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Martin MJ, Gekelman W, Van Compernolle B, Pribyl P, Carter T. Experimental Observation of Convective Cell Formation due to a Fast Wave Antenna in the Large Plasma Device. PHYSICAL REVIEW LETTERS 2017; 119:205002. [PMID: 29219335 DOI: 10.1103/physrevlett.119.205002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2017] [Indexed: 06/07/2023]
Abstract
An experiment in a linear device, the Large Plasma Device, is used to study sheaths caused by an actively powered radio frequency (rf) antenna. The rf antenna used in the experiment consists of a single current strap recessed inside a copper box enclosure without a Faraday screen. A large increase in the plasma potential was observed along magnetic field lines that connect to the antenna limiter. The electric field from the spatial variation of the rectified plasma potential generated E[over →]×B[over →]_{0} flows, often referred to as convective cells. The presence of the flows generated by these potentials is confirmed by Mach probes. The observed convective cell flows are seen to cause the plasma in front of the antenna to flow away and cause a density modification near the antenna edge. These can cause hot spots and damage to the antenna and can result in a decrease in the ion cyclotron range of frequencies antenna coupling.
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Affiliation(s)
- M J Martin
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - W Gekelman
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - B Van Compernolle
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - P Pribyl
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - T Carter
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
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Gekelman W, De Haas T, Daughton W, Van Compernolle B, Intrator T, Vincena S. Pulsating Magnetic Reconnection Driven by Three-Dimensional Flux-Rope Interactions. PHYSICAL REVIEW LETTERS 2016; 116:235101. [PMID: 27341240 DOI: 10.1103/physrevlett.116.235101] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Indexed: 06/06/2023]
Abstract
The dynamics of magnetic reconnection is investigated in a laboratory experiment consisting of two magnetic flux ropes, with currents slightly above the threshold for the kink instability. The evolution features periodic bursts of magnetic reconnection. To diagnose this complex evolution, volumetric three-dimensional data were acquired for both the magnetic and electric fields, allowing key field-line mapping quantities to be directly evaluated for the first time with experimental data. The ropes interact by rotating about each other and periodically bouncing at the kink frequency. During each reconnection event, the formation of a quasiseparatrix layer (QSL) is observed in the magnetic field between the flux ropes. Furthermore, a clear correlation is demonstrated between the quasiseparatrix layer and enhanced values of the quasipotential computed by integrating the parallel electric field along magnetic field lines. These results provide clear evidence that field lines passing through the quasiseparatrix layer are undergoing reconnection and give a direct measure of the nonlinear reconnection rate. The measurements suggest that the parallel electric field within the QSL is supported predominantly by electron pressure; however, resistivity may play a role.
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Affiliation(s)
- W Gekelman
- Department of Physics, University of California, Los Angeles, Los Angeles, California 90095, USA
| | - T De Haas
- Department of Physics, University of California, Los Angeles, Los Angeles, California 90095, USA
| | - W Daughton
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - B Van Compernolle
- Department of Physics, University of California, Los Angeles, Los Angeles, California 90095, USA
| | - T Intrator
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - S Vincena
- Department of Physics, University of California, Los Angeles, Los Angeles, California 90095, USA
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Campanell MD, Umansky MV. Strongly Emitting Surfaces Unable to Float below Plasma Potential. PHYSICAL REVIEW LETTERS 2016; 116:085003. [PMID: 26967420 DOI: 10.1103/physrevlett.116.085003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Indexed: 06/05/2023]
Abstract
An important unresolved question in plasma physics concerns the effect of strong electron emission on plasma-surface interactions. Previous papers reported solutions with negative and positive floating potentials relative to the plasma edge. The two models give very different predictions for particle and energy balance. Here we show that the positive potential state is the only possible equilibrium in general. Even if a negative floating potential existed at t=0, the ionization collisions near the surface will force a transition to the positive floating potential state. This transition is demonstrated with a new simulation code.
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Affiliation(s)
- M D Campanell
- Lawrence Livermore National Laboratory, P.O. Box 808(L-630), Livermore, California 94551, USA
| | - M V Umansky
- Lawrence Livermore National Laboratory, P.O. Box 808(L-630), Livermore, California 94551, USA
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Gekelman W, Pribyl P, Lucky Z, Drandell M, Leneman D, Maggs J, Vincena S, Van Compernolle B, Tripathi SKP, Morales G, Carter TA, Wang Y, DeHaas T. The upgraded Large Plasma Device, a machine for studying frontier basic plasma physics. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2016; 87:025105. [PMID: 26931889 DOI: 10.1063/1.4941079] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2015] [Accepted: 01/10/2016] [Indexed: 06/05/2023]
Abstract
In 1991 a manuscript describing an instrument for studying magnetized plasmas was published in this journal. The Large Plasma Device (LAPD) was upgraded in 2001 and has become a national user facility for the study of basic plasma physics. The upgrade as well as diagnostics introduced since then has significantly changed the capabilities of the device. All references to the machine still quote the original RSI paper, which at this time is not appropriate. In this work, the properties of the updated LAPD are presented. The strategy of the machine construction, the available diagnostics, the parameters available for experiments, as well as illustrations of several experiments are presented here.
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Affiliation(s)
- W Gekelman
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095, USA
| | - P Pribyl
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095, USA
| | - Z Lucky
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095, USA
| | - M Drandell
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095, USA
| | - D Leneman
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095, USA
| | - J Maggs
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095, USA
| | - S Vincena
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095, USA
| | - B Van Compernolle
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095, USA
| | - S K P Tripathi
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095, USA
| | - G Morales
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095, USA
| | - T A Carter
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095, USA
| | - Y Wang
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095, USA
| | - T DeHaas
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095, USA
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Bonde J, Vincena S, Gekelman W. Electrostatic structure of a magnetized laser-produced plasma. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 92:051102. [PMID: 26651639 DOI: 10.1103/physreve.92.051102] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/01/2015] [Indexed: 06/05/2023]
Abstract
Measurements of the structure of the electrostatic fields produced by the expansion of a laser-produced plasma into a background magnetized plasma are presented. The three-dimensional measurements of the electrostatic field are made using an emissive probe that measures the time-varying plasma potential on two orthogonal planes, one across and one containing the background magnetic field. The inductive electric field is also calculated from probe measurements of the time-varying magnetic fields. Deviations from local charge neutrality at the level of 10(-4) generate a radial electrostatic field with peak strength an order of magnitude larger than the corresponding inductive field. The electrostatic energy density near full expansion is over an order of magnitude larger than that of the induced azimuthal electric field. These measurements show that electrostatic fields must be included in theoretical and computational models of collisionless coupling in magnetized point explosions of laser-produced plasmas and their relation to similar phenomena such as magnetospheric chemical releases.
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Affiliation(s)
- Jeffrey Bonde
- Department of Physics and Astronomy, University of California, Los Angeles, Los Angeles, California 90095, USA
| | - Stephen Vincena
- Department of Physics and Astronomy, University of California, Los Angeles, Los Angeles, California 90095, USA
| | - Walter Gekelman
- Department of Physics and Astronomy, University of California, Los Angeles, Los Angeles, California 90095, USA
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