Laboratory Demonstration of Collisionless Blob Formation via Laser Produced Plasma Self-Focusing

ORAL  · Invited

Abstract

We observe the formation and propagation of an ion gryoradius scale blob-cavity structure at the interface between a super-Alfvénic laser produced plasma (LPP) and an ambient magnetized plasma as a result of Larmor coupling. The magnetic pressure gradients along the edge of the diamagnetic cavity focus the quasi-perpendicularly expanding LPP into a collimated flow that maintains late-time enhanced density compared to ballistic expansion. The Larmor electric fields generated in this expansion act upon the ambient plasma, driving an E × B motion of the ion and electron populations. This E × B drift results in a pile-up of the ambient ions resulting in a "blob". A secondary, miniature diamagnetic cavity is maintained between the collimated LPP and the blob and separates a relatively large distance from the bulk diamagnetic cavity. Three-dimensional particle-in-cell simulations replicating the experimental conditions reproduce the density increase of the ambient ions and reveal the individual mechanisms that lead to both the self-focusing of the LPP flow and creation of the blob-mini cavity structure. In these studies a novel, collisionless mechanism for blob production has been demonstrated that can help uncover dynamics involved in blobs observed during cometary transits and ionospheric disturbance.

*This work was supported by the Defense Threat Reduction Agency and Lawrence Livermore National Security LLC under contract numbers B643014, B649519, and B661613. Theexperiments were performed at the UCLA Basic Plasma Science Facility (BaPSF), which is a collaborative research facility supported by the U. S. Department of Energy, Office ofScience, Fusion Energy Sciences program, and the National Science Foundation.

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Presenters

  • Robert S Dorst

    • University of California, Los Angeles

Authors

  • Robert S Dorst

    • University of California, Los Angeles

  • Ari Le

    • Los Alamos National Laboratory

  • Carmen G Constantin

    • University of California, Los Angeles

  • David Jeffrey Larson

    • Lawrence Livermore Natl Lab

  • Steve T Vincena

    • UCLA
    • University of California, Los Angeles

  • Shreekrishna Tripathi

    • University of California, Los Angeles
    • Department of Physics and Astronomy, University of California, Los Angeles
    • UCLA

  • Misa Cowee

    • Los Alamos National Laboratory

  • Derek B Schaeffer

    • University of California, Los Angeles
    • UCLA

  • Christoph Niemann

    • University of California, Los Angeles