Implementation of an unequal path length, heterodyne interferometer on the MOCHI LabJet experiment

Abstract

The MOCHI LabJet experiment aims to explore the stability of magnetic flux tubes through the medium of laboratory astrophysical plasmas. The boundary conditions of large gravitational bodies, namely accretion disks, are replicated and allowed to influence a plasma over short timescales. Observation of the plasma is enabled through use of a variety of fast diagnostics, including an unequal path length, heterodyne, quadrature phase differential interferometer, the development and implementation of which is described in detail. The LabJet gun, a triple-electrode planar plasma gun featuring azimuthally symmetric gas injection achieves a new, long-duration, highly-stabilized, jet plasma formation. The line-integrated density in this new LabJet formation is found to be (nL) = (6 +/- 3)x10^2 [m^-2]. By observing the axial expansion rate of the jet over multiple chord locations (all perpendicular to the propagation axis), the interferometer provides an Alfv\'en velocity measurement of v_A = 41.3 +/- 5.4 [km/s], which at the jet density observed indicates an axial magnetic field strength of B_z = 0.15 +/- 0.04 [T]. Various other laboratory components are also detailed, such as a shot-based MDSplus data storage architecture implemented into the LabVIEW experiment control code, and the production and performance of ten fast neutral gas injection valves which when fired in unison provide a total particle inventory of (7.8 +/- 0.6)x10^23 [HI particles].