The plasma and machine parameters of a pulsed tokamak reactor with a day-long operation period have been, 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, plasmas 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 = 10m, minor radius a = 1.85, plasma elongation K = 1.8, plasma current Ip = 12.2MA, toroidal field on axis Bt = 7.56 T, and safety factor at the plasma surface q↓ = 3. A plasma volume V approx. 1200m3 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 (approx. 15 MW) with a heating time of only a few tens of seconds is sufficient to achieve the ignition condition. This is well within the capacity of auxiliary heating systems currently used in large tokamak devices. A confinement improvement factor (from L mode) of fL > 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 〈T〉 = 20 keV with a toroidal beta βt = 2.6% (Troyon factor g = 3), which gives a fusion power Pfus = 2.5 GW even for an alpha-particle dilution nα/ne 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. If the maximum toroidal field is set much higher, as in proposed recent reactor designs for the Steady-State Tokamak Reactor (SSTR) and ARIES, a more attractive plasma with a larger safety factor can be designed, and the pulse length can be extended remarkably.
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