Dynamic Phase Alignment In Inertial Alfven Turbulence

In weakly collisional plasma environments with sufficiently low electron beta, Alfvenic turbulence transforms into inertial Alfvenic turbulence at scales below the electron skin depth, k(perpendicular to)d(e) greater than or similar to 1. We argue that, in inertial Alfvenic turbulence, both energy and generalized kinetic helicity exhibit direct cascades. We demonstrate that the two cascades are compatible due to the existence of a strong scale dependence of the phase alignment angle between velocity and magnetic field fluctuations, with the phase alignment angle scaling as cos alpha(k) proportional to k(perpendicular to)(-1). The kinetic and magnetic energy spectra scale as proportional to k(perpendicular to)(-5/3) and proportional to k(perpendicular to)(-11/3), respectively. As a result of the dual direct cascade, the generalized helicity spectrum scales as proportional to k(perpendicular to)(5/3), implying progressive balancing of the turbulence as the cascade proceeds to smaller scales in the k(perpendicular to)d(e) >> 1 range. Turbulent eddies exhibit a phase-space anisotropy k parallel to proportional to k(perpendicular to)(5/3), consistent with critically balanced inertial Alfven fluctuations. Our results may be applicable to a variety of geophysical, space, and astrophysical environments, including the Earth's magnetosheath and ionosphere, solar corona, and nonrelativistic pair plasmas, as well as to strongly rotating nonionized fluids.