Amplitude scaling of asymmetry-induced transport in a non-neutral plasma trap

Eggleston, D. L.; Carrillo, Brenda

doi:10.1063/1.1436493

Cited by 22 publications

(17 citation statements)

References 10 publications

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“…Once the base pressure is low enough to minimize electron-neutral transport, the confinement is limited by electric and magnetic fields that break the cylindrical symmetry of the trap and produce radial drifts. This asymmetryinduced transport has been studied experimentally by a number of people, [1][2][3][4][5][6][7][8][9] but detailed comparisons of the predictions of resonant particle transport theory 10 with experiment 7 show serious discrepancies. It seems clear that some important physics is missing from the theory.…”

Section: Introductionmentioning

confidence: 96%

Two sources of asymmetry-induced transport

Eggleston

2012

Physics of Plasmas

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A single-particle computer code with collisional effects is used to study asymmetry-induced radial transport of a non-neutral plasma in a coaxial Malmberg-Penning trap. Following the time variation of the mean change and mean square change in radial position allows for the calculation of the radial drift velocity v D and the diffusion coefficient D as defined by the radial flux equationFor asymmetries of the form / 1 ðrÞcosðkz þ xt À lhÞ and periodic boundary conditions, the transport coefficients obtained match those predicted by resonant particle transport theory where the transport is produced by particles with velocities near 6ðlx R À xÞ=k, with x R being the azimuthal rotation frequency. For asymmetries of the form / 1 ðrÞcosðkzÞcosðxt À lhÞ and low collision frequency, there is a second contribution to the transport produced by low velocity particles axially trapped in the asymmetry potential. These produce a stronger variation of D with x with a peak at x ¼ x R . The width of the peak Dx increases with center conductor bias and decreases with radius, while the height shows the opposite behavior. The transport due to axially trapped particles is typically comparable to or larger than that from resonant particles. This second contribution to the transport may explain the discrepancies between experiments and resonant particle theory. V C 2012 American Institute of Physics. [http://dx.

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Section: Introductionmentioning

confidence: 96%

Two sources of asymmetry-induced transport

Eggleston

2012

Physics of Plasmas

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“…[1][2][3][4][5][6][7][8][9] While it is straightforward to observe this transport in experiments, a full understanding of the transport remains elusive. It is well established that electric and magnetic fields that break the cylindrical symmetry of these traps produce radial transport.…”

Section: Introductionmentioning

confidence: 99%

Particle dynamics in asymmetry-induced transport

Eggleston¹

2007

Physics of Plasmas

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The particle dynamics of asymmetry-induced transport are studied using a single-particle computer simulation. For the case of a helical asymmetry with axial and azimuthal wavenumbers (k,l) and with periodic boundary conditions, behaviors consistent with analytical theory are observed. For the typical experimental case of a standing wave asymmetry, the code reveals dynamical behaviors not included in the analytical theory of this transport. The resonances associated with the two constituent helical waves typically overlap and produce a region of stochastic motion. In addition, particles near the radius where the asymmetry frequency ω matches l times the E×B rotation frequency ωR can be trapped in the potential of the applied asymmetry and confined to one end of the device. Both behaviors are associated with large radial excursions and mainly affect particles with low velocities, i.e., vz<2ωT∕k, where ωT is the trapping frequency. For the case of a helical asymmetry with specularly reflecting boundaries, large radial excursions are observed for all velocities near the radius, where ω=lωR. Minor modifications to these results are observed when the code is run with realistic end potentials.

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“…The plateau regime flux is proportional to the square of the asymmetry amplitude φ 2 nlω . Our previous studies of the amplitude scaling [8] of this transport suggest that we are in the plateau regime, but the results of this paper are not dependent upon that identification because both the plateau regime and the banana regime suitable for higher asymmetry amplitudes have the same frequency dependence. The previously mentioned domination of the transport by resonant particles is reflected in the e −x 2 factor, which stems from evaluating the Maxwellian distribution function at the resonant velocity.…”

Section: Asymmetry-induced Transport Theory and Experimental Approachmentioning

confidence: 55%

“…Such asymmetries produce a radial component to the E × B or grad-B drift that leads to particle loss. This basic understanding is supported by confinement studies [1,2] as well as experiments with applied electric [3,4,5,6,7,8] and magnetic [9,10] asymmetries.…”

Section: Introductionmentioning

confidence: 81%

Using Variable Frequency Asymmetries to Understand Radial Transport in a Malmberg-Penning Trap

Eggleston¹

2003

AIP Conference Proceedings

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It has long been known that asymmetric electric and magnetic fields produce radial transport in Malmberg-Penning traps, and much work has been done to understand this transport. Our approach is to apply a variable frequency electric asymmetry to a low density population of electrons and to measure the resulting radial particle flux Γ as a function of radius r. The low particle density eliminates many plasma modes (which have their own frequency dependence) and allows us to focus on the transport physics. The usual azimuthal E × B drift is maintained by a biased central wire, and this arrangement also allows us to independently vary the drift frequency ω R by adjusting either the axial magnetic field B z or the bias of the central wire φ cw . Up to forty wall sectors are used in order to apply an asymmetry consisting of a single fourier mode (n, l, ω), where n is the axial wavenumber, l is the azimuthal wavenumber, and ω is the asymmetry frequency. In the current experiments, we vary ω, n, φ cw , and B z . As ω is varied, the particle flux shows a resonance similar to that predicted by resonant particle theory. The peak frequency of this resonance f peak increases with ω R and varies with n, in qualitative agreement with theory, but when quantitative comparisons are made the experimental values for f peak do not match those predicted by theory. Instead, the dependence of f peak on φ cw , B z , and r follows simple empirical scaling laws: for inward directed flux, f peak (MHz) ≈ [−Rφ cw (V)/rB z (G)] 1/2 , where R is the wall radius, and for outward directed flux, f peak (MHz) ≈ 0.8[−φ cw (V)/B z (G)] 1/2 . These results may provide guidance for the construction of the correct theory of asymmetry-induced transport.

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Amplitude scaling of asymmetry-induced transport in a non-neutral plasma trap

Cited by 22 publications

References 10 publications

Two sources of asymmetry-induced transport

Two sources of asymmetry-induced transport

Particle dynamics in asymmetry-induced transport

Using Variable Frequency Asymmetries to Understand Radial Transport in a Malmberg-Penning Trap

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