Princeton Center for Heliophysics Seminar

A new experiment, called the PHAse Space MApping (PHASMA) experiment, features laser induced fluorescence diagnostics for ion measurements, Thomson scattering diagnostics for electron velocity distribution function measurements, and a microwave scattering system for turbulence measurements. PHASMA is designed to enable the direct measurement of ion and electron vdfs in space-relevant plasma phenomena including reconnection, shocks, and turbulence. To create the conditions necessary for different experimental regimes, PHASMA employs a 1 kW, steady-state helicon source capable of generating variable-density background hydrogen, helium, argon, krypton, and xenon plasmas with controllable plasma pressure (relative to the magnetic pressure), collisionality, and azimuthal flow shear. Reconnecting flux ropes arise through the merging of discharges from two pulsed plasma guns that operate in argon, helium, and hydrogen. In this talk I will describe results from two recent, space-relevant, experimental campaigns. The first campaign explored the stability of non-line-tied flux ropes. Similar boundary conditions exist for flus ropes observed in space and the solar corona. The measurements confirm the theoretically predicted stability threshold for the ropes and indicate that the m = 1 kink instability triggered for large currents in the flux rope drives an additional Alfvénic mode that propagates along the flux rope. In the second campaign, the merger of two flux ropes through electron-only reconnection is investigated at the kinetic, sub-gyroradius, scale. We find that the majority of the incoming magnetic energy appears as electron thermal energy and that Ohmic processes are unlikely to be responsible for the measured increase in electron enthalpy.  The electron distribution function measurements include non-Maxwellian features, including beams that jet out from the X-point in both outflow directions. The electron beam speed scales with the local electron Alfvén speed.