Inadequacies of finite Larmor radius treatments of the internal tilting instability in field-reversed configurations

Abstract

A finite Larmor radius treatment of the tilting instability for field-reversed configurations is presented. It is shown on two accounts that such a treatment is inappropriate. First, the finite Larmor radius terms become infinite at the field null of the magnetic axis, because of the breakdown of the small Larmor radius assumption. Second, numerical computations using realistic parameters show that the magnetic moments of the ions are very poorly conserved at the tips of the flux surfaces in field-reversed configuration equilibria. Therefore finite Larmor radius theories cannot be used reliably to explain the observed stability to tilting of field-reversed configuration experiments.