Why Extrap?

Lehnert, B.

doi:10.13182/fst89-a29094

Cited by 26 publications

(7 citation statements)

References 47 publications

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“…These results are consistent with recent experimental observations in the ULQ discharges reported in Refs [8][9][10], as well as with earlier stability studies of screw pinches with particular profiles [21,22]. The influence of a non-circular shape of the plasma cross-section, as for instance in the Extrap configuration [7], is negligible for relatively flat or peaked current profiles. For hollow profiles, a moderate deterioration of the stability occurs.…”

Section: Profile Effectssupporting

confidence: 92%

“…As shown in Refs [16,17], the non-circularity effect, for k <^ 1 and in a high order approximation of the multipole field, can be expressed in terms of a shift = jod - where I c is the current in each of the four rods producing the octupole field, I p is the plasma current, R c is the distance from the axis to the rods and R p is the average radius of the plasma. X is approximately equal to the plasma non-circularity AR p /R p [16] and is in the experiments usually in the range of 1-6% [7]. From Eq.…”

Section: Profile Effectsmentioning

confidence: 97%

“…In the Extrap configuration [7], a magnetic octupole field is added to a screw pinch, producing a non-circular shape of the plasma cross-section. This has a destabilizing effect on the global m = 1 kink mode.…”

Section: Profile Effectsmentioning

confidence: 99%

“…Configurations that (more or less) belong to this category are, for instance, the 'stabilized pinches', the reversed field pinches, the Extrap configuration, the high density Z-pinches and the plasma focus experiments summarized in Refs [4][5][6][7]. In particular, the ultra low q (ULQ) toroidal and linear discharges recently reported by Kamada et al [8] and Brunsell et al [9,10] clearly indicate the existence of parameter regions of improved global stability that are not consistent with the Kruskal-Shafranov condition.…”

Section: Introductionmentioning

confidence: 99%

“…[12] to the case of a completely arbitrary equilibrium magnetic field. Furthermore, we consider here also the effect of a non-circular plasma cross-section, having particularly the Extrap configuration [7] in mind.…”

Section: Introductionmentioning

confidence: 99%

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Current problems in ball lightning science

Smirnov¹

1990

Sov. Phys. Usp.

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An analytical expression for the eigenvalue of the global m = 1 kink mode in a straight screw pinch with arbitrary profiles of current density and axial magnetic field is derived in a long wavelength approximation of the incompressible ideal MHD equations. While the influence of the current profile is related to the inductance t t of the plasma column, as has been shown previously (Nucl. Fusion 24 (

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Section: Profile Effectssupporting

confidence: 92%

Section: Profile Effectsmentioning

confidence: 97%

Section: Profile Effectsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Current problems in ball lightning science

Smirnov¹

1990

Sov. Phys. Usp.

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A numerical study of strongly nonlinear plasma motion in a magnetic octupole field

Eriksson

Wahlberg

1990

J. Plasma Phys.

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The strongly nonlinear axisymmetric motion of a z–pinch in an external magnetic octupole field is investigated numerically. A surface-current ideal-MHD approximation of the pinch is used, which allows a ‘contour-dynamics’ formulation of the problem. It is found that the plasma motion in the strongly nonlinear regime results in a collision between the plasma and one (or several) of the X-points. Thereafter, the X-point splits into two magnetic nulls (Y-points), which remain on the plasma surface and between which current reversal occurs. This phenomenon results in a strong force exerted on the outer parts of the plasma and directed towards the centre of the configuration. The force is able to stop the outward plasma motion under certain parameter conditions, which are found to be similar to those observed in experiments on the straight Extrap configuration.

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Electron plasma oscillations at arbitrary Debye lengths

Lehnert

1991

J. Plasma Phys.

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A solution is presented for electron plasma oscillations in a thermalized plasma, at arbitrary ratios of the Debye length AλD and the perturbation wavelength λ. The limit λD≪λ corresponds to the conventional fluid-like theory of small particle excursions, whereas λD≫λ corresponds to the free-streaming limit of strong kinetic phase mixing due to large particle excursions. A strong large-Debye-distance (LDD) effect already appears when λD ≳ λ. The initial amplitude of the fluid-like contribution to the macroscopic density perturbation then becomes small compared with the contribution from the free-streaming part. As a consequence, only a small fraction of the density perturbation remains after a limited number of kinetic damping times of the free-streaming part. The present analysis can be considered as a first exercise in an attempt to tackle the far more difficult problem of large-Larmor-radius (LLR) effects in a magnetized plasma. The analysis further shows that a representation in terms of normal modes of the form exp (— iωt) leads to amplitude factors of these modes that are related to each other and that depend on the combined free-streaming and fluid behaviour of the plasma. Consequently, these modes are coupled and cannot be treated as independent of each other.

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Why Extrap?

Cited by 26 publications

References 47 publications

Current problems in ball lightning science

Current problems in ball lightning science

A numerical study of strongly nonlinear plasma motion in a magnetic octupole field

Electron plasma oscillations at arbitrary Debye lengths

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