Jason Milhone

Jason Milhone

Graduate research assisant at the Wisconsin Plasma Physics Laboratory (WiPPL) studying astrophysical plasma processes in the lab.

Publications

A laboratory model for the Parker spiral and magnetized stellar winds

Published in Nature Physics, 2019

Many rotating stars have magnetic fields that interact with the winds they produce. The Sun is no exception. The interaction between the Sun’s magnetic field and the solar wind gives rise to the heliospheric magnetic field—a spiralling magnetic structure, known as the Parker spiral, which pervades the Solar System. This magnetic field is critical for governing plasma processes that source the solar wind. Here, we report the creation of a laboratory model of the Parker spiral system based on a rapidly rotating plasma magnetosphere and the measurement of its global structure and dynamic behaviour. This laboratory system exhibits regions where the plasma flows evolve in a similar manner to many magnetized stellar winds. We observe the advection of the magnetic field into an Archimedean spiral and the ejection of quasi-periodic plasma blobs into the stellar outflow, which mimics the observed plasmoids that fuel the slow solar wind. This process involves magnetic reconnection and can be modelled numerically by the inclusion of two-fluid effects in the simulation. The Parker spiral system mimicked in the laboratory can be used for studying solar wind dynamics in a complementary fashion to conventional space missions such as NASA’s Parker Solar Probe mission.

Recommended citation: Peterson, E. E., Endrizzi, D. A., Beidler, M., Bunkers, K. J., Clark, M., Egedal, J., … Forest, C. B. (2019). A laboratory model for the Parker spiral and magnetized stellar winds. Nature Physics. https://doi.org/10.1038/s41567-019-0592-7

A spectrometer for high-precision ion temperature and velocity measurements in low-temperature plasmas

Published in Review of Scientific Instruments, 2019

We have developed a low-cost spectrometer with simple optical design that achieves unprecedented precision measurements of ion temperature (±0.01 eV) and velocity (±20 m/s). A Fabry-Pérot étalon provides the simultaneous high resolving power and high throughput needed for the light levels available in singly ionized helium and argon plasmas. Reducing the systematic uncertainty in the absolute wavelength calibration needed for the specified velocity precision motivates a Bayesian analysis method called Nested Sampling to address the nontrivial uncertainty in the diffraction order. An initial emission measurement of a singly charged stationary argon plasma yields a temperature of 0.339 ± 0.007 eV and a velocity of −3 ± 4 m/s with a systematic uncertainty of 20 m/s.

Recommended citation: Milhone, J., Flanagan, K., Nornberg, M. D., Tabbutt, M., & Forest, C. B. (2019). A spectrometer for high-precision ion temperature and velocity measurements in low-temperature plasmas. Review of Scientific Instruments, 90(6), 063502. https://doi.org/10.1063/1.5092966

High ionisation fraction plasmas in a low temperature, multidipole cusp plasma

Published in Journal of Plasma Physics, 2018

The depletion of neutral helium atoms has been studied in an unmagnetised spherical plasma created by DC discharge in a multidipole confinement field. Knowing the neutral density profile is critical to predicting the equilibrium flow of such plasmas. A model of the emissivity due to electron-impact excitation of neutral atoms in the plasma has been derived and used to fit radiance measurements of several neutral transitions to extract the radial profile of neutral density for plasmas of varying temperature and density. We report a depletion of the core neutral density varying between negligible levels to 80 % of the edge neutral density depending on the input power and fuelling. The corresponding ionisation fraction varies between 30–80 % in the plasma core. A simple neutral diffusion model is sufficient to describe the shape of neutral density profile implied by the radiance measurements. We have used the measurements to include a drag force due to neutral charge-exchange collisions in simulations of driven plasma flow. The simulation predicts a better fit to Mach probe flow measurements when this neutral drag is accounted for. This work shows that accounting for a realistic neutral profile is important to predict the plasma flow geometry and its magnetohydrodynamics (MHD) stability.

Recommended citation: Désangles, V., Milhone, J., Cooper, C., Weisberg, D. B., Nornberg, M. D., & Forest, C. B. (2018). High ionisation fraction plasmas in a low temperature, multidipole cusp plasma. Journal of Plasma Physics, 84(3), 905840312. https://doi.org/10.1017/S0022377818000533