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1
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Ghazaryan S, Kaloyan M, Gekelman W, Lucky Z, Vincena S, Tripathi SKP, Pribyl P, Niemann C. Thomson scattering on the large plasma device. Rev Sci Instrum 2022; 93:083514. [PMID: 36050046 DOI: 10.1063/5.0099172] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2022] [Accepted: 07/18/2022] [Indexed: 06/15/2023]
Abstract
We have developed a non-collective Thomson scattering diagnostic for measurements of electron density and temperature on the Large Plasma Device. A triple grating spectrometer with a tunable notch filter is used to discriminate the faint scattering signal from the stray light. In this paper, we describe the diagnostic and its calibration via Raman scattering and present the first measurements performed with the fully commissioned system. Depending on the discharge conditions, the measured densities and temperatures range from 4.0 × 1012 to 2.8 × 1013 cm-3 and from 1.2 to 6.8 eV, respectively. The variation of the measurement error with plasma parameters and discharges averaged is also discussed.
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Affiliation(s)
- S Ghazaryan
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, California 90095, USA
| | - M Kaloyan
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, California 90095, USA
| | - W Gekelman
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, California 90095, USA
| | - Z Lucky
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, California 90095, USA
| | - S Vincena
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, California 90095, USA
| | - S K P Tripathi
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, California 90095, USA
| | - P Pribyl
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, California 90095, USA
| | - C Niemann
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, California 90095, USA
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2
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Gekelman W, Tang SW, DeHaas T, Vincena S, Pribyl P, Sydora R. Spiky electric and magnetic field structures in flux rope experiments. Proc Natl Acad Sci U S A 2019; 116:18239-18244. [PMID: 29925603 PMCID: PMC6744923 DOI: 10.1073/pnas.1721343115] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Magnetic flux ropes are structures that are common in the corona of the sun and presumably all stars. They can be thought of as the building blocks of solar structures. They have been observed in Earth's magnetotail and near Mars and Venus. When multiple flux ropes are present magnetic field line reconnection, which converts magnetic energy to other forms, can occur when they collide. The structure of multiple magnetic ropes, the interactions between multiple ropes, and their topological properties such as helicity and writhing have been studied theoretically and in laboratory experiments. Here, we report on spiky potential and magnetic fields associated with the ropes. We show that the potential structures are chaotic for a range of their temporal half-widths and the probability density function (PDF) of their widths resembles the statistical distribution of crumpled paper. The spatial structure of the magnetic spikes is revealed using a correlation counting method. Computer simulation suggests that the potential structures are the nonlinear end result of an instability involving relative drift between ions and electrons.
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Affiliation(s)
- W Gekelman
- Department of Physics and Astronomy, University of California, Los Angeles, CA 90095;
| | - S W Tang
- Department of Physics and Astronomy, University of California, Los Angeles, CA 90095
| | - T DeHaas
- Department of Physics and Astronomy, University of California, Los Angeles, CA 90095
| | - S Vincena
- Department of Physics and Astronomy, University of California, Los Angeles, CA 90095
| | - P Pribyl
- Department of Physics and Astronomy, University of California, Los Angeles, CA 90095
| | - R Sydora
- Department of Physics, University of Alberta, Edmonton, AB, Canada T6G 2R3
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3
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Gekelman W, Pribyl P, Vincena S, Tang SW, Papadopoulos K. Ferrite based antennae for launching Alfvén waves. Rev Sci Instrum 2019; 90:083505. [PMID: 31472640 DOI: 10.1063/1.5103171] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2019] [Accepted: 08/01/2019] [Indexed: 06/10/2023]
Abstract
Whistler and Alfvén waves are known to scatter mirror-trapped electrons and protons into the loss cone of the earth's dipole magnetic field. An array of satellites with properly phased antennas can be used to artificially reduce the flux of energetic particles from regions where their flux has been naturally or artificially pumped. In any space based system, the power required to drive antennas is at a premium. We present here experimental evidence that the efficiency of an antenna can be greatly enhanced with the use of ferrite cores with high relative magnetic permeability μ. Ferrite-based antennas were constructed to launch Alfvén waves in a magnetized plasma. The wave magnetic field of shear Alfvén waves launched with a ferrite core was by the magnetization factor μ larger than that of a similar antenna without a ferrite. Combining multiple ferrite antennas allowed control of the injected perpendicular wavelength. This novel technique can be used to efficiently launch low frequency waves with amplitude above the threshold required for nonlinear triggering.
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Affiliation(s)
- W Gekelman
- 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
| | - S Vincena
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - S W Tang
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - K Papadopoulos
- Departments of Physics and Astronomy, University of Maryland, College Park, Maryland 20742, USA
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4
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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. Phys Rev Lett 2017; 119:205002. [PMID: 29219335 DOI: 10.1103/physrevlett.119.205002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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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5
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Van Compernolle B, An X, Bortnik J, Thorne RM, Pribyl P, Gekelman W. Erratum: Excitation of Chirping Whistler Waves in a Laboratory Plasma [Phys. Rev. Lett. 114, 245002 (2015)]. Phys Rev Lett 2016; 117:059901. [PMID: 27517795 DOI: 10.1103/physrevlett.117.059901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2016] [Indexed: 06/06/2023]
Abstract
This corrects the article DOI: 10.1103/PhysRevLett.114.245002.
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6
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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. Phys Rev Lett 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] [What about the content of this article? (0)] [Affiliation(s)] [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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7
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Wang Y, Pribyl P, Gekelman W. A megawatt solid-state modulator for high repetition rate pulse generation. Rev Sci Instrum 2016; 87:023509. [PMID: 26931851 DOI: 10.1063/1.4941678] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2015] [Accepted: 01/24/2016] [Indexed: 06/05/2023]
Abstract
A novel solid-state modulator capable of generating rapid consecutive power pulses is constructed to facilitate experiments on plasma interaction with high power microwave pulses. The modulator is designed to output a 100 kHz tone burst, which consists of up to 10 pulses, each with 1 μs duration and 1 MW peak power. The pulses are formed by discharging a total of 480 μF capacitors through 24 synchronized MOSFETs and 6 step-up transformers. The highly modular design, as a replacement of an old single-pulse version used in earlier experiments which employs a pulse forming network, brings great flexibility and wide potential to its application. A systematic cost-effectiveness analysis is also presented.
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Affiliation(s)
- Y Wang
- 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
| | - W Gekelman
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
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8
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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. Rev Sci Instrum 2016; 87:025105. [PMID: 26931889 DOI: 10.1063/1.4941079] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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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9
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Abstract
The plasma potential, V(p), is a key quantity in experimental plasma physics. Its spatial gradients directly yield the electrostatic field present. Emissive probes operating under space-charge limited emission conditions float close to V(p) even under time-varying conditions. Throughout their long history in plasma physics, they have mostly been constructed with resistively heated tungsten wire filaments. In high density plasmas (>10(12) cm(-3)), hexaboride emitters are required because tungsten filaments cannot be heated to sufficient emission without component failure. A resistively heated emissive probe with a cerium hexaboride, CeB6, emitter has been developed to work in plasma densities up to 10(13) cm(-3). To show functionality, three spatial profiles of V(p) are compared using the emissive probe, a cold floating probe, and a swept probe inside a plasma containing regions with and without current. The swept probe and emissive probe agree well across the profile while the floating cold probe fails in the current carrying region.
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Affiliation(s)
- M J Martin
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - J Bonde
- 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
| | - P Pribyl
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
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10
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Tripathi SKP, Van Compernolle B, Gekelman W, Pribyl P, Heidbrink W. Excitation of shear Alfvén waves by a spiraling ion beam in a large magnetoplasma. Phys Rev E Stat Nonlin Soft Matter Phys 2015; 91:013109. [PMID: 25679725 DOI: 10.1103/physreve.91.013109] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2014] [Indexed: 06/04/2023]
Abstract
Generation of shear Alfvén waves by the Doppler-shifted ion-cyclotron-resonance (DICR) of a spiraling H(+) ion beam with magnetic fluctuations in a dual-species magnetized plasma with He(+) and H(+) ions has been investigated on the Large Plasma Device. The ambient plasma density and electron temperature were significantly enhanced by the beam. The Alfvén waves were left-handed polarized and traveled in the direction opposite to the ion beam. This is the first experimental demonstration of the DICR excitation of traveling shear Alfvén waves in a laboratory magnetoplasma.
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Affiliation(s)
- S K P Tripathi
- Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90095
| | - B Van Compernolle
- Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90095
| | - W Gekelman
- Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90095
| | - P Pribyl
- Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90095
| | - W Heidbrink
- Physics and Astronomy, University of California at Irvine, Irvine, California 92697
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11
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Van Compernolle B, Bortnik J, Pribyl P, Gekelman W, Nakamoto M, Tao X, Thorne RM. Direct detection of resonant electron pitch angle scattering by whistler waves in a laboratory plasma. Phys Rev Lett 2014; 112:145006. [PMID: 24765981 DOI: 10.1103/physrevlett.112.145006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2013] [Indexed: 06/03/2023]
Abstract
Resonant interactions between energetic electrons and whistler mode waves are an essential ingredient in the space environment, and in particular in controlling the dynamic variability of Earth's natural radiation belts, which is a topic of extreme interest at the moment. Although the theory describing resonant wave-particle interaction has been present for several decades, it has not been hitherto tested in a controlled laboratory setting. In the present Letter we report on the first laboratory experiment to directly detect resonant pitch angle scattering of energetic (∼keV) electrons due to whistler mode waves. We show that the whistler mode wave deflects energetic electrons at precisely the predicted resonant energy, and that varying both the maximum beam energy, and the wave frequency, alters the energetic electron beam very close to the resonant energy.
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Affiliation(s)
- B Van Compernolle
- Department of Physics, University of California, Los Angeles, California 90095, USA
| | - J Bortnik
- Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California 90095, USA
| | - P Pribyl
- Department of Physics, University of California, Los Angeles, California 90095, USA
| | - W Gekelman
- Department of Physics, University of California, Los Angeles, California 90095, USA
| | - M Nakamoto
- Department of Physics, University of California, Los Angeles, California 90095, USA
| | - X Tao
- Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California 90095, USA
| | - R M Thorne
- Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California 90095, USA
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12
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Cooper CM, Gekelman W. Termination of a magnetized plasma on a neutral gas: the end of the plasma. Phys Rev Lett 2013; 110:265001. [PMID: 23848883 DOI: 10.1103/physrevlett.110.265001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2013] [Indexed: 06/02/2023]
Abstract
Experiments are performed at the Enormous Toroidal Plasma Device at UCLA to study the neutral boundary layer (NBL) between a magnetized plasma and a neutral gas along the direction of a confining magnetic field. This is the first experiment to measure plasma termination within a neutral gas without the presence of a wall or obstacle. A magnetized, current-free helium plasma created by a lanthanum hexaboride (LaB6) cathode terminates entirely within a neutral helium gas. The plasma is weakly ionized (ne/nn∼1%) and collisional λn≪Lplasma}. The NBL occurs where the plasma pressure equilibrates with the neutral gas pressure, consistent with a pressure balance model. It is characterized by a field-aligned ambipolar electric field, developing self-consistently to maintain a current-free termination of the plasma on the neutral gas. Probes are inserted into the plasma to measure the plasma density, flow, temperature, current, and potential. These measurements confirm the presence of the ambipolar field and the pressure equilibration model of the NBL.
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Affiliation(s)
- C M Cooper
- University of California, Los Angeles, Los Angeles, California 90024, USA
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13
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Wang Y, Gekelman W, Pribyl P. Hard x-ray tomographic studies of the destruction of an energetic electron ring. Rev Sci Instrum 2013; 84:053503. [PMID: 23742547 DOI: 10.1063/1.4804354] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
A tomography system was designed and built at the Large Plasma Device to measure the spatial distribution of hard x-ray (100 KeV-3 MeV) emissivity. The x-rays were generated when a hot electron ring was significantly disrupted by a shear Alfvén wave. The plasma is pulsed at 1 Hz (1 shot/s). A lead shielded scintillator detector with an acceptance angle defined by a lead pinhole is mounted on a rotary gimbal and used to detect the x-rays. The system measures one chord per plasma shot using only one detector. A data plane usually consists of several hundred chords. A novel Dot by Dot Reconstruction (DDR) method is introduced to calculate the emissivity profile from the line integrated data. In the experiments, there are often physical obstructions, which make measurements at certain angles impossible. The DDR method works well even in this situation. The method was tested with simulated data, and was found to be more effective than previously published methods for the specific geometry of this experiment. The reconstructed x-ray emissivity from experimental data by this method is shown.
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Affiliation(s)
- Y Wang
- Department of Physics and Astronomy, University of California-Los Angeles, Los Angeles, California 90095, USA
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14
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Tripathi SKP, Pribyl P, Gekelman W. Development of a radio-frequency ion beam source for fast-ion studies on the large plasma device. Rev Sci Instrum 2011; 82:093501. [PMID: 21974581 DOI: 10.1063/1.3631628] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
A helium ion beam source (23 kV/2.0 A) has been constructed for studying fast-ion physics in the cylindrical magnetized plasma of the large plasma device (LAPD). An inductive RF source produces a 10(19) m(-3) density plasma in a ceramic dome. A multi-aperture, rectangular (8 cm × 8 cm) three-grid system extracts the ion beam from the RF plasma. The ion beam is injected at a variety of pitch angles with Alfvénic speeds in the LAPD. The beam current is intense enough to excite magnetic perturbations in the ambient plasma. Measurements of the ion beam profile were made to achieve an optimum beam performance and a reliable source operation was demonstrated on the LAPD.
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Affiliation(s)
- S K P Tripathi
- Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90095, USA
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15
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Abstract
We describe the first-ever volumetric, time-resolved measurements performed with a moving probe within an expanding dense plasma, embedded in a background magnetized plasma. High-resolution probe measurements of the magnetic field and floating potential in multiple 2D cut planes combined with a 1 Hz laser system reveal complex three-dimensional current systems within the expanding plasma. Static (ωreal=0) flutelike density striations are observed at the leading edge of the plasma, which are correlated to variations in the current layer at the edge of the expanding plasma.
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Affiliation(s)
- A Collette
- Department of Physics and Astronomy, University of California, Los Angeles, Los Angeles, California 90095, USA.
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16
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Tripathi SKP, Gekelman W. Laboratory simulation of arched magnetic flux rope eruptions in the solar atmosphere. Phys Rev Lett 2010; 105:075005. [PMID: 20868055 DOI: 10.1103/physrevlett.105.075005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2010] [Indexed: 05/29/2023]
Abstract
Dramatic eruption of an arched magnetic flux rope in a large ambient plasma has been studied in a laboratory experiment that simulates coronal loops. The eruption is initiated by laser generated plasma flows from the footpoints of the rope that significantly modify the magnetic-field topology and link the magnetic-field lines of the rope with the ambient plasma. Following this event, the flux rope erupts by releasing its plasma into the background. The resulting impulse excites intense magnetosonic waves that transfer energy to the ambient plasma and subsequently decay.
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Affiliation(s)
- S K P Tripathi
- Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90095, USA.
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17
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Abstract
A new 18x18 cm(2) active area lanthanum hexaboride (LaB(6)) plasma source for use in a dc discharge has been developed at UCLA. The cathode consists of four tiled LaB(6) pieces indirectly heated to electron emission (1750 degrees C) by a graphite heater. A molybdenum mesh anode 33 cm in front of the LaB(6) accelerates the electrons, ionizing a fill gas to create a 20x20 cm(2) nearly square plasma. The source is run in pulsed operation with the anode biased up to +400 V dc with respect to the cathode for up to 100 ms at a 1 Hz repetition rate. Both the cathode and anode "float" electrically with respect to the chamber walls. The source is placed in a toroidal chamber 2 m wide and 3 m tall with a major radius of 5 m. Toroidal and vertical magnetic fields confine the current-free plasma which follows the field in a helix. The plasma starts on the bottom of the machine and spirals around it up to four times (120 m) and can be configured to terminate either on the top wall or on the neutral gas itself. The source typically operates with a discharge current up to 250 A in helium making plasmas with T(e)<30 eV, T(i)<16 eV, and n(e)<3x10(13) cm(-3) in a background field of 100 G<B(o)<320 G, giving a magnetized plasma with 0.1<beta<1.
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Affiliation(s)
- C M Cooper
- University of California, Los Angeles, California 90095, USA
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18
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Gekelman W, Barnes M, Vincena S, Pribyl P. Correlation analysis of waves above a capacitive plasma applicator. Phys Rev Lett 2009; 103:045003. [PMID: 19659363 DOI: 10.1103/physrevlett.103.045003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2009] [Indexed: 05/28/2023]
Abstract
Capacitively coupled plasma glow discharges have been extensively used for materials processing in numerous industrial applications. Considerable research has been performed on plasma sheaths and standing waves over a capacitive applicator, which typically holds the processed substrate (e.g., a semiconductor wafer). In this work, we demonstrate for the first time the existence of normal modes in electric potential analogous to the vibrational modes in circular membranes and plates. These modes are exhibited through cross spectral analysis of the plasma potential measured with an emissive probe at 208 spatial positions and sampled at 1 GHz. These modes exist at several frequencies and are described by a series of Bessel functions. The data further suggests a nonlinear interaction between modes of different frequencies.
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Affiliation(s)
- W Gekelman
- Department of Physics and Astronomy, University of California, Los Angeles, California, USA
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Collette A, Gekelman W. Two-dimensional micron-step probe drive for laboratory plasma measurement. Rev Sci Instrum 2008; 79:083505. [PMID: 19044347 DOI: 10.1063/1.2972150] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Laboratory measurement of small-scale ( approximately 1 mm) magnetic phenomena over an extended area is a challenge requiring precise diagnostics. We present a novel two dimensional magnetic probe platform capable of directly measuring the magnetic field over a 36 cm(2) region at spatial resolutions better than 1 mm. The platform is discussed in the context of an experiment at the Large Plasma Device facility at UCLA, designed to measure the magnetic interaction between two counterpropagating laser-produced plasmas. The use of a precise, repeatable positioning platform enables the recovery of information about the interaction using cross-correlation techniques.
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Affiliation(s)
- A Collette
- Department of Physics and Astronomy, University of California, Los Angeles, 1000 Veteran Ave., Suite 15-70, California 90095, USA
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Kletzing CA, Bounds SR, Martin-Hiner J, Gekelman W, Mitchell C. Measurements of the shear Alfvén wave dispersion for finite perpendicular wave number. Phys Rev Lett 2003; 90:035004. [PMID: 12570497 DOI: 10.1103/physrevlett.90.035004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2001] [Revised: 06/19/2002] [Indexed: 05/24/2023]
Abstract
Measurements of the dispersion relation for shear Alfvén waves as a function of the perpendicular wave number are reported for the regime in which V(A) approximately V(Te). By measuring the parallel phase velocity of the waves, the measurements can be compared directly to theoretical predictions of the dispersion relation for a parameter regime in which particle kinetic effects become important. The comparison shows that the best agreement between theory and experiment is achieved when a fully complex, warm plasma dispersion relation is used.
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Affiliation(s)
- C A Kletzing
- Department of Physics and Astronomy, University of Iowa, 203 Van Allen Hall, Iowa City, Iowa 52245, USA.
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VanZeeland M, Gekelman W, Vincena S, Dimonte G. Production of Alfvén waves by a rapidly expanding dense plasma. Phys Rev Lett 2001; 87:105001. [PMID: 11531482 DOI: 10.1103/physrevlett.87.105001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2001] [Indexed: 05/23/2023]
Abstract
The expansion of a dense (initially, n(lpp)/n(0)>>1) laser-produced plasma into an ambient magnetized plasma ( n(0) = 2 x 10(12) cm(-3)) capable of supporting Alfvén waves has been studied. The interaction results in the production of shear Alfvén waves as well as large density perturbations (Delta n/n(0) approximately 0.3) associated with the moving dense plasma. The waves propagate away from the target and are observed to become plasma-column resonances. Spatial patterns of the wave magnetic fields are measured and are used to estimate the coupling efficiency of the laser energy and the kinetic energy of the dense plasma into wave energy.
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Affiliation(s)
- M VanZeeland
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
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Bamber JF, Maggs JE, Gekelman W. Whistler wave interaction with a density striation: A laboratory investigation of an auroral process. ACTA ACUST UNITED AC 1995. [DOI: 10.1029/95ja01852] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Bamber JF, Gekelman W, Maggs JE. Whistler wave mode conversion to lower hybrid waves at a density striation. Phys Rev Lett 1994; 73:2990-2993. [PMID: 10057254 DOI: 10.1103/physrevlett.73.2990] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Gekelman W, Pfister H, Kan JR. Experimental observations of patchy reconnections associated with the three-dimensional tearing instability. ACTA ACUST UNITED AC 1991. [DOI: 10.1029/90ja02630] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Gekelman W, Stenzel RL. Measurement and instability analysis of three-dimensional anisotropic electron distribution functions. Phys Rev Lett 1985; 54:2414-2417. [PMID: 10031336 DOI: 10.1103/physrevlett.54.2414] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Gekelman W, Stenzel RL, Wild N. Magnetic field line reconnection experiments, 3. Ion acceleration, flows, and anomalous scattering. ACTA ACUST UNITED AC 1982. [DOI: 10.1029/ja087ia01p00101] [Citation(s) in RCA: 62] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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