Influence of collisions and incoherence on ion-cyclotron transport in mirror plasmas

The effects of classical Coulomb collisions and wave incoherency on drift-cyclotron-loss-cone (drift-cone) mode anomalous transport are studied analytically and by simulation. Pitch-angle collisions have a cumulative effect on the gyrophase angle, and the spatially varying magnetic field in a mirror well contributes a large geometrical amplification of the gyrophase-angle diffusion. Analytical calculations of this effect for particles with arbitrary pitch angle are confirmed by Monte Carlo simulations. However, for the levels of drift-cone turbulence observed in the 2XIIB magnetic mirror experiment and for its relative collisionality, the effect of pitch-angle collisions on anomalous transport is small. In particular, heating of ions to 40 keV energies cannot be explained by this mechanism. Wave incoherency also destroys superadiabaticity, leads to velocity transport, and provides an approximate model of the finite frequency bandwidth of drift-cone turbulence, e.g., due to bursting effects in 2XIIB. Monte Carlo simulations corroborate the analytical transport theory presented. The simulations exhibit significantly enhanced velocity-space transport and heating of ions to nearly 40 keV energies due to wave incoherency for parameters at the limit of applicability to the 2XIIB experiment. These same considerations of resonant wave-particle interactions are also directly relevant to electron and ion-cyclotron resonance heating and to velocity diffusion driven by unstable Alfven-ion-cyclotron waves in other mirror experiments