Seminars & Events

Generation of a magnetized collisionless shock and its study in a well-scaled laboratory setting

Dr. Bo Ram Lee (Technische Universität Darmstadt, Germany)

Dense plasma expansion into a tenuous magnetized background plasma is prevalent in space and astrophysical environments. In the interaction between plasmas with different densities under the influence of the magnetic field, various hydromagnetic waves are generated including the magnetized collisionless shocks which are believed to be the source of high energy particles, such as galactic cosmic rays from supernova remnants. Despite its importance in astrophysics and the study for longer than five decades, however, details of the shock physics, such as the formation process or the energy dissipation mechanisms are still not fully understood. In the present talk, the laser experiments carried out at the Large Plasma Device (LAPD) at University of California, Los Angeles (UCLA) are introduced. When a dense plasma produced by a laser (~200J) interacts with a preformed, magnetized background plasma (1013cm-3), a diamagnetic cavity is formed which can be pictured as a piston driving a magnetosonic pulse. When the conditions for shock formation are met, this pulse can become a collisionless shock (MA>2) and propagates through the ambient plasma. Recently, the first evidence for shock generation in the given experimental setting has been observed and the laminar electric fields which are created by the streaming of laser-plasma ions across the magnetic field and assumed to couple energy and momentum to the ambient ions in the absence of binary collisions between particles could be also detected. The collisionless coupling and the formation and structure of the shock that are measured with plasma probes as well as the features reproduced by the hybrid simulations similar to the experiment are presented.

Professional background
Since July 2016 Visiting researcher at KAIST – DAAD/NRF scholarship holder
(Prof. Hong Jin Kong, Laser Science Research Laboratory)
December 2015 Ph.D., Technische Universität Darmstadt, Germany
(Prof. Dieter H.H. Hoffmann, Plasma Physics Research Group)

Relevant publications
1) B.R. Lee et al., Collisionless interaction of a dense laser produced plasma with a large magnetized
low-density plasma (in preparation)
2) A. Bondarenko et al., Collisionless momentum transfer in space and astrophysical explosions
(submitted to Nature Physics)
3) D. Schaeffer et al., Experimental study of subcritical laboratory magnetized collisionless shocks
using a laser-driven magnetic piston. Physics of Plasmas (1994-present), 22(11):113101, 2015
4) B.R. Lee et al., Effect of electron pressure on debris-ambient coupling in a magnetized collisionless
shock, IEEE Transactions on Plasma Science , 43, 5, 1815-1819, 2015
5) D. Schaeffer et al., Laser-driven, magnetized quasi-perpendicular collisionless shocks on the large
plasma device. Physics of Plasmas (1994-present), 21(5):056312, 2014
6) C. Niemann et al., Observation of collisionless shocks in a large current-free laboratory plasma.
Geophysical Research Letters, 41(21):7413–7418, 2014
7) S. E. Clark et al., Hybrid simulation of shock formation for super-alfvénic expansion of laser
ablated debris through an ambient, magnetized plasma. Physics of Plasmas (1994-present),
20(8):082129, 2013

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