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Title: Turbulent fluctuations during pellet injection into a dipole confined plasma torus

Here, we report measurements of the turbulent evolution of the plasma density profile following the fast injection of lithium pellets into the Levitated Dipole Experiment (LDX) [Boxer et al., Nat. Phys. 6, 207 (2010)]. As the pellet passes through the plasma, it provides a significant internal particle source and allows investigation of density profile evolution, turbulent relaxation, and turbulent fluctuations. The total electron number within the dipole plasma torus increases by more than a factor of three, and the central density increases by more than a factor of five. During these large changes in density, the shape of the density profile is nearly “stationary” such that the gradient of the particle number within tubes of equal magnetic flux vanishes. In comparison to the usual case, when the particle source is neutral gas at the plasma edge, the internal source from the pellet causes the toroidal phase velocity of the fluctuations to reverse and changes the average particle flux at the plasma edge. An edge particle source creates an inward turbulent pinch, but an internal particle source increases the outward turbulent particle flux. Statistical properties of the turbulence are measured by multiple microwave interferometers and by an array of probes atmore » the edge. The spatial structures of the largest amplitude modes have long radial and toroidal wavelengths. Estimates of the local and toroidally averaged turbulent particle flux show intermittency and a non-Gaussian probability distribution function. The measured fluctuations, both before and during pellet injection, have frequency and wave number dispersion consistent with theoretical expectations for interchange and entropy modes excited within a dipole plasma torus having warm electrons and cool ions.« less
Authors:
ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ;  [2] ; ORCiD logo [2]
  1. Columbia Univ., New York, NY (United States). Dept. of Applied Physics and Applied
  2. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
Publication Date:
Grant/Contract Number:
FG02-00ER54585; PHY-1201896
Type:
Published Article
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 1; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Research Org:
Columbia Univ., New York, NY (United States)
Sponsoring Org:
USDOE; National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; Thermodynamic functions; Turbulent flows; Ionospheric physics; Turbulence measurement; Optical metrology; Plasma confinement; Ionospheric dynamics; Toroidal plasma confinement; Magnetospheric dynamics; Fluid flows
OSTI Identifier:
1361733
Alternate Identifier(s):
OSTI ID: 1420487; OSTI ID: 1429074

Garnier, D. T., Mauel, M. E., Roberts, T. M., Kesner, J., and Woskov, P. P.. Turbulent fluctuations during pellet injection into a dipole confined plasma torus. United States: N. p., Web. doi:10.1063/1.4973828.
Garnier, D. T., Mauel, M. E., Roberts, T. M., Kesner, J., & Woskov, P. P.. Turbulent fluctuations during pellet injection into a dipole confined plasma torus. United States. doi:10.1063/1.4973828.
Garnier, D. T., Mauel, M. E., Roberts, T. M., Kesner, J., and Woskov, P. P.. 2017. "Turbulent fluctuations during pellet injection into a dipole confined plasma torus". United States. doi:10.1063/1.4973828.
@article{osti_1361733,
title = {Turbulent fluctuations during pellet injection into a dipole confined plasma torus},
author = {Garnier, D. T. and Mauel, M. E. and Roberts, T. M. and Kesner, J. and Woskov, P. P.},
abstractNote = {Here, we report measurements of the turbulent evolution of the plasma density profile following the fast injection of lithium pellets into the Levitated Dipole Experiment (LDX) [Boxer et al., Nat. Phys. 6, 207 (2010)]. As the pellet passes through the plasma, it provides a significant internal particle source and allows investigation of density profile evolution, turbulent relaxation, and turbulent fluctuations. The total electron number within the dipole plasma torus increases by more than a factor of three, and the central density increases by more than a factor of five. During these large changes in density, the shape of the density profile is nearly “stationary” such that the gradient of the particle number within tubes of equal magnetic flux vanishes. In comparison to the usual case, when the particle source is neutral gas at the plasma edge, the internal source from the pellet causes the toroidal phase velocity of the fluctuations to reverse and changes the average particle flux at the plasma edge. An edge particle source creates an inward turbulent pinch, but an internal particle source increases the outward turbulent particle flux. Statistical properties of the turbulence are measured by multiple microwave interferometers and by an array of probes at the edge. The spatial structures of the largest amplitude modes have long radial and toroidal wavelengths. Estimates of the local and toroidally averaged turbulent particle flux show intermittency and a non-Gaussian probability distribution function. The measured fluctuations, both before and during pellet injection, have frequency and wave number dispersion consistent with theoretical expectations for interchange and entropy modes excited within a dipole plasma torus having warm electrons and cool ions.},
doi = {10.1063/1.4973828},
journal = {Physics of Plasmas},
number = 1,
volume = 24,
place = {United States},
year = {2017},
month = {1}
}