  We argue that the Maxwellian approximation can essentially underestimate the
rates of some nuclear reactions in hot plasma under conditions very close to
thermal equilibrium. This phenomenon is demonstrated explicitly on the example
of reactions in self-sustained DT fusion plasma with admixture of light
elements X = Li, Be, C. A kinetic analysis shows that the reactivity
enhancement results from non-Maxwellian knock-on perturbations of ion
distributions caused by close collisions with energetic fusion products. It is
found that although the fraction of the knock-on ions is small, these particles
appreciably affect the D+X and T+X reaction rates. The phenomenon discussed is
likely to have general nature and can play role in other laboratory and
probably astrophysical plasma processes.
