Imazu (1986) claims that a magnetic field can halve the nuclear reaction rate in a high temperature plasma. In a comment Jarvis (1987) points out that this must be incorrect because a magnetic field has no effect on the velocity distribution of particles in thermodynamic equilibrium, and assigned the error to a misinterpretation of a geometrical model in equation (7). Jarvis' criticism can be further strengthened by considering the tensor expansion of the Fokker-Planck equation (Johnston, 1960). Here it is clear that the magnetic field only affects f1(giving the usual magnetic effects on current and heat flux) and higher order terms. Indeed Imazu specifically assumes that f is only f0=fm(a Maxwellian) and all fn=0, n>or=1. It follows that the fusion collision rate will be unaffected by the magnetic field. Imazu further claims that the Coulomb collision rate is not affected in the same way as fusion reactions because in this case a 90 degrees collision is the sum of many simultaneous glancing collisions. This is a correct result but for the wrong reason.
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