Developing a magnetized piston driver for collisionless shock experiments

Collisionless shocks are frequently inferred in astrophysical systems where abrupt structural transitions occur over scales much shorter than mean Coulomb collisions. These transitions are instead mediated by a variety of wave-particle interactions with fields, leading to plasma instabilities across the shock transition.

We present the development and first data from a platform to study collisionless shocks using a pulsed power driver. The setup fielded on the MAGPIE generator (1.4 MA, 500 ns current drive) at Imperial College utilizes two side-by-side inverse wire arrays to produce counter-streaming, supersonic flows of plasma ablated from metal wires. Similar setups have previously been used to study plasma interactions including shocks, instabilities and magnetic reconnection in the collisional regime.

To access a collisionless regime (L < λ_ii ~V⁴), the velocity difference between the flows is maximized by increasing the magnetic field accelerating the flows via the JxB force. Meanwhile, the number and thickness of wires in one array is reduced to transition from steady ablative behavior to an explosive ejection of material into the oncoming flow.

The dynamics of the interaction are captured using multi-frame, self-emission imaging (optical & XUV) and a suite of laser based diagnostics (interferometry, Thomson scattering, Faraday rotation imaging) allows the parameters and structure of the interactions to be measured.