Extensive calculations of trapping rates of passing ions in thermal barriers of tandem mirrors have been performed with the aid of a square-well Fokker-Planck code. Consideration of the form of the kinetic equation and boundary conditions shows that the trapping rate depends on the ratios of barrier potential depth to passing ion temperature, Zeϕ/T, mirror magnetic field to barrier field, R, and total barrier density to passing density, g. A scaling formula is presented which fits the results over a wide range of = Zeϕ/T,R and g. In the limit of low the trapping frequency scales as R5/4/(g−l)5/3, and as R2/5/(g−1)2at large .
ICRF produced thermal barriers in a three-cell axisymmetric tandem mirror