This research investigates the electrical resistivity of a plasma during the collision of magnetic flux ropes, which are common structures in astrophysical plasmas. The researchers performed laboratory experiments using the Large Plasma Device (LaPD) at UCLA, measuring the magnetic field, plasma potential, plasma flow, temperature, and density at various spatial locations. They found that the traditional Ohm's Law (describing resistivity) could not be used to calculate the resistivity due to non-local effects. Instead, they used the Kubo conductivity formula, which is derived from the fluctuation-dissipation theorem, to determine the global resistivity. The results indicate that the resistivity is enhanced in regions where the magnetic field lines reconnect and the current density is large, suggesting that the process is related to the scattering of electrons by waves or turbulence in the plasma.

Basic Plasma Science Facility: https://plasma.physics.ucla.edu

Article being discussed: W. Gekelman, T. DeHaas, P. Pribyl, S. Vincena, B. Van Compernolle, R. Sydora, and S. K. P. Tripathi, "Nonlocal Ohm's Law, Plasma Resistivity, and Reconnection During Collisions of Magnetic Flux Ropes," ApJ 853 33, (2018); https://doi.org/10.3847/1538-4357/aa9fec

The Basic Plasma Science Facility is a Collaborative Research Facility that is primarily funded by the US Department of Energy Fusion Energy Sciences program, with additional funding from the National Science Foundation.

Our hosts discuss a paper that reports on an experiment using the Large Plasma Device (LAPD) to study the effects of magnetic reconnection on ions. The experiment used two kink-unstable flux ropes, which are current-carrying columns of plasma that collide and cause magnetic reconnection. Magnetic reconnection is a process that converts stored magnetic energy into particle energy. The experiment observed a field-aligned ion beam with energies up to 15 eV that was correlated with the collision of the ropes and was not heated. The study was supported by 3D gyrokinetic particle simulations which demonstrated that the ion acceleration was caused by a combination of inductive and space charge electric fields, resulting in a non-local acceleration of ions. The authors claim that this is the first experimental observation of a field-aligned ion beam produced by magnetic reconnection.

Basic Plasma Science Facility: https://plasma.physics.ucla.edu

Article being discussed: S. W. Tang, W. Gekelman, and R. D. Sydora, "Experimental observation of a field-aligned ion beam produced by magnetic reconnection of two flux ropes," Phys. Plasmas 30, 082104 (2023); https://doi.org/10.1063/5.0138350

The Basic Plasma Science Facility is a Collaborative Research Facility that is primarily funded by the US Department of Energy Fusion Energy Sciences program, with additional funding from the National Science Foundation.

This research article details a laboratory experiment designed to model the eruptive behavior of arched magnetized plasmas, such as those found in the Sun's atmosphere. The researchers created an arched plasma in a vacuum chamber and subjected it to a magnetic field, mimicking the conditions of the solar photosphere and lower chromosphere. They observed the formation of a transient plasma jet, similar to solar jets and spicules, driven by magnetic shear and large pressure gradients. The jet's supersonic flow and complex electric current structure were studied in detail, with particular focus on the role of ion-neutral collisions in shaping the jet's dynamics. The results provide insights into the mechanisms behind solar eruptions and the behavior of magnetized plasmas in astrophysical environments.

Basic Plasma Science Facility: https://plasma.physics.ucla.edu

Article being discussed: Kamil D. Sklodowski, Shreekrishna Tripathi, and Troy Carter, "Dynamic Formation of a Transient Jet from Arched Magnetized Laboratory Plasma," the Astrophysical Journal, Volume 953, Number 1, 2023; https://doi.org/10.3847/1538-4357/acdf47

The Basic Plasma Science Facility is a Collaborative Research Facility that is primarily funded by the US Department of Energy Fusion Energy Sciences program, with additional funding from the National Science Foundation.

This scientific article reports the first experimental detection of reflected Alfvén waves from an Alfvén-speed gradient in a laboratory setting, mimicking conditions found in coronal holes on the Sun. The study, conducted in the Large Plasma Device (LAPD) at the University of California, Los Angeles, focused on the impact of Alfvén-speed inhomogeneity on Alfvén wave reflection. The researchers varied the Alfvén-speed gradient and the wavelength of the incident Alfvén wave to study the resulting reflection. The experimental findings were supported by simulations using the Gkeyll code, showing a strong correlation between the strength of the Alfvén-speed gradient and the amount of wave reflection. The research suggests that wave reflection from smooth Alfvén-speed gradients in coronal holes may contribute significantly to the heating of the solar corona, particularly at lower heights, through the process of wave-driven turbulence.

Basic Plasma Science Facility: https://plasma.physics.ucla.edu

Article being discussed: Sayak Bose, Jason M. TenBarge, Troy Carter, Michael Hahn, Hantao Ji, James Juno, Daniel Wolf Savin, Shreekrishna Tripathi, and Stephen Vincena, “Experimental Study of Alfvén Wave Reflection from an Alfvén-speed Gradient Relevant to the Solar Coronal Holes”, The Astrophysical Journal, 971:72, 12pp, (2024); https://dx.doi.org/10.3847/1538-4357/ad528f

The Gkeyll 2.0 simulation code: https://gkeyll.readthedocs.io/en/latest/

The Basic Plasma Science Facility is a Collaborative Research Facility that is primarily funded by the US Department of Energy Fusion Energy Sciences program, with additional funding from the National Science Foundation.

The scientific paper, "Laboratory Study of Magnetic Reconnection in Lunar-relevant Mini-magnetospheres", reports on an experiment that simulated the interaction between the solar wind and the Moon's mini-magnetospheres. The authors created a mini-magnetosphere in the laboratory using a laser-driven plasma, and they observed magnetic reconnection, a fundamental process in space plasmas. The researchers found that the reconnection was driven by kinetic effects, through what is known as the electron pressure anisotropy. They also observed Hall fields, which are electric fields created by the difference in motion between ions and electrons. By comparing their experimental results to satellite data and computer simulations, they concluded that the reconnection process observed in the laboratory is relevant to what happens in lunar mini-magnetospheres.

Basic Plasma Science Facility: https://plasma.physics.ucla.edu

Article being discussed: Lucas Rovige, Filipe D. Cruz, Robert S. Dorst, Jessica J. Pilgram, Carmen G. Constantin, Stephen Vincena, Fábio Cruz, Luis O. Silva, Christoph Niemann, and Derek B. Schaeffer, “Laboratory Study of Magnetic Reconnection in Lunar-relevant Mini-magnetospheres,” The Astrophysical Journal 969:124, 8pp, (2024); https://doi.org/10.3847/1538-4357/ad4fff

The Basic Plasma Science Facility is a Collaborative Research Facility that is primarily funded by the US Department of Energy Fusion Energy Sciences program, with additional funding from the National Science Foundation.

This research paper presents the results of experiments and simulations investigating the nonlinear interaction between spinning magnetized plasma pressure filaments. The experiments, conducted in a large linear magnetized plasma device, used controlled, skin depth-sized plasma pressure filaments in close proximity to observe how they interacted. The researchers found that when the filaments were separated by a distance of approximately five times the size of a single filament or less, a significant transfer of charge and energy occurred, leading to the generation of inter-filament electric fields. This resulted in the rotation of the filaments and influenced their merging dynamics. These results were confirmed by nonlinear gyrokinetic simulations, which revealed unstable drift-Alfvén modes driven by the steep electron temperature gradient. The study also explored the impact of filament separation on the mode structure and found that closer filaments resulted in more complex mode patterns. The insights gained from this study have implications for understanding the dynamics of plasma filaments in various environments, including fusion reactors and space plasmas.

URLS:

Basic Plasma Science Facility: https://plasma.physics.ucla.edu

Article being discussed: R. D. Sydora, T. Simala-Grant, S. Karbashewski, F. Jimenez, B. Van Compernolle, M. J. Poulos; Experiments and gyrokinetic simulations of the nonlinear interaction between spinning magnetized plasma pressure filaments. Phys. Plasmas 1 August 2024; 31 (8): 082304. https://doi.org/10.1063/5.0213345

The Basic Plasma Science Facility is a Collaborative Research Facility that is primarily funded by the US Department of Energy Fusion Energy Sciences program, with additional funding from the National Science Foundation.

This study investigates the motion and energy distribution of argon ions in a plasma etching reactor. The researchers utilized laser-induced fluorescence (LIF) to measure the ions' velocity and energy distribution in the presence of an RF bias on a silicon wafer. They explored various conditions, including pulsed operation of the inductively coupled plasma (ICP) and the bias, as well as the impact of applying the bias during the plasma afterglow. These findings were then compared to simulations using the Hybrid Plasma Equipment Model (HPEM) code. The study demonstrates the potential for improving etch uniformity by pulsing the ICP and bias independently, particularly when applying the bias during the afterglow.

URLS:

Basic Plasma Science Facility: https://plasma.physics.ucla.edu

Article being discussed: Yuchen Qian, Walter Gekelman, Patrick Pribyl, Tugba Piskin, Alex Paterson; Ion motion above a biased wafer in a plasma etching reactor. Phys. Plasmas 1 June 2024; 31 (6): 063507. https://doi.org/10.1063/5.0206860

The Basic Plasma Science Facility is a Collaborative Research Facility that is primarily funded by the US Department of Energy Fusion Energy Sciences program, with additional funding from the National Science Foundation.

This study presents an experimental observation of a three-wave coupling between a shear Alfvén wave and a kink-unstable magnetic flux rope in a laboratory setting. By launching an Alfvén wave in a current-carrying plasma column, researchers observed the emergence of sidebands in the frequency power spectrum of the Alfvén wave, spaced by integer multiples of the kink frequency. The researchers demonstrate that these sidebands satisfy both frequency and wavenumber matching conditions for three-wave interactions. Bispectral analysis reveals a significant quadratic nonlinear interaction between the kink and Alfvén waves, which drives the generation of the sidebands. This study highlights the importance of nonlinear wave-wave interactions in plasmas, particularly in understanding energy transport and heating mechanisms in astrophysical and laboratory settings.

URLS:

Basic Plasma Science Facility: https://plasma.physics.ucla.edu

Article being discussed: https://doi.org/10.1063/5.0217895

S. Vincena, S. K. P. Tripathi, W. Gekelman, P. Pribyl; Three-wave coupling observed between a shear Alfvén wave and a kink-unstable magnetic flux rope. Phys. Plasmas 1 September 2024; 31 (9): 092302.