Parallel shock-relevant whistler waves and reflected ions driven by a coaxial plasma gun

A flexible laboratory configuration on the Big Red Ball device has been created for studying the physics of parallel shock formation by firing a coaxial plasma gun into a pre-existing plasma along the direction of the background magnetic field. At Alfvén Mach numbers near upper M Subscript upper A Baseline tilde 2.4 M A ∼ 2.4 $M_A \sim 2.4$ , we observe this plasma gun piston initiate a dispersive whistler pulse and reflect ions that are collisionless against the background. These reflected ions are focused into an on-axis bunch by a concave-forward potential structure specific to the cylindrical geometry. Resonance of these reflected ions with the dispersive whistler waves, though not observed in the experiment, is a potential mechanism for collisionless shock formation.