Session UM9: Mini-Conference on Bridging the Divide Between Space and Laboratory Plasma Physics II

The development and stability of non-thermal plasma in space

This talk will review our understanding of non-thermal ion and electron velocity distribution functions (VDFs) in space plasma, with a focus on pressure anisotropy and unequal temperatures in the solar wind and corona. Under typical solar wind plasma conditions, which are common for a range of astrophysical plasmas, relaxation processes such as Coulomb collisions are sufficiently slow compared to interactions between particles and electromagnetic fluctuations that ion and electron VDFs can depart significantly from the classical Maxwell-Boltzmann distribution and maintain these non-thermal features for times greater than the dynamical scales of the system. These non-thermal properties of the plasma are very important as they can significantly modify aspects of the plasma such as heat flux, susceptibility to kinetic instabilities, and interaction with waves and turbulence. Major open questions in the field will be reviewed, along with current and planned observational capabilities of instruments on spacecraft such as Wind and the upcoming Parker Solar Probe, with an eye to potential crossover with laboratory plasma experiments.   

Energy Transformation between Forms in the Big Red Ball

Astrophysical and Space plasmas are often characterized by quasi-stationary magnetized plasmas which are both pressure dominated ($\beta\se 1$) and flow dominated ($M_{A} = V/V_{A}>1$), and yet still behave as ideal plasmas with fluid and magnetic Reynolds numbers being large so that magnetic fields are frozen into the flowing, often turbulent plasma ($Rm\gg 1, Re \gg 1$). Such natural plasmas are almost always converting energy of one form into another. For example, dynamos convert plasma flow energy into magnetic fields; magnetic reconnection controls how magnetic energy is released into plasma flow and heat. The Big Red Ball is a device at the core of flexible new user facility (the Wisconsin Plasma Physics Laboratory---WiPPL) designed to study a range of astrophysically relevant plasma processes in this unique regime. This talk will describe the unique capabilities of BRB, along with several experiments, in both operating and planning stages, that illustrate its possibilities a range of astrophysical experiments, including self-exciting dynamos, collisionless magnetic reconnection, plasma accretion via the magneto-rotational instability [MRI], jet stability, stellar winds and shocks.   

Unraveling the physics of magnetic reconnection: the interaction of laboratory and space observations with models

Reconnection leads to impulsive conversion of magnetic energy into high-speed flows, plasma heating and the production of energetic particles. A major challenge has been to account for the enormous range of spatial scales in systems undergoing reconnection. Progress on the topic has been facilitated by the observations in space and the laboratory with models bridging the divide. Understanding the mechanisms for fast reconnection is a historical example. However, in this talk I will focus on reconnection in asymmetric systems -- those with large ambient gradients in the pressure or density. The interest in the topic has been driven by efforts to understand when and where reconnection takes place in the laboratory (tokamaks) and in space (planetary magnetospheres and the solar wind). Ideas on reconnection suppression due to diamagnetic drifts have produced a unified picture of the conditions required for reconnection onset over a wide range of environments. Observations from the MMS mission have provided an extraordinary window into reconnection at the Earth's magnetopause, including the mechanisms for magnetic energy dissipation and the role of turbulence. Finally, the prospects for establishing the mechanisms for energetic particle production will be addressed.   

Plasma heating across quasi-perpendicular shocks observed by the MMS mission

Collisionless shocks are one of the most fundamental nonlinear phenomena that involve intense plasma heating and acceleration in space and astrophysical systems. Despite decades of efforts, the key physics underlying electron and ion heating remains unsolved. The continuous 3D high accuracy high cadence data from the Magnetospheric Multiscale (MMS) mission have revealed a drastically different picture on electron and ion heating in our preliminary examination of a number of bow shock crossings. In particular, the MMS measurements of 3D plasma distribution functions that are orders of magnitude higher cadence than ever indicate an intimate relation between the key thermalization phase of ions, the anisotropic temperature increase of electrons, and intense wave fluctuations. Open questions will be posted for computational studies and laboratory experiments on collisionless shocks.   

FLARE: A New User Facility for Laboratory Studies of Multiple-Scale Physics of Magnetic Reconnection and Related Phenomena in Heliophysics and Astrophysics

The FLARE device (Facility for Laboratory Reconnection Experiments; flare.pppl.gov) is a new laboratory experiment under construction at Princeton with first plasmas expected in the fall of 2017, based on the design of Magnetic Reconnection Experiment (MRX; mrx.pppl.gov) with much extended parameter ranges. Its main objective is to provide an experimental platform for the studies of magnetic reconnection and related phenomena in the multiple X-line regimes directly relevant to space, solar, astrophysical and fusion plasmas. The main diagnostics is an extensive set of magnetic probe arrays, simultaneously covering multiple scales from local electron scales ($\sim$2 mm), to intermediate ion scales ($\sim$10 cm), and global MHD scales ($\sim$1 m). Specific example space physics topics which can be studied on FLARE will be discussed.   

Resonant drag instabilities in fluids and plasmas

Many plasma instabilities, for instance two-stream instabilities or the magnetorotational instability, arise due to a resonance between two or more oscillation frequencies of the system. In this talk, I will introduce a general method for understanding, and calculating the properties of, such resonant instabilities. Application to dust-laden fluids and plasmas has uncovered a variety of new instabilities that occur when dust moves with a relative speed that matches the phase velocity of a fluid wave. These have interesting astrophysical applications for systems ranging from galactic winds to protoplanetary accretion disks. I will also discuss applications to other systems, for instance plasmas with a population of streaming cosmic rays, or resonant instabilities in collisionless plasmas.   

New insights into kinetic plasma turbulence via model comparisons

The nature of plasma turbulence at kinetic scales has received a lot of attention recently, also driven by the availability of new observational data and unprecedented computational capabilities. Here, we carry out the first such investigation via a systematic comparison between different kinetic models of a turbulent collisionless plasma. The models considered include a fully-kinetic description, two widely used reduced models (gyrokinetic and hybrid-kinetic with fluid electrons), and a novel reduced gyrokinetic approach. This is a significant step towards addressing the "turbulent dissipation challenge" which has been called for in recent years. Based on our results, we can clarify several open questions regarding the character of turbulence in the solar wind.   

Bayesian Techniques for Plasma Theory to Bridge the Gap Between Space and Lab Plasmas

We will show how Bayesian techniques provide a general data analysis methodology that is better suited to investigate phenomena that require a nonlinear theory for an explanation. We will provide short examples of how Bayesian techniques have been successfully used in the radiation belts to provide precise nonlinear spectral estimates of whistler mode chorus and how these techniques have been verified in laboratory plasmas. We will demonstrate how Bayesian techniques allow for the direct competition of different physical theories with data acting as the necessary arbitrator.   

Understanding Turbulence using Active and Passive Multipoint Measurements in Laboratory Magnetospheres

In a laboratory magnetosphere, plasma is confined by a strong dipole magnet, and interchange and entropy mode turbulence\footnote{Garnier, \textit{et al.}, \textit{Phys Plasmas}, \textbf{24}, 012506 (2017).} can be studied and controlled in near steady-state conditions.\footnote{Roberts, \textit{et al.}, \textit{Phys Plasmas}, \textbf{22}, 055702 (2015).} Turbulence is dominated by long wavelength modes exhibiting chaotic dynamics, intermitency, and an inverse spectral cascade. Here, we summarize recent results: (\textit{i}) high-resolution measurement of the frequency-wavenumber power spectrum using Capon's ``maximum likelihood method'',\footnote{Qian, \textit{et al.}, \textit{Undergraduate Poster Session; This meeting.}} and (\textit{ii}) direct measurement of the nonlinear coupling of interchange/entropy modes in a turbulent plasma through driven current injection at multiple locations and frequencies.\footnote{Abler, \textit{et al.}, \textit{Poster Category 1.8; This meeting.}} These observations well-characterize plasma turbulence over a broad band of wavelengths and frequencies. Finally, we also discuss the application of these techniques to space-based experiments and observations aimed to reveal the nature of heliospheric and magnetospheric plasma turbulence.