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Title: Superbanana transport in the collisional heating of a plasma column forced across a squeeze potential

Authors:
 [1]
  1. Department of Physics, UCSD, La Jolla, California 92093, USA
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1410465
Grant/Contract Number:
SC0002451
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 11; Related Information: CHORUS Timestamp: 2017-11-28 09:48:01; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics
Country of Publication:
United States
Language:
English

Citation Formats

Dubin, Daniel H. E.. Superbanana transport in the collisional heating of a plasma column forced across a squeeze potential. United States: N. p., 2017. Web. doi:10.1063/1.5001062.
Dubin, Daniel H. E.. Superbanana transport in the collisional heating of a plasma column forced across a squeeze potential. United States. doi:10.1063/1.5001062.
Dubin, Daniel H. E.. 2017. "Superbanana transport in the collisional heating of a plasma column forced across a squeeze potential". United States. doi:10.1063/1.5001062.
@article{osti_1410465,
title = {Superbanana transport in the collisional heating of a plasma column forced across a squeeze potential},
author = {Dubin, Daniel H. E.},
abstractNote = {},
doi = {10.1063/1.5001062},
journal = {Physics of Plasmas},
number = 11,
volume = 24,
place = {United States},
year = 2017,
month =
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on November 28, 2018
Publisher's Accepted Manuscript

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  • This paper discusses a novel 'chaotic' form of superbanana transport and compares the theory to experiments on non-neutral plasmas. Superbanana transport is caused by particles that cross local trapping separatrices (magnetic or electric ripples) in the presence of field 'errors' such as toroidal magnetic curvature. Traditionally, collisions (at rate {nu}) cause separatrix crossings, with resulting transport that scales as {nu}{sup 1/2}B{sup -1/2}. The 'chaotic' transport of interest here occurs when the separatrix is 'ruffled' in the direction of plasma drift; then, collisionless particle orbits give random trapping and detrapping. Prior theory assumed a 'stellarator symmetry' and suggested that these orbitsmore » give reduced transport scaling as {nu}{sup p} with p{approx}1. Here, we fully characterize chaotic transport and show that the transport is enhanced rather than reduced, scaling as {nu}{sup 0}B{sup -1}. Experiments on pure electron plasmas provide quantitative transport measurements, with precise control of the overall field error, and of the trapping separatrix with and without ruffles. The experiments show close agreement with theory over a decade in B, for both collisional neoclassical transport, and for the distinctive chaotic transport. At low magnetic fields, transport scaling as B{sup -p} with p>rsim2 becomes dominant, showing preliminary agreement with bounce-resonant theory.« less
  • The so-called superbanana diffusion and thermal conductivity in torsatron stellarator is studied. (AIP)
  • An analytic expression for the neoclassical flux valid in both a multiple-helicity torsatron and a bumpy torus in the superbanana plateau regime is obtained. The expression is valid for arbitrary values of Phi', the radial electric field, partialepsilon/sub H//partialr with epsilon/sub H/ the effective helical modulation or bumpiness, and partialepsilon/sub T//partialr with epsilon/sub T/ the effective toroidal modulation. When small mirror force terms are included in the flux, a nonlinear first-order ordinary differential equation in Phi' is obtained from the ambipolarity relationship.
  • The collisional damping of electron plasma waves (or Trivelpiece-Gould waves) on a pure electron plasma column is discussed. The damping in a pure electron plasma differs from that in a neutral plasma, since there are no ions to provide collisional drag. A dispersion relation for the complex wave frequency is derived from Poisson's equation and the drift-kinetic equation with the Dougherty collision operator--a Fokker-Planck operator that conserves particle number, momentum, and energy. For large phase velocity, where Landau damping is negligible, the dispersion relation yields the complex frequency {omega}=(k{sub z}{omega}{sub p}/k)[1+(3/2)(k{lambda}{sub D}){sup 2}(1+10i{alpha}/9)(1+2i{alpha}){sup -}{sup 1}], where {omega}{sub p} is themore » plasma frequency, k{sub z} is the axial wavenumber, k is the total wavenumber, {lambda}{sub D} is the Debye length, {nu} is the collision frequency, and {alpha}{identical_to}{nu}k/{omega}{sub p}k{sub z}. This expression spans from the weakly collisional regime ({alpha}<<1) to the moderately collisional regime ({alpha}{approx}1) and in the weakly collisional limit yields a damping rate which is smaller than that for a neutral plasma by the factor k{sup 2}{lambda}{sub D}{sup 2}<<1. In the strongly collisional limit ({alpha}>>1), the damping is enhanced by long-range interactions that are not present in the kinetic theory (which assumes pointlike interactions); the effect of these long-range collisions on the damping is discussed.« less