Experiments and Observations on Intense Alfvén Waves in the Laboratory and in Space

Gekelman, Walter; Vanzeeland, M.; Vincena, Steve; Pribyl, P.

doi:10.1063/1.1593952

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“…Extensive work on Alfvén wave propagation has been performed in the LArge Plasma Device (LAPD) facility at UCLA. [12] LAPD investigations into Alfvén wave topics as diverse as the propagation of Alfvén waves in expanding plasmas; [13] the behavior of Alfvén waves near the ion cyclotron frequency; [14] the motion of ions in response to a shear Alfvén wave; [15] and shear Alfvén wave propagation from the kinetic to the inertial regime [16] have all been reported. The plasma density in the LAPD system is on the order of 10 12 cm −3 , which yields an Alfvén wavelength on the order of 10 m. LAPD is approximately 17 m in length, which makes laboratory investigation of Alfvén waves possible in a plasma of that density.…”

Section: Introductionmentioning

confidence: 99%

Alfven Wave Propagation in Inhomogeneous Plasmas

Sears¹

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Damping of Alfvén waves is one of the most likely mechanisms for ion heating in the solar corona. Density gradients have significant but poorlyunderstood effects on energy transfer and Alfvén wave propagation in partially ionized plasmas, such as those found in the solar chromosphere. Reflection of Alfvén waves at density and magnetic field gradients can give rise to turbulence which sustains particle heating. [1],[2] The density profile in the Hot hELIcon eXperiment (HELIX) varies strongly with radius, giving access to a wide range of Alfvén dynamics across the plasma column and providing an ideal environment to observe Alfvén wave-driven particle heating. A new internal wave-launching antenna, situated at the edge of the highdensity core and the density-gradient region of HELIX has been used to excite low-frequency waves in argon plasma. The propagation behavior of the launched waves was measured with a small-scale (smaller than the ion gyroradius) magnetic sense coil at multiple radial locations across the plasma column (from the high-density core through the density gradient region). Time-resolved laser induced fluorescence (LIF) and Langmuir probe measurements also yield insight into the plasma response to the perturbation. This dissertation presents cross-spectral and wavelet analysis of low-frequency waves in a helicon plasma with a strong density gradient. Building on the work of Houshmandyar, [3] shear Alfvén waves were launched in a helicon plasma source with a strong density gradient. Alfvén wave turbulence is suggested from phase angle and wavelet analysis of magnetic sense coil probe measurements. The perturbation wavelength derived from phase angle measurements is consistent with predictions from the full Alfvén wave dispersion relation (taking electron Landua damping, electron-ion collisions, and finite frequency effects into account). Time-resolved LIF measurements across the plasma column suggest ion heating where the turbulence is strongest. Timeresolved Langmuir probe measurements show electron heating in response to the launched Alfvén waves. This work is dedicated to the spirit of Shakespeare's sister and every woman who has ever worked to build a room of her own.

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Section: Introductionmentioning

confidence: 99%

Alfven Wave Propagation in Inhomogeneous Plasmas

Sears¹

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Experiments and Observations on Intense Alfvén Waves in the Laboratory and in Space

Cited by 1 publication

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Alfven Wave Propagation in Inhomogeneous Plasmas

Alfven Wave Propagation in Inhomogeneous Plasmas

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