Speaker
Eleanor Tubman
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.402.pdf
Experimental studies of bow shocks formed in supersonic plasma flows
with varying advected magnetic fields.
E. R. Tubman1, S. V. Lebedev1, G. C. Burdiak1, S. N. Bland1, T. Clayson1, J. W. D. Halliday1,
J. Hare1, D. Russell1, L. Suttle1, F. Suzuki-Vidal1
1
Imperial College, London, UK
Bow shocks are ubiquitous within astrophysics, formed when supersonic, magnetised
material interacts with an obstacle and disruptions occur in the flow. In this presentation
we discuss novel results collected from using from a pulsed power platform to control the
magnetic fields carried within the plasma and influence the bow shocks created.
The supersonic, super-Alfvenic plasma flows (vflow ~ 70 km/s, MA >2.5) were produced
using the MAGPIE facility at Imperial College driving a ~1 MA, 500 ns current pulse
through either wire arrays [1] or planar foils [2]. The plasma flow carries a frozen-in
magnetic field (B~ 1-2 T) which influences the bow shock structure formed at obstacle
interfaces [3]. Obstacles of various dimensions are placed into the plasma flow and
designed to mimic various scenarios including the understanding of bow shocks formed at
the interface with projectiles sent through Earth’s atmosphere. Further investigations have
been performed to reduce the magnetic fields carried by the plasma using parallel bar
grids orientated such that the bars are perpendicular to the frozen-in magnetic field
direction.
We also discuss an instability developing at the obstacle in the layer of the stagnated
plasma. The k-vector of the instability is oriented along the obstacle surface and is in the
direction normal to the magnetic field. Faraday rotation measurements indicate that the
instability leads to the modulation of the magnetic field strength in the plasma. Various
diagnostics including Thomson scattering, two-colour laser interferometry,
shadowgraphy and magnetic probes are used to characterize the flow velocity,
temperature, density and magnetic field. By controlling the initial magnetic field
magnitude, the density of the plasma and recording the temporal evolution of this feature a
better understanding of the underlying seed of the instability can be gained.
[1] A. J. Harvey-Thompson et al., PoP 16, (2009)
[2] F. Suzuki-Vidal et al., Astrophys. J. 815, 2 (2015)
[3] G. C. Burdiak et al., PoP 24, 2017
