Laboratory study of collisionless coupling between explosive debris plasma and magnetized ambient plasma
Abstract
The explosive expansion of a localized plasma cloud into a relatively tenuous, magnetized, ambient plasma characterizes a variety of astrophysical and space phenomena. In these rarified environments, collisionless electromagnetic processes rather than Coulomb collisions typically mediate the transfer of momentum and energy from the expanding “debris” plasma to the surrounding ambient plasma. In an effort to better understand the detailed physics of collisionless coupling mechanisms, compliment in situ measurements of space phenomena, and provide validation of previous computational and theoretical work, the present research jointly utilizes the Large Plasma Device and the Raptor laser facility at the University of California, Los Angeles to study the super-Alfvénic, quasi-perpendicular expansion of laser-produced carbon (C) and hydrogen (H) debris plasma through preformed, magnetized helium (He) ambient plasma via a variety of diagnostics, including emission spectroscopy, wavelength-filtered imaging, and a magnetic flux probe. Doppler shifts detected in a He1+ ion spectral line indicate that the ambient ions initially accelerate transverse to both the debris plasma flow and the background magnetic field. A qualitative analysis in the framework of a “hybrid” plasma model (kinetic ions and inertia-less fluid electrons) demonstrates that the ambient ion trajectories are consistent with the large-scale laminar electric field expected to develop due to the expanding debris. In particular, the transverse ambient ion motion provides direct evidence of Larmor coupling, a collisionless momentum exchange mechanism that has received extensive theoretical and numerical investigation. In order to quantitatively evaluate the observed Doppler shifts, a custom simulation utilizing a detailed model of the laser-produced debris plasma evolution calculates the laminar electric field and computes the initial response of a distribution of ambient test ions. A synthetic Doppler-shifted spectrum constructed from the simulated test ion velocities excellently reproduces the experimental measurements, verifying that the observed ambient ion motion corresponds to collisionless coupling through the laminar electric field.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Aug 01, 2017
- Source ID
- 10.1063/1.4995480
Entities
People
- A. S. Bondarenko
- B. R. Lee
- Bart Van Compernolle
- C. G. Constantin
- Christoph Niemann
- D. Winske
- Derek Schaeffer
- E. T. Everson
- S. E. Clark
- Shreekrishna Tripathi
- Stephen Vincena
Organizations
- Defense Threat Reduction Agency
- German Research Foundation
- Los Alamos National Laboratory
- National Science Foundation
- Technical University of Darmstadt
- United States Department of Energy
- University of California, Los Angeles