7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

PIC Simulations of Perpendicular and Parallel Piston-Driven Shock Dynamics
in a Magnetized Plasma
P. Pongkitiwanichakul1, D. B. Schaeffer2 , W. Fox3, D. Ruffolo4
Department of Physics, Faculty of Science, Kasetsart University, Thailande-mail (speaker): peera.po@ku.th2
Department of Physics and Astronomy, University of California — Los Angeles, USA
3
Department of Astrophysical Sciences, Princeton University, USA
4
Department of Physics, Faculty of Science, Mahidol University, Thailand
1

In astrophysical systems, magnetized collisionlessshocks are frequently observed [1]. In laboratory
experiments, these shocks can be replicated on a smallerscale by using laser-driven piston plasmas in thepresence of a magnetized background plasma [2,3]. Anessential factor in these experiments is the angle (𝜃! )between the direction of shock propagation and thebackground magnetic field. This study is meant to help
with experiments and will provide valuable information
to design and understand those experiments better.
To investigate shock formation and evolution, we
conducted quasi-1D collisionless piston-driven shock
simulations, varying the shock angle from 𝜃! = 90∘ to
𝜃! = 30∘ . The results demonstrate that, regardless of theangle considered, the spatial and temporal scales ofshock formation are similar when measured using theperpendicular component of the magnetic field.

Despite having different shock angles, Figure 1 reveals
that the velocity distribution in all simulations appears
similar when observed at the same distance and time,quantified in terms of 𝜌# = 𝑚$ 𝑣% /(𝑞$ 𝐵# ) and 𝜏# =𝑚$ /(𝑞$ 𝐵# ) . Here, 𝑚$ denotes the ion mass, 𝑣%
represents the piston speed, 𝑞$ is the ion charge, and 𝐵#
corresponds to the magnetic field perpendicular to theshock propagation direction.
The piston plasma accumulates magnetic flux per unit
length, which is proportional to the average rigidity ofthe piston ions, expressed as

&! '"
(!

= 𝜌# 𝐵# . Thismagnetic flux is crucial for the shock formation process.
It serves as a minimal requirement for bending andredirecting an excessive number of incoming upstream
particles within the shock layer.
The observed constancy of the perpendicular magnetic
field can be easily explained. The time and distancerequired for shock formation are inversely proportional
to sin 𝜃! . Consequently, at lower 𝜃! values, shock
formation takes longer and covers a greater distance inabsolute units. However, since 𝐵# (perpendicularmagnetic field component) remains dominant over 𝐵∥(parallel magnetic field component), shock formation
still evolves similarly when expressed in normalized
units.
At a later stage when shocks become stationary, weexamine the extent of perpendicular heating and parallel
heating. For all considered values of 𝜃! , theperpendicular heating exhibits similarity. In the case of
𝜃! = 90∘ , the parallel heating is negligible because theparallel temperature is extremely small compared to theperpendicular temperatures. This may imply that theabsence of variation along the magnetic field suppresses
the parallel heating. Conversely, for all other 𝜃! values,
there is variation along the magnetic field in thedownstream region, making parallel heating effective.
Furthermore, this parallel heating is more pronounced forsmaller 𝜃! values.
The PIC simulations were conducted on the Summit supercomputer atthe Oak Ridge Leadership Computing Facility at the Oak Ridge NationalLaboratory. We acknowledge support by the National Science andTechnology Development Agency (NSTDA) and National ResearchCouncil of Thailand (NRCT): High-Potential Research Team Grant
Program (N42A650868), by grant RGNS 63-045 from the Office of thePermanent Secretary, Ministry of Higher Education, Science, Researchand Innovation, and from the NSRF via the Program Management Unit
for Human Resources ¥& Institutional Development, Research andInnovation (B37G660015).

References[1] Balogh A., Treumann R.A., pcss.book (2013)[2] Fox W., Fiksel G., Bhattacharjee A., Chang P.-Y.,
Germaschewski K., Hu S.X., Nilson P.M., PhRvL, 111, 225002(2013)[3] Schaeffer D.B., Fox W., Follett R.K., Fiksel G., Li C.K.,
Matteucci J., Bhattacharjee A., et al., PhRvL, 122, 245001(2019)