The Mochi.LabJet experiment for measurements of canonical helicity injection in a laboratory astrophysical jet

TL;DR

The Mochi.LabJet experiment creates laboratory plasma jets that mimic astrophysical jets, using a novel setup with controlled electric and magnetic fields, providing insights into jet stability and formation.

Contribution

This paper introduces the Mochi device and LabJet configuration, a new experimental setup for producing and studying stable, collimated plasma jets in the laboratory.

Findings

Successfully produced short-lived collimated plasma jets.

Achieved long-lived, flow-stabilized magnetic jets with high aspect ratios.

Measured plasma parameters consistent with astrophysical jet conditions.

Abstract

The Mochi device is a new pulsed power plasma experiment designed to produce long, collimated, stable, magnetized plasma jets when set up in the LabJet configuration. The LabJet configuration aims to simulate an astrophysical jet in the laboratory by mimicking an accretion disk threaded by a poloidal magnetic field with concentric planar electrodes in front of a solenoidal coil. The unique setup consists of three electrodes, each with azimuthally symmetric gas slits. Two of the electrodes are biased independently with respect to the third electrode to control the radial electric field profile across the poloidal bias magnetic field. This design approximates a shear azimuthal rotation profile in an accretion disk. The azimuthally symmetric gas slits provide a continuously symmetric mass source at the footpoint of the plasma jet, so any azimuthal rotation of the plasma jet is not hindered by a discrete number of gas holes. The initial set of diagnostics consists of current Rogowski coils, voltage probes, magnetic field probe arrays, an interferometer and ion Doppler spectroscopy, supplemented by a fast ion gauge and a retarding grid energy analyzer. The measured parameters of the first plasmas are 1E22 m-3, 0.4 T, 5-25 eV, with velocities of 20-80 km/s. The combination of a controllable electric field profile, a flared poloidal magnetic field, and azimuthally symmetric mass sources in the experiment successfully produces short-lived (10 {\mu}s, >5 Alfv\'en times) collimated magnetic jets with ~10:1 aspect-ratio and long-lived (100 {\mu}s, >40 Alfv\'en times) flow-stabilized, collimated, magnetic jets with ~30:1 aspect-ratio.