Modeling Nuclear Fusion with an Ultracold Nonneutral Plasma

Abstract

In the hot dense interiors of stars and giant planets, nuclear fusion reactions are predicted to occur at rates that are greatly enhanced compared to those at low densities. The enhancement is caused by plasma screening of the repulsive Coulomb potential between nuclei, which increases the probability of the rare close collisions that are responsible for fusion. This screening enhancement is a small effect in the Sun, but is predicted to be much larger in dense objects such as white dwarf stars and giant planet interiors where the plasma is strongly correlated (i.e. where the Debye screening length is smaller than a mean interparticle spacing). However, strongly enhanced fusion reaction rates caused by plasma screening have never been definitively observed in the laboratory. This talk discusses a method for observing the enhancement using an analogy between nuclear energy and cyclotron energy in a cold nonneutral plasma in a strong magnetic field. In such a plasma, the cyclotron frequency is higher than other dynamical frequencies, so the kinetic energy of cyclotron motion is an adiabatic invariant. This energy is not shared with other degrees of freedom except through rare close collisions that break this invariant and couple the cyclotron motion to the other degrees of freedom. Thus, the cyclotron energy of an ion, like nuclear energy, can be considered to be an internal degree of freedom that is released only via rare close collisions. Furthermore, it has recently been shown that the rate of release of cyclotron energy is enhanced through plasma screening by precisely the same factor as that for the release of nuclear energy, because both processes rely on close collisions that are enhanced by plasma screening in the same way. Simulations and experiments measuring large plasma screening enhancements for the first time will be discussed, and the possibility of exciting and studying cyclotron burn fronts will also be considered.