The Dynamics of Dissipation Range Fluctuations with Application to Cosmic Ray Propagation Theory

Robert J.\ Leamon, Norman F.\ Ness and Charles W.\ Smith

Proceedings of the 26th International Cosmic Ray Conference, in press (1999)

Abstract:

Unlike larger spatial scales of the interplanetary magnetic field fluctuation spectrum, study of the smallest scale fluctuations (comparable to the gyroradius of a thermal proton) which form the so-called dissipation range has been somewhat neglected. This spectral range is characterized by a steeply falling power spectrum and frequently nonzero magnetic helicity, features thought to result from the dissipation of magnetic fluctuations by thermal particle populations. Although this range contains relatively little energy, it is relevant to energetic particle scattering because low-rigidity particles and all particles at large pitch angles become resonant with these fluctuations. Analyzing power and helicity spectra of WIND data, we deduce the orientation of the wavevectors and find that most of the wave energy is associated with wavevectors at large angles to the mean magnetic field. We place these observations within an existing framework for turbulent scattering of cosmic rays.