Nearly Periodic Maps and Geometric Integration of Noncanonical Hamiltonian Systems.

M. Kruskal showed that each continuous-time nearly periodic dynamical system admits a formal (1)-symmetry, generated by the so-called roto-rate. When the nearly periodic system is also Hamiltonian, Noether's theorem implies the existence of a corresponding adiabatic invariant.

Role of Kinetic Instability in Runaway-Electron Avalanches and Elevated Critical Electric Fields.

The effects of kinetic whistler wave instabilities on the runaway-electron (RE) avalanche is investigated. With parameters from experiments at the DIII-D National Fusion Facility, we show that RE scattering from excited whistler waves can explain several poorly understood experimental results. We find an enhancement of the RE avalanche for low density and high electric field, but for high density and low electric field the scattering can suppress the avalanche and raise the threshold electric field, bringing the present model much closer to observations.

Effective critical electric field for runaway-electron generation.

In this Letter we investigate factors that influence the effective critical electric field for runaway-electron generation in plasmas. We present numerical solutions of the kinetic equation and discuss the implications for the threshold electric field. We show that the effective electric field necessary for significant runaway-electron formation often is higher than previously calculated due to both (1) extremely strong dependence of primary generation on temperature and (2) synchrotron radiation losses.