Evolution of an Arched Magnetized Laboratory Plasma in a Sheared Magnetic Field*

Arched magnetized structures are a common occurrence in space and laboratory plasmas (i.e. solar prominences, coronal loops). We present the results from a laboratory experiment on spatio-temporal evolution of an arched magnetized plasma (β ≈ 10³, Lundquist number ≈ 10⁴, plasma radius/ion gyroradius ≈ 20) in a sheared magnetic configuration. The arched plasma is produced using a hot-cathode lanthanum hexaboride (LaB₆) source and it evolves in an ambient magnetized plasma produced by another LaB₆ source [1, 2].  The experiment is designed to model conditions relevant to the formation and destabilization of similar structures in the solar atmosphere. The magnitude of a nearly horizontal overlying magnetic field was varied to study its effects on the writhe and twist of the arched plasma. In addition, the direction of guiding magnetic field was varied to investigate its role in formation of either forward- or reverse-S shaped plasma structures. The electrical current in the arched plasma was well below the current required to make it kink unstable. A significant increase in the writhe of the arched plasma was observed with larger magnitudes of overlying magnetic field. Forward-S shaped arched plasma was observed for a guiding magnetic field oriented nearly anti-parallel to the initial arched plasma current, while the parallel orientation yielded the reverse-S shaped arched plasma.

(1) Tripathi and Gekelman, Phys. Rev. Lett. 105, 075005 (2010) 

(2) Tripathi and Gekelman, Solar Phys. 286, 479 (2013)