Confinement of test particles in a Malmberg–Penning trap with a biased axial wire

Eggleston, D. L.

doi:10.1063/1.872299

Cited by 38 publications

(26 citation statements)

References 13 publications

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“…In short, we have constructed a trap where the electrons will act as test particles moving in the prescribed fields. Despite these changes, the confinement time scaling with no applied asymmetries [17] shows the same (L/B z ) 2 dependence found in higher density experiments [1,2], supporting the notion that the radial transport is primarily a single particle effect.…”

Section: Asymmetry-induced Transport Theory and Experimental Approachsupporting

confidence: 72%

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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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Section: Asymmetry-induced Transport Theory and Experimental Approachsupporting

confidence: 72%

“…(4), often only one of these peaks will be sizable. The remaining features of the trap have been discussed in detail elsewhere [17,18]. Electrons injected into the trap from an off-axis gun are quickly dispersed into an annular distribution.…”

Section: Asymmetry-induced Transport Theory and Experimental Approachmentioning

confidence: 99%

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

Eggleston¹

2003

AIP Conference Proceedings

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“…The asymmetry potential within the confinement region is thus essentially the vacuum potential and we need not be concerned with plasma modifications of the asymmetry potential. Despite these changes in the plasma parameters, the confinement time scaling with no applied asymmetries [10] shows the same (L/B) 2 dependence found in higher density experiments [11,12], thus supporting the notion that the asymmetry-induced transport is a single particle effect.…”

Section: Resultssupporting

confidence: 55%

Amplitude scaling of asymmetry-induced transport

Eggleston¹,

Carrillo²

2002

AIP Conference Proceedings

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Abstract. Our initial experiments on asymmetry-induced transport in non-neutral plasmas found the radial particle flux at small radii to be proportional to 02, where 0. is the applied asymmetry amplitude. Other researchers, however, using the global expansion rate as a measure of the transport, have observed a €1 scaling when the rigidity (the ratio of the axial bounce frequency to the azimuthal rotation frequency) is in the range one to ten. In an effort to resolve this discrepancy, we have extended our measurements to different radii and asymmetry frequencies. Although the results to date are generally in agreement with those previously reported (0' scaling at low asymmetry amplitudes falling off to a weaker scaling at higher amplitudes), we have observed some cases where the low amplitude scaling is closer to q1. Both the 0' and 0' cases, however, have rigidities less than ten. Instead, we find that the q5l cases are characterized by an induced flux that is comparable in magnitude but opposite in sign to the background flux. This suggests that the mixing of applied and background asymmetries plays an important role in determining the amplitude scaling of this transport.

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“…Nonneutral plasmas are studied in research to develop atomic clocks [8][9][10] , investigations of turbulence, nonlinear vortex dynamics, and instabilities in nearly-inviscid two-dimensional fluids [11][12][13][14][15][16][17][18] , research on particle transport across magnetic field lines in quiescent plasmas [19][20][21][22][23] , investigations of the properties of nonneutral plasmas in thermal equilibrium 24,25 , and in experiments to study the formation and confinement of positron plasmas [26][27][28] . Many of these experiments 8,13,19,[24][25][26] are performed at vacuum pressures in the range where background neutrals are observed to affect the plasma dynamical behavior and confinement properties.…”

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Expansion rate measurements at moderate pressure of non-neutral electron plasmas in the Electron Diffusion Gauge (EDG) experiment

et al. 2001

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Measurements of the expansion rate of pure-electron plasmas have been performed on the Electron Diffusion Gauge (EDG) device at background helium gas pressures in the 5×10 −8 Torr to 1×10 −5 Torr range, where plasma expansion due to electron-neutral collisions dominates over plasma expansion due to trap asymmetries. It is found that the expansion rate, defined as the time rate of change of the particles' mean-square radius, scales approximately linearly with pressure and inversely as the square of the magnetic field strength in this regime, in agreement with classical predictions.

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Confinement of test particles in a Malmberg–Penning trap with a biased axial wire

Cited by 38 publications

References 13 publications

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

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

Amplitude scaling of asymmetry-induced transport

Expansion rate measurements at moderate pressure of non-neutral electron plasmas in the Electron Diffusion Gauge (EDG) experiment

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