The feasibility of a tokamak reactor with a very high aspect ratio plasma

Feasibility of a very high aspect ratio tokamak reactor is investigated. He re, the aspect ratio A is the ratio of plasma major radius R, to the minor radius a,,. Over a wide range of A (= 2.7 similar to 8), the plasma size, c urrent drive power P-CD, divertor heat load W-DIV are calculated for the st eady-state plasma when the fusion power P-FUS (=3 GW) and the maximum toroi dal field B-TMAX (= 18 T) are fixed. Here, the inboard shield thickness del ta (TF) = 1.4 m, the normalized beta beta (N) = 3, plasma elongation kappa = 1.4, plasma temperature T = 15 keV and other parameters are similar to th ose of ITER. It is clarified that the acceptable current-drive power (P-CD = 81 MW), large fusion gain (Q = 37) and small divertor heat load (W-DIV si milar to 10 MW m(-2)) are achieved in a very high-A plasma with R-P/a(P)= 1 2/1.5 m. Radial build is optimized with keeping the field ripple ratio cons tant. When the number of TF-coil ( = 20) and ripple level ( = 1%) are fixed , the inboard shield thickness delta (TF) is increased by 0.8 m and outboar d shield thickness by 1.4 m as A increases from 2.7 to 8. In this case, the internal diameter of TF-coil increases by about 0.4 m since the plasma min or radius a, is decreased by 0.9 In. In the future power plant using SIC st ructural material, the very high-ii reactor is greatly superior to the low- A reactor since the large shielding region is available without degrading p lasma performance. These results are dependent on the plasma elongation kap pa and normalized beta beta (N). When kappa is increased from 1.4 to 1.7, t he required B-TMAX is reduced from 18 to 15 T. If an advanced operation (be ta (N) similar to 5) with reversed shear plasma is available, the required B-TMAX is reduced from 18 to 14.5 T. (C) 2000 Published by Elsevier Science S.A. All rights reserved.