Spheromak Formation by Steady Inductive Helicity Injection

Jarboe, T. R.; Hamp, W. T.; Marklin, G.J.; Nelson, B. A.; O'Neill, R.G.; Redd, A. J.; Sieck, P.E.; Smith, Roger; Wrobel, J.S.

doi:10.1103/physrevlett.97.115003

Cited by 42 publications

(37 citation statements)

References 28 publications

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“…22 In addition, the HiFi code 23 was used to follow the dynamical evolution of the cohelicity merging process using the second order Bessel function ͑double͒ spheromak solution as the initial state. The final state shown in Fig.…”

Section: ͑3͒mentioning

confidence: 99%

Observation of a nonaxisymmetric magnetohydrodynamic self-organized state

et al. 2010

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A nonaxisymmetric stable magnetohydrodynamic ͑MHD͒ equilibrium within a prolate cylindrical conducting boundary has been produced experimentally at Swarthmore Spheromak Experiment ͑SSX͒ ͓M. R. Brown et al., Phys. Plasmas 6, 1717 ͑1999͔͒. It has m = 1 toroidal symmetry, helical distortion, and flat profile. Each of these observed characteristics are in agreement with the magnetically relaxed minimum magnetic energy Taylor state. The Taylor state is computed using the methods described by A. Bondeson et al. ͓Phys. Fluids 24, 1682 ͑1981͔͒ and by J. M. Finn et al. ͓Phys. Fluids 24, 1336 ͑1981͔͒ and is compared in detail to the measured internal magnetic structure. The lifetime of this nonaxisymmetric compact torus ͑CT͒ is comparable to or greater than that of the axisymmetric CTs produced at SSX; thus suggesting confinement is not degraded by its nonaxisymmetry. For both one-and two-spheromak initial state plasmas, this same equilibrium consistently emerges as the final state.

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Section: ͑3͒mentioning

confidence: 99%

Observation of a nonaxisymmetric magnetohydrodynamic self-organized state

et al. 2010

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“…It is of interest to note that a recent spheromak experiment has successfully produced such a mixed helical and axisymmetric relaxed state in the laboratory (Jarboe et al 2006). One of the earliest astrophysical applications of Taylor relaxation, which is on the knot structure of a jet, also invokes this geometrical dependence of the relaxed state (Königl & Choudhuri 1985).…”

Section: Geometric or Morphological Dependence Of Self-organized Statesmentioning

confidence: 99%

“…Also, a more powerful power supply, i.e., higher injector voltage, is likely to drive an that has a large peaking factor. One way to overcome this difficult is to do away with such material electrodes, which motivates the design of the HIT-SI experiment (Jarboe et al 2006). …”

Section: The Implication Of a Near Taylor Statementioning

confidence: 99%

Self‐Organization of Radio Lobe Magnetic Fields by Driven Relaxation

Tang

2008

ApJ

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In active galaxies, minimum energy estimates based on the observed radio emission suggest that 10% or more of the total gravitational energy released by the collapse of a supermassive black hole is deposited into lobe-scale magnetic fields and relativistic particles, roughly in equipartition. It is proposed here that the underlying physical process inside the lobe is magnetic self-organization by driven relaxation, rather than a traditional magnetohydrodynamic dynamo. There are two forms of magnetic self-organization. The extreme form of Taylor relaxation is similar to a driven harmonic oscillator, in which a resonance in spatial frequency constrains the input magnetic energy and helicity to the lowest order relaxation mode, commonly known as a spheromak in laboratory plasmas. The general form of magnetic self-organization takes into account the intrinsic nonlinearity of a driven plasma, which can access relaxed states beyond the spheromak resonance. This is a particularly useful physics description for radio lobe plasmas, which are likely overdriven. The degrees of self-organization can be quantified by a spectral energy analysis over the spatial distribution of the magnetic field. The preferred self-organized states can be characterized by a principal component analysis using a projection onto the fundamental relaxation modes that are unique to a given radio lobe morphology.

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“…Since relaxation operates on a shorter time scale, the spheromak configuration is maintained regardless of the details of the specific helicity injection mechanism. Some particular examples are the coaxial helicity injection method (CHI) [4][5][6], the merging of helicitycarrying filaments (MHF) [7] and the helicity injected torus with steady inductive helicity injection (HIT-SI) [8].In this Letter we report the first evidence coming from nonlinear, resistive, 3D MHD numerical simulations that demonstrate the possibility of forming and sustaining a spheromak by forcing tangential flows at the plasma boundary. The method can by explained in terms of helicity injection and differs from other helicity injection methods employed in the past (CHI, MHF and HIT-SI).…”

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confidence: 91%

Spheromak formation and sustainment by tangential boundary flows

García-Martínez

Farengo

2010

Physics of Plasmas

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The nonlinear, resistive, 3D magnetohydrodynamic equations are solved numerically to demonstrate the possibility of forming and sustaining a spheromak by forcing tangential flows at the plasma boundary. The method can by explained in terms of helicity injection and differs from other helicity injection methods employed in the past. Several features which were also observed in previous dc helicity injection experiments are identified and discussed.Spheromak plasmas have been formed using several different techniques [1,2]. The existence of multiple formation methods clearly shows that the spheromak is a preferred (lowest energy) state toward which a magnetohydrodynamic (MHD) system naturally evolves when the appropriate boundary conditions are imposed. The physical process responsible for the formation is magnetic relaxation: on the time scale of MHD instabilities the plasma relaxes to the minimum energy state compatible with its magnetic helicity content (which remains approximately constant) [3]. Once formed, the spheromak will decay in a resistive time scale because resistivity does dissipate magnetic helicity. For this reason, the sustainment of the configuration during times longer than the resistive decay time requires some helicity injection method. Since relaxation operates on a shorter time scale, the spheromak configuration is maintained regardless of the details of the specific helicity injection mechanism. Some particular examples are the coaxial helicity injection method (CHI) [4][5][6], the merging of helicitycarrying filaments (MHF) [7] and the helicity injected torus with steady inductive helicity injection (HIT-SI) [8].In this Letter we report the first evidence coming from nonlinear, resistive, 3D MHD numerical simulations that demonstrate the possibility of forming and sustaining a spheromak by forcing tangential flows at the plasma boundary. The method can by explained in terms of helicity injection and differs from other helicity injection methods employed in the past (CHI, MHF and HIT-SI).An enhanced helicity injection mode was recently reported in spheromak experiments with large plasma rotation [9]. Althought not analyzed in terms of boundary flows, this observation could support the feasibility of the mechanism proposed and studied in this Letter.We model the plasma using the resistive MHD equations with finite viscosity and zero β. The evolution equations for u and B are:where E = −u × B + ηJ and Π = (∇u + ∇u T ) − (2/3) × (∇·u) (see Ref.[10] for further details). These equations are normalized with a (chamber radius), ψ G (imposed flux) and c A (Alfvèn speed). In addition, B and J are scaled with √ µ 0 . Time is expressed in units of the Alfvèn time τ A = a/c A . The normalized resistivity η and the kinematic viscosity ν are set to 5 × 10 −5 . With these values the resistive time is τ r ∼ 800 (defined as in Ref.[11]). The resulting system is solved with the Versatile Advection Code [12].The domain is a cylinder of elongation h/a = 1, with perfectly conducting wall conditions (B · n = 0 ...

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Spheromak Formation by Steady Inductive Helicity Injection

Cited by 42 publications

References 28 publications

Observation of a nonaxisymmetric magnetohydrodynamic self-organized state

Observation of a nonaxisymmetric magnetohydrodynamic self-organized state

Self‐Organization of Radio Lobe Magnetic Fields by Driven Relaxation

Spheromak formation and sustainment by tangential boundary flows

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