Observation of a Relaxed Plasma State in a Quasi-Infinite Cylinder

Gray, T.; Brown, M. R.; Dandurand, D.

doi:10.1103/physrevlett.110.085002

Cited by 29 publications

(68 citation statements)

References 18 publications

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“…The solar wind is highly variable but there are two broad types: fast wind (V > 600 km/s) which is emitted from open coronal field lines and is typically low density (<5 protons/cm 3 ), has few large scale structures and has high amplitude but less developed turbulence, and slow wind, (V < 500 km/s) which is typically found in the ecliptic plane and originates from more complex coronal magnetic topology and is denser and more structured than the fast wind with more evolved but lower amplitude turbulence [26,27]. Here we use multiday long intervals of a fast wind stream (January [14][15][16][17][18][19][20][21]2008) and a slow wind stream (January [24][25][26][27][28][29]2010) with large scale magnetic fluctuations on the order of 10 nT.…”

Section: Introductionmentioning

confidence: 99%

“…The MHD wind tunnel configuration of the Swarthmore Spheromak Experiment (SSX) consists of a plasma gun which injects a spheromak of magnetized plasma into an ∼1-m-long cylindrical copper flux conserver [17]. Probes embedded in the chamber collect data on turbulent fluctuations inḂ as the plasma evolves down the length of the tube, eventually relaxing into a Taylor state [17][18][19][20]. After injection the plasma is completely dynamical, as there is no guide or vacuum field in the body of the chamber.…”

Section: Introductionmentioning

confidence: 99%

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Permutation entropy and statistical complexity analysis of turbulence in laboratory plasmas and the solar wind

et al. 2015

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. 2015. Permutation entropy and statistical complexity analysis of turbulence in laboratory plasmas and the solar wind. Phys. Rev. E 91, 023101.PHYSICAL REVIEW E 91, 023101 (2015) Permutation entropy and statistical complexity analysis of turbulence in laboratory plasmas and the solar wind The Bandt-Pompe permutation entropy and the Jensen-Shannon statistical complexity are used to analyze fluctuating time series of three different turbulent plasmas: the magnetohydrodynamic (MHD) turbulence in the plasma wind tunnel of the Swarthmore Spheromak Experiment (SSX), drift-wave turbulence of ion saturation current fluctuations in the edge of the Large Plasma Device (LAPD), and fully developed turbulent magnetic fluctuations of the solar wind taken from the Wind spacecraft. The entropy and complexity values are presented as coordinates on the CH plane for comparison among the different plasma environments and other fluctuation models. The solar wind is found to have the highest permutation entropy and lowest statistical complexity of the three data sets analyzed. Both laboratory data sets have larger values of statistical complexity, suggesting that these systems have fewer degrees of freedom in their fluctuations, with SSX magnetic fluctuations having slightly less complexity than the LAPD edge I sat . The CH plane coordinates are compared to the shape and distribution of a spectral decomposition of the wave forms. These results suggest that fully developed turbulence (solar wind) occupies the lower-right region of the CH plane, and that other plasma systems considered to be turbulent have less permutation entropy and more statistical complexity. This paper presents use of this statistical analysis tool on solar wind plasma, as well as on an MHD turbulent experimental plasma.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Permutation entropy and statistical complexity analysis of turbulence in laboratory plasmas and the solar wind

et al. 2015

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“…Since the magnetic helicity of a plasma is reflective of the twistedness or knottedness of the magnetic fields, a scan of magnetic helicity can be used to vary the magnetic field structure and potentially modify the character of current sheets in the plasma. A novel experiment developed on the MHD wind-tunnel configuration of the Swarthmore Spheromak Experiment (SSX) [16,17] explores this possible relationship between the observed intermittency in magnetic fluctuations and the magnetic helicity of the plasma. Given the nature of the plasma source on the SSX, a magnetic helicity injection can be very finely controlled, and thus resulting changes in turbulent characteristics-including both spectra and intermittency-can be carefully examined.…”

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Observation of Turbulent Intermittency Scaling with Magnetic Helicity in an MHD Plasma Wind Tunnel

2014

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“…For equilibria with a magnetic X-point, the location of the X-point must also be specified. The flexibility and simplicity of these solutions make them useful for verifying the accuracy of numerical solvers and for theoretical studies of Taylor states in laboratory experiments.Plasmas in both astrophysical and laboratory settings have a strong tendency to relax to minimum energy states known as Taylor states or Woltjer-Taylor states [1][2][3][4][5][6][7][8][9][10][11][12] in which the magnetic fields are force-free fields given by the equationwhere λ is a global constant. A well-known analytic solution to equation (1) is often used for theoretical studies and to interpret experiments [5][6][7]13 .…”

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confidence: 99%

“…Plasmas in both astrophysical and laboratory settings have a strong tendency to relax to minimum energy states known as Taylor states or Woltjer-Taylor states [1][2][3][4][5][6][7][8][9][10][11][12] in which the magnetic fields are force-free fields given by the equation…”

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Exact axisymmetric Taylor states for shaped plasmas

Cerfon

O’Neil

2014

Physics of Plasmas

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We present a general construction for exact analytic Taylor states in axisymmetric toroidal geometries. In this construction, the Taylor equilibria are fully determined by specifying the aspect ratio, elongation, and triangularity of the desired plasma geometry. For equilibria with a magnetic X-point, the location of the X-point must also be specified. The flexibility and simplicity of these solutions make them useful for verifying the accuracy of numerical solvers and for theoretical studies of Taylor states in laboratory experiments.Plasmas in both astrophysical and laboratory settings have a strong tendency to relax to minimum energy states known as Taylor states or Woltjer-Taylor states [1][2][3][4][5][6][7][8][9][10][11][12] in which the magnetic fields are force-free fields given by the equationwhere λ is a global constant. A well-known analytic solution to equation (1) is often used for theoretical studies and to interpret experiments [5][6][7]13 . One of its main advantage is its simplicity, but it lacks the degrees of freedom necessary to describe the large variety of configurations observed in laboratory experiments. We present a new family of exact solutions to equation (1) and a general construction for the solutions that address this need. The new solutions, while still simple, have the flexibility to describe configurations within a wide range of aspect ratios, elongations, and triangularities. The plasma boundary can have a magnetic separatrix, if desired, and the location of the separatrix can be specified. The equilibria we describe in this article can thus be useful for a variety of applications, including the study of non-solenoidal current start-up in low aspect ratio toroidal devices 10 and plasma dynamics in spheromaks. They can also be used to verify the accuracy of numerical schemes developed to solve equation (1) in fusionrelevant geometries 14,15 . Efficient solvers for force-free magnetic fields have recently become particularly attractive as a building block in a promising formulation for three-dimensional equilibria in fusion devices 16,17 . The exact solutions we present in this article can in that sense be thought of as the equivalent of Solov'ev solutions used to benchmark Grad-Shafranov solvers which are designed to compute more general equilibria 18 . The ability to construct exact equilibria with magnetic X-points is very desirable, since X-points are usually a source of difficulty in both theoretical studies and in numerical solvers. Our construction of analytic solutions works as follows. We first turn equation (1) into its associated GradShafranov equation for the poloidal flux function ψ. We a) Electronic mail: cerfon@cims.nyu.edu b) Electronic mail: oneil@cims.nyu.edu then express the solution ψ as a finite sum of functions satisfying the Grad-Shafranov equation. Finally, in order to have the ψ contours conform with shaped plasmas relevant to laboratory experiments, we determine the free constants appearing in the finite sum of functions such that the edge of the plasma, g...

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Observation of a Relaxed Plasma State in a Quasi-Infinite Cylinder

Cited by 29 publications

References 18 publications

Permutation entropy and statistical complexity analysis of turbulence in laboratory plasmas and the solar wind

Permutation entropy and statistical complexity analysis of turbulence in laboratory plasmas and the solar wind

Observation of Turbulent Intermittency Scaling with Magnetic Helicity in an MHD Plasma Wind Tunnel

Exact axisymmetric Taylor states for shaped plasmas

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