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Impact of the electron density and temperature gradient on drift-wave turbulence in the Large Plasma Device

Published online by Cambridge University Press:  03 August 2022

Conor Perks Open the ORCID record for Conor Perks [Opens in a new window] ,
Saskia Mordijck Open the ORCID record for Saskia Mordijck [Opens in a new window] ,
Troy Carter Open the ORCID record for Troy Carter [Opens in a new window] ,
Bart Van Compernolle Open the ORCID record for Bart Van Compernolle [Opens in a new window] ,
Stephen Vincena Open the ORCID record for Stephen Vincena [Opens in a new window] ,
Giovanni Rossi Open the ORCID record for Giovanni Rossi [Opens in a new window]  and
David Schaffner Open the ORCID record for David Schaffner [Opens in a new window]
Conor Perks
Affiliation:
North Carolina State University, Raleigh, NC, USA
Saskia Mordijck*
Affiliation:
Department of Physics, William & Mary, Williamsburg, VA, USA
Troy Carter
Affiliation:
Department of Physics and Astronomy, UCLA, Los Angeles, CA, USA
Bart Van Compernolle
Affiliation:
General Atomics, San Diego, CA, USA
Stephen Vincena
Affiliation:
Department of Physics and Astronomy, UCLA, Los Angeles, CA, USA
Giovanni Rossi
Affiliation:
Department of Physics and Astronomy, UCLA, Los Angeles, CA, USA
David Schaffner
Affiliation:
Department of Physics, Bryn Mawr College, PA, USA
*
†Email address for correspondence: [email protected]
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Abstract

In this paper we present an experimental study of edge turbulence in the Large Plasma Device at UCLA. We utilize a scan of discharge power and prefill pressure (neutral density) to show experimentally that turbulent density fluctuations decrease with decreasing density gradient, as predicted for resistive drift-wave turbulence (RDWT). As expected for RDWT, we observe that the cross-phase between the density and potential fluctuations is close to 0. Moreover, the addition of an electron temperature gradient leads to a reduction in the amplitude of the density fluctuations, as expected for RDWT. However, counter to theoretical expectations, we find that the potential fluctuations do not follow the same trends as the density fluctuations for changes either in density gradients or the addition of a temperature gradient. The disconnect between the density and potential fluctuations is connected to changes in the parallel flows as a result of differences in the prefill pressure, i.e. neutral density. Further analysis of the density and potential fluctuation spectra show that the electron temperature gradient reduces the low frequency fluctuations up to $10 \,{\rm kHz}$ and the introduction of a temperature gradient leads to an unexpected ${\sim }{\rm \pi}$ shift of the density–potential cross-phase at ${\sim }10\,{\rm kHz}$, while maintaining the typical resistive drift-wave cross-phase at lower frequencies. These experiments partly confirm existing knowledge on resistive drift-wave turbulence, but also introduce new observations that indicate a need for dedicated nonlinear three-dimensional turbulence simulations that include neutrals.

Keywords

plasma dynamicsplasma nonlinear phenomena
Type
Research Article
Information
Journal of Plasma Physics , Volume 88 , Issue 4 , August 2022 , 905880405
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Copyright
Copyright © The Author(s), 2022. Published by Cambridge University Press

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