HR: 0800h
AN: SH31A-1154    [Abstracts]
TI: Non-Resonant Pitch-Angle Scattering of Sub-MeV Electrons
AU: * Ragot, B R
EM: heliores@yahoo.com
AF: Helio Research, P.O. Box 1414, Nashua, NH 03061 United States
AB: As the translational energy of charged particles decreases, so does the wavelength of the waves with which these particles can gyroresonate. For sub-MeV electrons, the resonant processes of wave-particle interaction involve waves that contain only a small fraction of the turbulent wave energy, even for small pitch-angles. It is very uncertain whether these resonant processes can dominate the scattering in pitch-angle. We therefore estimate the contribution of that part of the turbulence spectrum that contains most of the turbulent wave energy, but interacts with the electrons by a non-resonant process. The study of such non-resonant interaction has been restricted so far to very small pitch-angle cosines $\mu$ and higher energies. We now calculate the effect of the non-resonant waves at larger $\mu$. We find that the non-resonant interaction of sub-MeV electrons with low-frequency waves produces an anomalous scattering. The electron pitch-angle sines can subdiffuse or supradiffuse in logarithmic space as a function of the elapsed distance along the average magnetic field. In the solar wind, subdiffusion seems to be the rule. The average pitch-angle variation due to non-resonant interaction on lengthscales of the order of a fraction of the electron travel distance from the Sun is found to be comparable to the initial pitch-angle of the electrons, and much larger than the pitch-angle reduction due to magnetic focusing in slow solar wind. Therefore, unless the electrons are injected along the magnetic field and do not encounter any enhanced whistler turbulence, or the fast mode component of the turbulence is much lower than the measured compressive component of the turbulence, already only a few percent of the whole turbulence, sub-MeV electrons in the inner heliosphere do not propagate scatter free. A simulation of the electron dynamics based on the direct integration of the equations of motion, involving some $10^{15}$ modes, confirms these results. Electrons with small initial pitch-angles keep small pitch-angles. On the other hand, electrons with large initial pitch-angles have much larger pitch-angle variations, and within a finite range from 90 degrees, can be reflected very quickly. So, while the non-resonant scattering process is consistent with the first electrons arriving at one AU being strongly beamed along the magnetic field in some solar events, it also offers the possibility of significant scattering and delay of the electrons before their beaming.
DE: 7514 Energetic particles (2114)
DE: 7843 Numerical simulation studies
DE: 7859 Transport processes
DE: 7867 Wave/particle interactions
DE: 2118 Energetic particles, solar
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2004 AGU Fall Meeting