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Bootstrap current in Tokamaks with neutral injection

For a diffuse pinch plasma in the near collisionless (“banana”) regime the fast ion current produced by injection of ≥ 10 A, 30 keV neutral hydrogen constitutes a sufficient seed current for the bootstrap effect. Assuming an effective ion charge number Z ∼ 2 due to impurities, the seed current density on the magnetic axis is calculated and incorporated into the steady-state moment equations describing the bootstrap equilibria of Bickerton et al. In the parameter space spanned by the seed current and the mass input, a practically accessible region exists where m = 1 (kink) and resistive modes may be avoided. With present technology the injection-driven bootstrap current may double the Ohmic current, but the concomitant mass input for injection parallel to the magnetic axis is too small to compensate for the neoclassical diffusion losses. The theory is applied to the ORMAK and PLT experiments.