Measurement of the global structure of interchange modes driven by energetic electrons trapped in a magnetic dipole

Levitt, B.; Maslovsky, D.; Mauel, M. E.

doi:10.1063/1.1475999

Cited by 23 publications

(49 citation statements)

References 38 publications

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“…The hot electron species can be unstable to the hot electron interchange (HEI) [14][15][16] mode when the hot electron density gradient is sufficiently high and the background density is sufficiently low [10]. Similarly to supported mode operation, when the dipole is levitated the plasma entered a high-density regime in which the HEI was stabilized for sufficient gas fueling.…”

Section: Improved Stability To Heimentioning

confidence: 99%

Confinement improvement with magnetic levitation of a superconducting dipole

et al. 2009

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Abstract. We report the first production of high beta plasma confined in a fully levitated laboratory dipole using neutral gas fueling and electron cyclotron resonance heating. The pressure results primarily from a population of energetic trapped electrons that is sustained for many seconds of microwave heating provided sufficient neutral gas is supplied to the plasma. As compared to previous studies in which the internal coil was supported, levitation results in improved particle confinement that allows higher-density, high-beta discharges to be maintained at significantly reduced gas fueling. Elimination of parallel losses coupled with reduced gas leads to improved energy confinement and a dramatic change in the density profile. Improved particle confinement assures stability of the hot electron component at reduced pressure. By eliminating supports used in previous studies, cross-field transport becomes the main loss channel for both the hot and the background species. Interchange stationary density profiles, corresponding to an equal number of particles per flux tube, are commonly observed in levitated plasmas.

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Section: Improved Stability To Heimentioning

confidence: 99%

Confinement improvement with magnetic levitation of a superconducting dipole

et al. 2009

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“…Bounceaveraged drift-resonance couples energy between particles and waves and is essential to understanding radial transport of energetic electrons. 53 Nonlinear turbulent cascade couples turbulent energy from smaller to larger scales, 27 and the linear growth rate cannot be used to determine the saturated turbulent spectrum. Although the measured broad-band driftresonant fluctuations justify a quasilinear representation of transport, 19,21 a fully self-consistent model of interchange and entropy mode driven transport requires nonlinear simulations.…”

Section: -14mentioning

confidence: 99%

“…, (iii) the radial gradient of the flux-tube particle number, h 0 n / @ðn 0 dVÞ=@w, and (iv) the radial gradient of the entropy density, h 0 p / @ðP 0 dV c Þ=@w. The structure of the perturbed potential can be calculated numerically, as in Ref. 53, or parameterized using a local approximation, m 2 ? ¼ m 2 À ðh w i=h u iÞ e U À1 @ 2 e U=@w 2 , where h w i and h u i are the flux-tube average of the product of the plasma dielectric, n 0 M i =B 2 , with jrwj 2 and jruj 2 , respectively.…”

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confidence: 99%

Turbulent fluctuations during pellet injection into a dipole confined plasma torus

et al. 2017

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We report measurements of the turbulent evolution of the plasma density profile following the fast injection of lithium pellets into the Levitated Dipole Experiment (LDX) [Boxer et al., Nat. Phys. 6, 207 (2010)]. As the pellet passes through the plasma, it provides a significant internal particle source and allows investigation of density profile evolution, turbulent relaxation, and turbulent fluctuations. The total electron number within the dipole plasma torus increases by more than a factor of three, and the central density increases by more than a factor of five. During these large changes in density, the shape of the density profile is nearly “stationary” such that the gradient of the particle number within tubes of equal magnetic flux vanishes. In comparison to the usual case, when the particle source is neutral gas at the plasma edge, the internal source from the pellet causes the toroidal phase velocity of the fluctuations to reverse and changes the average particle flux at the plasma edge. An edge particle source creates an inward turbulent pinch, but an internal particle source increases the outward turbulent particle flux. Statistical properties of the turbulence are measured by multiple microwave interferometers and by an array of probes at the edge. The spatial structures of the largest amplitude modes have long radial and toroidal wavelengths. Estimates of the local and toroidally averaged turbulent particle flux show intermittency and a non-Gaussian probability distribution function. The measured fluctuations, both before and during pellet injection, have frequency and wavenumber dispersion consistent with theoretical expectations for interchange and entropy modes excited within a dipole plasma torus having warm electrons and cool ions.

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“…We have solved the above gyrokinetic system Eqs. (5) and (6) in Z-pinch with only passing particles using MGK code in Ref. [25], where we can assume v and v ⊥ to be constant along field line.…”

Section: Linear Gyrokinetic Modelmentioning

confidence: 99%

“…The idea of using strong dipole field configuration for magnetic confinement of laboratory plasmas for fusion is proposed theoretically by Hasegawa [1,2] and several experimental devices have also been built since then, such as the Levitated Dipole Experiment (LDX) [3][4][5] at MIT, the Collisionless Terrella Experiment (CTX) [6] at Columbia University and Ring Trap-1 (RT-1) [7,8] at the University of Tokyo. The dipole configuration is also used to confine electron-positron pair plasmas in the laboratory [9].…”

Section: Introductionmentioning

confidence: 99%

Local gyrokinetic study of electrostatic microinstabilities in dipole plasmas

et al. 2017

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A linear gyrokinetic particle-in-cell scheme, which is valid for arbitrary perpendicular wavelength k ⊥ ρi and includes the parallel dynamic along the field line, is developed to study the local electrostatic drift modes in point and ring dipole plasmas. We find the most unstable mode in this system can be either electron mode or ion mode. The properties and relations of these modes are studied in detail as a function of k ⊥ ρi, the density gradient κn, the temperature gradient κT , electron to ion temperature ratio τ = Te/Ti, and mass ratio mi/me. For conventional weak gradient parameters, the mode is on ground state (with eigenstate number l = 0) and especially k ∼ 0 for small k ⊥ ρi. Thus, bounce averaged dispersion relation is also derived for comparison. For strong gradient and large k ⊥ ρi, most interestingly, higher order eigenstate modes with even (e.g., l = 2, 4) or odd (e.g., l = 1) parity can be most unstable, which is not expected by previous studies. High order eigenstate can also easily be most unstable at weak gradient when τ > 10. This work can be particularly important to understand the turbulent transport in laboratory and space magnetosphere.

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Measurement of the global structure of interchange modes driven by energetic electrons trapped in a magnetic dipole

Cited by 23 publications

References 38 publications

Confinement improvement with magnetic levitation of a superconducting dipole

Confinement improvement with magnetic levitation of a superconducting dipole

Turbulent fluctuations during pellet injection into a dipole confined plasma torus

Local gyrokinetic study of electrostatic microinstabilities in dipole plasmas

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