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| recent_progress_on_the_caltech_plasma_jet_experiment.pdf | 2013-03-04 10:42:07 | Xiang Zhai |
Recent progresses on the Caltech plasma jet experiment
Author: Xiang Zhai
Requested Type: Poster Only
Submitted: 2012-12-04 13:17:54
Co-authors: H. Li, P. M. Bellan
Contact Info:
Caltech
1200 E California Blvd
Pasadena, CA 91125
USA
Abstract Text:
Recent experimental investigations on the Caltech jet experiment reveal that two different types of Rayleigh-Taylor secondary instabilities can occur at the boundary of kinked Argon plasma jets. One has ≈5cm axial wavelength and usually evolves to smaller scale kinks in 3-4 microseconds; the other has ≈2cm axial wavelength and leads to fast non-MHD scale magnetic reconnection in 1-2 microsecond [1].
We also present a 3D ideal MHD numerical simulation of the jet experiment. The 800x800x800 grid simulation uses the 3D adaptive mesh refinement code AMR3d previously developed by H. Li and S. Li (LANL) for simulating magnetically driven astrophysical jets. The simulation involves injection of toroidal magnetic flux continuously into the plasma thereby increasing the magnetic energy and helicity. In both the simulation and the experiment, the Lorentz force squeezes the plasma radially and lengthens it axially to form a jet. With a suitably chosen initial mass distribution and helicity injection rate, the jet in the simulation agrees quantitatively with the experimental jet in 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 the Bernoulli MHD theory for jets [2]. Imposition of a small non-axisymmetric perturbation causes the jet in the simulation to kink, but so far this kinking is only qualitatively similar to the experimentally observed kink. Rayleigh-Taylor instability occurs only with an artificial external force applied perpendicular to the jet in the simulation; in contrast the Rayleigh-Taylor instability occurs spontaneously in the experiment.
[1]A. L. Moser and P. M. Bellan, Nature, 482, 379-381 (2012)
[2] D. Kumar and P. M. Bellan, Physical Review Letter, 103, 105003 (2009)
Characterization: 2.0,4.0
Comments:
