A theoretical framework for low-frequency electromagnetic (drift-)kinetic turbulence in a collisionless, multi-species plasma is presented. The result generalises reduced magnetohydrodynamics (RMHD) and kinetic RMHD (Schekochihin et al. 2009) for pre
ssure-anisotropic plasmas, allowing for species drifts---a situation routinely encountered in the solar wind and presumably ubiquitous in hot dilute astrophysical plasmas (e.g. intracluster medium). Two main objectives are achieved. First, in a non-Maxwellian plasma, the relationships between fluctuating fields (e.g., the Alfven ratio) are order-unity modified compared to the more commonly considered Maxwellian case, and so a quantitative theory is developed to support quantitative measurements now possible in the solar wind. The main physical feature of low-frequency plasma turbulence survives the generalisation to non-Maxwellian distributions: Alfvenic and compressive fluctuations are energetically decoupled, with the latter passively advected by the former; the Alfvenic cascade is fluid, satisfying RMHD equations (with the Alfven speed modified by pressure anisotropy and species drifts), whereas the compressive cascade is kinetic and subject to collisionless damping. Secondly, the organising principle of this turbulence is elucidated in the form of a generalised kinetic free-energy invariant. It is shown that non-Maxwellian features in the distribution function reduce the rate of phase mixing and the efficacy of magnetic stresses; these changes influence the partitioning of free energy amongst the various cascade channels. As the firehose or mirror instability thresholds are approached, the dynamics of the plasma are modified so as to reduce the energetic cost of bending magnetic-field lines or of compressing/rarefying them. Finally, it is shown that this theory can be derived as a long-wavelength limit of non-Maxwellian slab gyrokinetics.
A Hybrid Physical-Chemical Vapour Deposition (HPCVD) system consisting of separately controlled Mg-source heater and substrate heater is used to grow MgB2 thin films and thick films at various temperatures. We are able to grow superconducting MgB2 th
in films at temperatures as low as 350 C with a Tc0 of 35.5 K. MgB2 films up to 4 um in thickness grown at 550 C have Jc over 10E6 A/cm2 at 5 K and zero applied field. The low deposition temperature of MgB2 films is desirable for all-MgB2 tunnel junctions and MgB2 thick films are important for applications in coated conductors.
We present zero-field {mu}SR measurements for LiY$_{1-x}$Ho$_{x}$F$_{4}$ samples with x = 0.0017, 0.0085, 0.0406, and 0.0855. We characterize the dynamics associated with the formation of the (F-{mu}-F)$^{-1}$ complex by comparing our data to Monte C
arlo simulations to determine the concentration range over which the spin dynamics are determined primarily by the Ho$^{3+}$-{mu} interaction rather than the F-{mu} interaction. Simulations show that F-{mu}-F oscillations should evolve into a Lorentzian Kubo-Toyabe decay for an increasing static magnetic field distribution {Gamma} (i.e., increasing x), but the data do not show this behavior, consistent with the recently reported existence of strong magnetic fluctuations in this system at low temperatures. Anisotropy in the field distribution is shown to cause small errors of order 10% from behavior predicted for an isotropic distribution. Finally, numerical calculations show that values of {Gamma} calculated in the single ion limit greatly exceed the values extracted from curve fits, suggesting that strong correlations play an important role in this system.
We investigate the anisotropy of Alfvenic turbulence in the inertial range of slow solar wind and in both driven and decaying reduced magnetohydrodynamic simulations. A direct comparison is made by measuring the anisotropic second-order structure fun
ctions in both data sets. In the solar wind, the perpendicular spectral index of the magnetic field is close to -5/3. In the forced simulation, it is close to -5/3 for the velocity and -3/2 for the magnetic field. In the decaying simulation, it is -5/3 for both fields. The spectral index becomes steeper at small angles to the local magnetic field direction in all cases. We also show that when using the global rather than local mean field, the anisotropic scaling of the simulations cannot always be properly measured.
