Development of a polarization resolved spectroscopic diagnostic for measurements of the vector magnetic field in the Caltech coaxial magnetized plasma jet experiment

Shikama, T.; Bellan, Paul M.

doi:10.1063/1.4793403

Cited by 7 publications

(6 citation statements)

References 24 publications

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“…If, for example, the ionization fraction were α = 10 −12 , the cyclotron frequency of the metaparticle represented by the clump would be 12 orders of magnitude smaller than that of an ion and so could easily become comparable to a Kepler frequency. This α −1 -fold reduction of effective ion cyclotron frequency in a weakly ionized plasma has been previously noted in other contexts by Song, Vasyliunas & Ma (2005) and by Pandey & Wardle (2008).…”

Section: Accretion Disk Launching Of Jetssupporting

confidence: 80%

“…In contrast, it is possible in the Caltech experiment to scan parameters or move a probe over many shots to establish an experimentally measured scaling or an experimentally determined spatial profile. The time-dependent interior magnetic field profile of the Caltech experiment has been measured directly by magnetic probes and these measurements have been confirmed by spectroscopic measurement of Zeeman line splitting (Shikama & Bellan 2013). The interior magnetic field profile in the Imperial College experiment has been estimated using comparisons with computer models; a single-point magnetic probe measurement has been made but the calibration was uncertain (Suzuki-Vidal et al 2014).…”

Section: Discussionmentioning

confidence: 99%

“…The temperature is much less variable and is typically 2–4 eV. Shikama & Bellan (2013) made detailed spectroscopic measurements near the electrodes in a nitrogen plasma. These measurements indicated a peak density of using Stark broadening and a peak magnetic field using Zeeman splitting.…”

Section: Experimental Set-upmentioning

confidence: 99%

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Experiments relevant to astrophysical jets

Bellan

2018

J. Plasma Phys.

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This paper summarizes the results of an experimental program at Caltech wherein magnetohydrodynamically driven plasma jets are created and diagnosed. The theory modelling these jets, the main experimental results and their relevance to astrophysical jets are presented. The model explains how the jets are driven and why they self-collimate. Characteristic kink and Rayleigh–Taylor instabilities are shown to occur and the ramifications of these instabilities are discussed. Extending the experimental results to the astrophysical situation reveals a shortcoming in ideal magnetohydrodynamics (MHD) that must be remedied by replacing the ideal MHD Ohm’s law by the generalized Ohm’s law. It is shown that when the generalized Ohm’s law is used and the consequences of weak ionization are taken into account, an accretion disk behaves much like the electrodes, mass source and power supply used in the experiment.

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Section: Accretion Disk Launching Of Jetssupporting

confidence: 80%

Section: Discussionmentioning

confidence: 99%

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Experiments relevant to astrophysical jets

Bellan

2018

J. Plasma Phys.

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“…The poloidal magnetic field strength in the plasma is also amplified from < 0.05 T to ∼ 0.2 T, indicating that the field is frozen into the plasma and is collimated together with the plasma. This amplification of the magnetic field strength has also been observed spectroscopically (Shikama & Bellan 2013). The thermal pressure and axial magnetic field pressure B 2 z /(2µ 0 ) increase until they balance the radial Lorentz force and lead to a nearly constant jet radius of 2 − 5 cm (Fig.…”

Section: Caltech Plasma Jet Experimentssupporting

confidence: 58%

Three-Dimensional MHD Simulation of the Caltech Plasma Jet Experiment: First Results

Zhai

Bellan

et al. 2014

ApJ

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Magnetic fields are believed to play an essential role in astrophysical jets with observations suggesting the presence of helical magnetic fields. Here, we present three-dimensional (3D) ideal MHD simulationsof the Caltech plasma jet experiment using a magnetic tower scenario as the baseline model. Magnetic fields consist of an initially localized dipole-like poloidal component and a toroidal component that is continuously being injected into the domain. This flux injection mimics the poloidal currents driven by the anode-cathode voltage drop in the experiment. The injected toroidal field stretches the poloidal fields to large distances, while forming a collimated jet along with several other key features. Detailed comparisons between 3D MHD simulations and experimental measurements provide a comprehensive description of the interplay among magnetic force, pressure and flow effects. In particular, we delineate both the jet structure and the transition process that converts the injected magnetic energy to other forms. With suitably chosen parameters that are derived from experiments, the jet in the simulation agrees quantitatively with the experimental jet in terms of magnetic/kinetic/inertial energy, total poloidal current, voltage, jet radius, and jet propagation velocity. Specifically, the jet velocity in the simulation is proportional to the poloidal current divided by the square root of the jet density, in agreement with both the experiment and analytical theory. This work provides a new and quantitative method for relating experiments, numerical simulations and astrophysical observation, and demonstrates the possibility of using terrestrial laboratory experiments to study astrophysical jets.

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“…Here, we present an experimental determination of B θ throughout the magnetized plasma implosion, achieved using a noninvasive spectroscopic technique that provides a high sensitivity for the Zeeman effect [26]. This technique is based on the polarization properties of the Zeeman components for light emission viewed parallel to the B-field, as described in [27][28][29][30], and recently implemented for Z-pinch implosions [24]. These measurements showed that the application of an initial axial magnetic field (B z0 ) has a significant effect on the current distribution in the plasma: a large part of the current does not flow in the imploding plasma, rather it flows through a low-density plasma (LDP) residing at large radii (here, by "current distribution" we mean the partition of the total current between the flow in the imploding plasma and the LDP).…”

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confidence: 99%