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(EX/P3-18) Scaling and Modeling Studies of High-Bootstrap-Fraction Tokamaks

F.W. Perkins¹⁾, T.A. Casper²⁾, P.A. Politzer^3)
 
1) Princeton Plasma Physics Laboratory, Princeton, USA
²⁾ Lawrence Livermore National Laboratory, Livermore, California, USA
³⁾ General Atomics, San Diego, California, USA

Abstract.  A steady-state tokamak reactor will depend almost entirely on bootstrap current as a source for the poloidal magnetic field. Examination of a model for a tokamak with plasma current arising solely from the bootstrap current finds a steady-state solution to the coupled heat- and poloidal-flux-diffusion equations. The model uses a gyroBohm heat diffusivity that depends on the poloidal field, coupling heat diffusion and poloidal field diffusion physics. The problem is cast in terms of coupled, nondimensional ODEs and associated eigenvalues. Numerical solution of these equations yields a rather flat relative q-profile and a triangular temperature profile. The eigenvalues produce the scaling expressions T(0) = 1.2 ^. P^{0.667 .} (R/a)^0.33 and I_p = 0.23 ^. n^{0.5 .} P^0.33a [P:MW, T:keV, I_p:MA, a:m, n: 10¹⁹m^{- 3}]. Experimental plans call for DIII-D and C-Mod discharges heated by a source with no direct current drive capability. Extrapolation from DIII-D discharges indicates that $\beta_{p}^{}$ = 3 (required for unity bootstrap fraction) can be attained with MHD stability if I_p $\sim$ 0.6 MA. *Work supported by U.S. DOE Contracts DE-AC02-76CH03073, DE-AC03-99ER54463, W-7405-ENG-48.

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