1111.4024 (Thiem Hoang et al.)

Revisiting Acceleration of Charged Grains in Magnetohydrodynamic Turbulence    [PDF]

Thiem Hoang, A. Lazarian, R. Schlickeiser

We study the acceleration of charged grains by magnetohydrodynamics (MHD) turbulence in the interstellar medium (ISM). We begin with revisiting gyroresonance acceleration by taking into account fluctuations of the grain guiding center along a uniform magnetic field (i.e. non-linear theory, NLT). We calculate grain velocity due to gyroresonance acceleration by fast modes using the NLT for different phases of the ISM, and compare with results obtained using quasi-linear theory (QLT). We find that the fluctuations of the grain guiding center reduce the grain velocity by less than 15 percent, but large grains are still accelerated to super-Alfvenic speed. For such super-Alfvenic grains, we investigate the effect of transit time damping (TTD) by fast modes. We find that due to the broadening of resonance condition in the NLT, the TTD acceleration is not only important for the cosine pitch angle $\mu>V_{A}/v$, but also for $\muView original: http://arxiv.org/abs/1111.4024