Gyrofluid description of Alfvenic turbulence and its parallel electric field

Abstract: Anisotropic Alfv\'{e}nic fluctuations with $k_{\parallel}/k_{\perp}\ll 1$ remain at frequencies much smaller than the ion cyclotron frequency in the presence of a strong background magnetic field. Based on the simplest truncation of the electromagnetic gyrofluid equations in a homogeneous plasma, a model for the energy cascade produced by Alfv\'{e}nic turbulence is constructed, which smoothly connect the large magnetohydrodynamics (MHD) scales and the small "kinetic" scales. Scaling relations are obtained for the electromagnetic fluctuations, as a function of $k_{\perp}$ and $k_{\parallel}$. Moreover, a particular attention is paid to the spectral structure of the parallel electric field which is produced by Alfv\'{e}nic turbulence. The reason is the potential implication of this parallel electric field in turbulent acceleration and transport of particles. For electromagnetic turbulence, this issue was raised some time ago in [A. Hasegawa, K. Mima, J. Geophys. Res. {\bf 83} 1117 (1978)].