gives a fusion power P[sub fus] = 2.5 GW even for an alpha-particle dilution n[sub [alpha]]/n[sub e] of 10%. The bootstrap current fraction is 50% or more of the total current, and current profile needed for the beta limit could be achieved with a combination of ohmic current in the plasma center region and bootstrap current in the outer region. 23 refs., 8 figs., 2 tabs.« less