Three-dimensional MHD Simulation of the Caltech Plasma Jet Experiment: First Results
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 simulations of 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.
© 2014 The American Astronomical Society. Received 2013 December 9; Accepted 2014 June 22; Published 2014 July 24. The experimental program at Caltech is supported by the NSF/DOE Partnership in Plasma Science. H.L. is grateful to Stirling Colgate, Ken Fowler, and Ellen Zweibel for discussions. H.L. and S.L. are supported by the LANL/LDRD and Institutional Computing Programs at LANL and by DOE/Office of Fusion Energy Science through CMSO.
Published - 0004-637X_791_1_40.pdf
Accepted Version - 1407.3498v1.pdf