Spectral gap of shear Alfvén waves in a periodic array of magnetic mirrors

Zhang, Yang; Heidbrink, W. W.; Boehmer, H.; McWilliams, R.; Chen, Guangye; Breǐzman, B. N.; Vincena, S.; Carter, Troy; Leneman, D.; Gekelman, Walter; Pribyl, Patrick; Brugman, B.

doi:10.1063/1.2827518

Cited by 35 publications

(87 citation statements)

References 42 publications

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“…When a spectrum of Alfvén waves is considered, White et al (2002) demonstrated that the amplitude threshold of the Alfvén waves for ion stochastic heating can be significantly decreased. Evidences of ion heating by low-frequency Alfvén waves have also been found in laboratory experiments (Gates et al 2001;Fredrickson et al 2002;Zhang et al 2008).…”

Section: Introductionmentioning

confidence: 62%

Ion Heating by a Spectrum of Obliquely Propagating Low-Frequency Alfvén Waves

Chen

2009

ApJ

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Ion stochastic heating by a monochromatic Alfvén wave, which propagates obliquely to the background magnetic field, has been studied by Chen et al. It is shown that ions can be resonantly heated at frequencies a fraction of the ion cyclotron frequency when the wave amplitude is sufficiently large. In this paper, the monochromatic wave is extended to a spectrum of left-hand polarized Alfvén waves. When the amplitude of the waves is small, the components of the ion velocity have several distinct frequencies, and their motions are quasi-periodic. However, when the amplitude of the waves is sufficiently large, the components of the ion velocity have a spectrum of continuous frequencies near the ion cyclotron frequency due to the nonlinear coupling between the Alfvén waves and the ion gyromotion, and the ion motions are stochastic. Compared with the case of a monochromatic Alfvén wave, the threshold of the ion stochastic heating by a spectrum of Alfvén waves is much lower. Even when their frequencies are only several percent of the ion cyclotron frequency, the ions can also be stochastically heated. The relevance of this heating mechanism to solar corona is also discussed.

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Section: Introductionmentioning

confidence: 62%

Ion Heating by a Spectrum of Obliquely Propagating Low-Frequency Alfvén Waves

Chen

2009

ApJ

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“…Monochromatic signals or pulses can be applied. It is well known 36,37 that in cylindrical plasmas with a vacuum (or low density) gap between the main plasma and the vacuum vessel, there is the possibility of exciting radial eigenmodes of the fast (compressional) Alfv en wave; however, previous experiments in LAPD using similar antennas in plasmas with either a single ion species, [38][39][40] or two ion species, 30,31 have not observed such modes to be excited in the explored range of frequencies.…”

Section: Methodsmentioning

confidence: 97%

Investigation of an ion-ion hybrid Alfvén wave resonator

et al. 2013

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A theoretical and experimental investigation is made of a wave resonator based on the concept of wave reflection along the confinement magnetic field at a spatial location where the wave frequency matches the local value of the ion-ion hybrid frequency. Such a situation can be realized by shear Alfv en waves in a magnetized plasma with two ion species because this mode has zero parallel group velocity and experiences a cut-off at the ion-ion hybrid frequency. Since the ion-ion hybrid frequency is proportional to the magnetic field, it is expected that a magnetic well configuration in a two-ion plasma can result in an Alfv en wave resonator. Such a concept has been proposed in various space plasma studies and could have relevance to mirror and tokamak fusion devices. This study demonstrates such a resonator in a controlled laboratory experiment using a H þ -He þ mixture. The resonator response is investigated by launching monochromatic waves and impulses from a magnetic loop antenna. The observed frequency spectra are found to agree with predictions of a theoretical model of trapped eigenmodes. V C 2013 American Institute of Physics.

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“…A compound antenna consisting of two rectangular current-carrying straps isolated from each other and the plasma 18,19 is inserted into the plasma at the far end of the depletion, 16 m from the plasma source. The antenna is centered on the depletion with the longer current-carrying straps parallel to the background magnetic field B 0 [see Fig.…”

Section: Nonlinear Beat Wave Interaction Among Alfvén Wavesmentioning

confidence: 99%

Resonant drive and nonlinear suppression of gradient-driven instabilities via interaction with shear Alfvén waves

et al. 2011

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The nonlinear interaction of shear Alfvén waves and gradient-driven instabilities on pressure gradients in the Large Plasma Device (LAPD) [Gekelman et al., Rev. Sci. Instrum. 62, 2875] at UCLA is explored. Nonlinear response at the beat frequency between two shear Alfvén waves is shown to resonantly drive unstable modes as well as otherwise damped modes. Resonantly driving the damped modes is shown to suppress the originally unstable mode, leaving only the beat-driven response with an overall reduction in fluctuation amplitude. A threshold is observed in the suppression behavior, requiring that the driven damped mode power be of order 10% of the power in the saturated unstable mode. The interaction is also observed to be dependent on the parallel wavenumber of the driven beat wave; efficient coupling and suppression is only observed for co-propagating beat waves with small parallel wavenumber, consistent with the parallel wavenumber of the gradient-driven modes.

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Spectral gap of shear Alfvén waves in a periodic array of magnetic mirrors

Cited by 35 publications

References 42 publications

Ion Heating by a Spectrum of Obliquely Propagating Low-Frequency Alfvén Waves

Ion Heating by a Spectrum of Obliquely Propagating Low-Frequency Alfvén Waves

Investigation of an ion-ion hybrid Alfvén wave resonator

Resonant drive and nonlinear suppression of gradient-driven instabilities via interaction with shear Alfvén waves

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