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

Abstract

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:

Garnier, D. T.  ^[1];

• Search DOE PAGES for author "Garnier, D. T."
• Search DOE PAGES for ORCID "0000-0002-0718-1073"

Mauel, M. E.  ^[1];

• Search DOE PAGES for author "Mauel, M. E."
• Search DOE PAGES for ORCID "0000-0003-2490-7478"

Roberts, T. M.  ^[1];

• Search DOE PAGES for author "Roberts, T. M."
• Search DOE PAGES for ORCID "0000-0003-1964-7683"

Kesner, J. ^[2]; Woskov, P. P.  ^[2]

• Search DOE PAGES for author "Woskov, P. P."
• Search DOE PAGES for ORCID "0000-0002-1148-9345"

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+ Show Author Affiliations

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:

Tue Jan 17 00:00:00 EST 2017

Research Org.:

Columbia Univ., New York, NY (United States)

Sponsoring Org.:

USDOE; National Science Foundation (NSF)

OSTI Identifier:

1361733

Alternate Identifier(s):

OSTI ID: 1420487; OSTI ID: 1429074

Grant/Contract Number:  

FG02-00ER54585; PHY-1201896

Resource Type:

Published Article

Journal Name:

Physics of Plasmas

Additional Journal Information:

Journal Name: Physics of Plasmas Journal Volume: 24 Journal Issue: 1; Journal ID: ISSN 1070-664X

Publisher:

American Institute of Physics (AIP)

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