The relationship between the 'tangled discharge' and 'dynamo' models of the magnetic relaxation process

Rusbridge, M G

doi:10.1088/0741-3335/33/12/004

Cited by 27 publications

(26 citation statements)

References 16 publications

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“…The large scale magnetic chaos of multiple helicity states has an interesting consequence, as was shown by Rusbridge [61] on the basis of an idea by Kadomtsev and Moffatt: (i) In the radial domain where the magnetic field is chaotic, transport is fast, and the equilibrium is almost force-free; therefore J = μB where μ may be space-dependent. (ii) Setting this in ∇ · J = 0, implies ∇μ · B = 0, which shows that μ must be constant along field lines; thus μ is constant in the chaotic radial domain.…”

Section: Multiple Helicitymentioning

confidence: 98%

What is a Reversed Field Pinch?

Escande¹

2015

Rotation and Momentum Transport in Magnetized Plasmas

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Section: Multiple Helicitymentioning

confidence: 98%

What is a Reversed Field Pinch?

Escande¹

2015

Rotation and Momentum Transport in Magnetized Plasmas

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“…The first scheme tested, the so-called intelligent-shell (IS) [4], in which the coils are coupled in a feedback scheme with the measurements provided by an identical grid of radial field sensors, improves the plasma performances by preventing the radial field penetration of the shell [5]: besides a complete suppression of the resistive wall modes [6], the TMs edge amplitude is kept at a low value. In RFPs TMs in the non-linear regime are required by the dynamo mechanism in order to maintain the reversed configuration [7,8]. Therefore these perturbations would exist even in the presence of a perfectly conducting shell.…”

Section: Introductionmentioning

confidence: 99%

Beyond the Intelligent-shell Concept: the Clean-mode-control for Tearing Perturbations

Zanca

2010

Plasma and Fusion Research

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The Intelligent Shell scheme, where a grid of active coils counteracts in a feedback scheme the measurements provided by an identical grid of sensors, has shown some limitations in the control of the dynamo tearing modes in RFX-mod. The origin of the problem is the aliasing on the measurements coming from the high periodicity sideband harmonics produced by the discrete nature of the active coils. A more efficient feedback on tearing modes is obtained by removing the sidebands from the measurements, thereby counteracting the true tearing Fourier modes. In this scheme, named Clean-Mode-Control, the sidebands are computed in real time from the coils currents using the cylindrical geometry approximation. The Clean-Mode-Control significantly alleviates the wall-locking of tearing modes in RFX-mod, giving the possibility of operating at a plasma current (1.5 MA) never reached before in a RFP machine. These features are well explained by a MHD model describing the tearing mode dynamic under the viscous torque due to the fluid motion and the electromagnetic torques produced by the feedback, the conductive structures surrounding the plasma and the non-linear interaction between the different modes [P. Zanca, Plasma Phys. Control. Fusion 51, No. 1, 015006 (2009)]. Here some new results obtained with this model are discussed. In particular we will show that the edge radial field control improves by reducing the ratio between the delay introduced by the digital acquisition of the measurements and the time constant of the shell that contains the plasma. In this formulation the active coils are assumed to be located outside the shell.

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“…Three theories have been proposed: the tangled discharge model or TDM [4], the magnetohydrodynamic (MHD) dynamo [5,6], and the kinetic dynamo theory or KDT [7]. In MHD dynamo theories the current drive is attributed to the eff'ect of fluctuations through the (vxb) term in Ohm's law (where v and b are the fluctuating parts of the velocity and magnetic field in the plasma), and it has recently been shown [8] that the same is true for the TDM; on the other hand, the KDT relies on an eff*ective nonlocal conductivity due to current diff'usion arising from magnetic fluctuations.…”

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confidence: 99%

Observations of the magnetohydrodynamic dynamo effect in a spheromak plasma

et al. 1993

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We present measurements of the magnetohydrodynamic ''dynamo" due to correlated fluctuations of velocity and magnetic field in the SPHEX spheromak. We show that there are both single-mode and turbulent dynamo processes present, although the single-mode process is in this case an "antidynamo" opposing the externally applied electric field. The size of the turbulent dynamo at the magnetic axis is close to that required to drive the toroidal current there.

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The relationship between the 'tangled discharge' and 'dynamo' models of the magnetic relaxation process

Cited by 27 publications

References 16 publications

What is a Reversed Field Pinch?

What is a Reversed Field Pinch?

Beyond the Intelligent-shell Concept: the Clean-mode-control for Tearing Perturbations

Observations of the magnetohydrodynamic dynamo effect in a spheromak plasma

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