79 results found
Kunz MW, Schekochihin AA, Chen CHK, et al., 2015, Inertial-range kinetic turbulence in pressure-anisotropic astrophysical plasmas, Journal of Plasma Physics, Vol: 81, ISSN: 1469-7807
A theoretical framework for low-frequency electromagnetic (drift-)kineticturbulence in a collisionless, multi-species plasma is presented. The resultgeneralises reduced magnetohydrodynamics (RMHD) and kinetic RMHD (Schekochihinet al. 2009) for pressure-anisotropic plasmas, allowing for species drifts---asituation routinely encountered in the solar wind and presumably ubiquitous inhot dilute astrophysical plasmas (e.g. intracluster medium). Two mainobjectives are achieved. First, in a non-Maxwellian plasma, the relationshipsbetween fluctuating fields (e.g., the Alfven ratio) are order-unity modifiedcompared to the more commonly considered Maxwellian case, and so a quantitativetheory is developed to support quantitative measurements now possible in thesolar wind. The main physical feature of low-frequency plasma turbulencesurvives the generalisation to non-Maxwellian distributions: Alfvenic andcompressive fluctuations are energetically decoupled, with the latter passivelyadvected by the former; the Alfvenic cascade is fluid, satisfying RMHDequations (with the Alfven speed modified by pressure anisotropy and speciesdrifts), whereas the compressive cascade is kinetic and subject tocollisionless damping. Secondly, the organising principle of this turbulence iselucidated in the form of a generalised kinetic free-energy invariant. It isshown that non-Maxwellian features in the distribution function reduce the rateof phase mixing and the efficacy of magnetic stresses; these changes influencethe partitioning of free energy amongst the various cascade channels. As thefirehose or mirror instability thresholds are approached, the dynamics of theplasma are modified so as to reduce the energetic cost of bendingmagnetic-field lines or of compressing/rarefying them. Finally, it is shownthat this theory can be derived as a long-wavelength limit of non-Maxwellianslab gyrokinetics.
Rincon F, Schekochihin AA, Cowley SC, 2015, Non-linear mirror instability, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 447, Pages: L45-L49, ISSN: 0035-8711
Wicks RT, Roberts DA, Mallet A, et al., 2014, CORRELATIONS AT LARGE SCALES AND THE ONSET OF TURBULENCE IN THE FAST SOLAR WIND (vol 778, pg 177, 2013), ASTROPHYSICAL JOURNAL, Vol: 782, ISSN: 0004-637X
Wicks RT, Roberts DA, Mallet A, et al., 2013, Correlations at Large Scales and the Onset of Turbulence in the Fast Solar Wind, The Astrophysical Journal, Vol: 778, Pages: 177-177, ISSN: 0004-637X
We show that the scaling of structure functions of magnetic and velocity fields in a mostly highly Alfvénic fast solar wind stream depends strongly on the joint distribution of the dimensionless measures of cross helicity and residual energy. Already at very low frequencies, fluctuations that are both more balanced (cross helicity ~0) and equipartitioned (residual energy ~0) have steep structure functions reminiscent of "turbulent" scalings usually associated with the inertial range. Fluctuations that are magnetically dominated (residual energy ~−1), and so have closely anti-aligned Elsasser-field vectors, or are imbalanced (cross helicity ~1), and so have closely aligned magnetic and velocity vectors, have wide "1/f" ranges typical of fast solar wind. We conclude that the strength of nonlinear interactions of individual fluctuations within a stream, diagnosed by the degree of correlation in direction and magnitude of magnetic and velocity fluctuations, determines the extent of the 1/f region observed, and thus the onset scale for the turbulent cascade.
Abel IG, Plunk GG, Wang E, et al., 2013, Multiscale gyrokinetics for rotating tokamak plasmas: fluctuations, transport and energy flows, REPORTS ON PROGRESS IN PHYSICS, Vol: 76, ISSN: 0034-4885
Meyer H, Abel IG, Akers RJ, et al., 2013, Overview of physics results from MAST towards ITER/DEMO and the MAST Upgrade, NUCLEAR FUSION, Vol: 53, ISSN: 0029-5515
Ghim Y-C, Schekochihin AA, Field AR, et al., 2013, Experimental Signatures of Critically Balanced Turbulence in MAST, PHYSICAL REVIEW LETTERS, Vol: 110, ISSN: 0031-9007
Wicks RT, Mallet A, Horbury TS, et al., 2013, Alignment and Scaling of Large-Scale Fluctuations in the Solar Wind, Physical Review Letters, Vol: 110, Pages: 025003-025003, ISSN: 0031-9007
Chen CHK, Mallet A, Schekochihin AA, et al., 2012, Three-Dimensional Structure of Solar Wind Turbulence, The Astrophysical Journal, Vol: 758, Pages: 120-120
We present a measurement of the scale-dependent, three-dimensional structureof the magnetic field fluctuations in inertial range solar wind turbulence withrespect to a local, physically motivated coordinate system. The Alfvenicfluctuations are three-dimensionally anisotropic, with the sense of thisanisotropy varying from large to small scales. At the outer scale, the magneticfield correlations are longest in the local fluctuation direction, consistentwith Alfven waves. At the proton gyroscale, they are longest along the localmean field direction and shortest in the direction perpendicular to the localmean field and the local field fluctuation. The compressive fluctuations arehighly elongated along the local mean field direction, although axiallysymmetric perpendicular to it. Their large anisotropy may explain why they arenot heavily damped in the solar wind.
Schekochihin AA, Highcock EG, Cowley SC, 2012, Subcritical fluctuations and suppression of turbulence in differentially rotating gyrokinetic plasmas, PLASMA PHYSICS AND CONTROLLED FUSION, Vol: 54, ISSN: 0741-3335
Vaivads A, Andersson G, Bale SD, et al., 2012, EIDOSCOPE: particle acceleration at plasma boundaries, EXPERIMENTAL ASTRONOMY, Vol: 33, Pages: 491-527, ISSN: 0922-6435
Heinemann T, McWilliams JC, Schekochihin AA, 2011, Large-Scale Magnetic Field Generation by Randomly Forced Shearing Waves, PHYSICAL REVIEW LETTERS, Vol: 107, ISSN: 0031-9007
Zocco A, Schekochihin AA, 2011, Reduced fluid-kinetic equations for low-frequency dynamics, magnetic reconnection, and electron heating in low-beta plasmas, PHYSICS OF PLASMAS, Vol: 18, ISSN: 1070-664X
Highcock EG, Barnes M, Parra FI, et al., 2011, Transport bifurcation induced by sheared toroidal flow in tokamak plasmas, PHYSICS OF PLASMAS, Vol: 18, ISSN: 1070-664X
Barnes M, Parra FI, Schekochihin AA, 2011, Critically Balanced Ion Temperature Gradient Turbulence in Fusion Plasmas, PHYSICAL REVIEW LETTERS, Vol: 107, ISSN: 0031-9007
Chen CHK, Mallet A, Yousef TA, et al., 2011, Anisotropy of Alfvénic Turbulence in the Solar Wind and Numerical Simulations, Monthly Notices of the Royal Astronomical Society, Vol: 415, Pages: 3219-3226, ISSN: 0035-8711
Howes GG, TenBarge JM, Dorland W, et al., 2011, Gyrokinetic Simulations of Solar Wind Turbulence from Ion to Electron Scales, PHYSICAL REVIEW LETTERS, Vol: 107, ISSN: 0031-9007
Nazarenko SV, Schekochihin AA, 2011, Critical balance in magnetohydrodynamic, rotating and stratified turbulence: towards a universal scaling conjecture, JOURNAL OF FLUID MECHANICS, Vol: 677, Pages: 134-153, ISSN: 0022-1120
Rosin MS, Schekochihin AA, Rincon F, et al., 2011, A non-linear theory of the parallel firehose and gyrothermal instabilities in a weakly collisional plasma, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 413, Pages: 7-38, ISSN: 0035-8711
Barnes M, Parra FI, Highcock EG, et al., 2011, Turbulent Transport in Tokamak Plasmas with Rotational Shear, PHYSICAL REVIEW LETTERS, Vol: 106, ISSN: 0031-9007
Parra FI, Barnes M, Highcock EG, et al., 2011, Momentum Injection in Tokamak Plasmas and Transitions to Reduced Transport, PHYSICAL REVIEW LETTERS, Vol: 106, ISSN: 0031-9007
Kunz MW, Schekochihin AA, Cowley SC, et al., 2011, A thermally stable heating mechanism for the intracluster medium: turbulence, magnetic fields and plasma instabilities, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 410, Pages: 2446-2457, ISSN: 0035-8711
Wicks RT, Horbury TS, Chen CHK, et al., 2011, Anisotropy of Imbalanced Alfvenic Turbulence in Fast Solar Wind, Physical Review Letters, Vol: 106, Pages: 045001-045001, ISSN: 0031-9007
Uzdensky DA, Loureiro NF, Schekochihin AA, 2010, Fast Magnetic Reconnection in the Plasmoid-Dominated Regime, PHYSICAL REVIEW LETTERS, Vol: 105, ISSN: 0031-9007
Highcock EG, Barnes M, Schekochihin AA, et al., 2010, Transport Bifurcation in a Rotating Tokamak Plasma, PHYSICAL REVIEW LETTERS, Vol: 105, ISSN: 0031-9007
Wicks RT, Horbury TS, Chen CHK, et al., 2010, Power and Spectral Index Anisotropy of the Entire Inertial Range of Turbulence in the Fast Solar Wind, Monthly Notices of the Royal Astronomical Society, Vol: 407, Pages: L31-L35, ISSN: 0035-8711
We measure the power and spectral index anisotropy of magnetic field fluctuations in fast solar wind turbulence from scales larger than the outer scale down to the ion gyroscale, thus covering the entire inertial range. We show that the power and spectral indices above the outer scale of turbulence are approximately isotropic. The turbulent cascade causes the power anisotropy at smaller scales manifested by anisotropic scalings of the spectrum: close to k−5/3 across and k−2 along the local magnetic field, consistent with a critically balanced Alfvénic turbulence. By using data at different radial distances from the Sun and calculating the radial dependence of the ratio of the outer scale to the ion gyroscale, we show that the width of the inertial range does not change with heliocentric distance. At the smallest scales of the inertial range, close to the ion gyroscale, we find an enhancement of power parallel to the magnetic field direction coincident with a decrease in the perpendicular power. This is most likely related to energy injection by ion kinetic modes such as the firehose instability and also marks the beginning of the kinetic range, sometimes called the dissipation range, of solar wind turbulence.
Chen CHK, Horbury TS, Schekochihin AA, et al., 2010, Anisotropy of Solar Wind Turbulence between Ion and Electron Scales, Physical Review Letters, Vol: 104, Pages: 255002-255002, ISSN: 0031-9007
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