Session VP16: Poster Session: Space Physics (2:00pm - 5:00pm)

Braided Structure in an Experiment Simulating a Solar Corona Loop

Braiding of a multitude of solar corona loops, first proposed by Parker $^{\mathrm{[1]}}$, may explain loop non-monolithic structure and eruption dynamics. Braiding of multiple loops has been observed by the High-Resolution Coronal Imager $^{\mathrm{[2]}}$. We now observe braiding of multiple loops in a new arrangement of the Caltech lab experiment replicating solar coronal loops. The multiple loops are achieved by having multiple gas injection nozzles on each of the two electrodes representing the solar surface. We further observe that a single strand of the multi-loop braided structure can undergo a magnetic Rayleigh Taylor Instability (RTI) driven by hoop force. We are exploring how parameters such as axial magnetic field and gas injection position affect the braided structures and their undergoing the RTI. We will also be investigating whether X-ray bursts develop as was observed in a previous configuration where there was only a single loop and so no braided structure of multiple loops. [1] E. N. Parker. The Astrophysical Journal 174 (1972): 499. [2] J. W. Cirtain, et al. Nature 493.7433 (2013): 501-503.   

Turbulence analysis using multi-point, multi-scale spacecraft observations

There are many fundamental open questions about the structure and dynamics of turbulence in weakly collisional plasmas. Answering these questions is complicated by the multi-scale nature of the turbulent transfer of mass, momentum, and energy, with characteristic temporal and spatial scales spanning many orders of magnitude. The solar wind is an ideal environment in which to measure turbulence, but multi-point observations with spacecraft separations spanning these scales are needed to simultaneously characterize structure and cross-scale turbulent transfer. This work uses synthetic multi-point spacecraft data recorded from numerical simulations to demonstrate the utility of multi-point, multi-scale measurements, in preparation for data from such future multi-spacecraft observatories. In particular, we use the baseline orbit design for the HelioSwarm mission concept to explore the effects of different inter-spacecraft separations and geometries on the accuracy of the measured turbulence properties.   

Surface Mounted Impedance Probe Antenna as a ThinSat Spacecraft Payload

Collaborations utilizing small spacecraft in near earth orbit between the U. S. Coast Guard Academy (CGA), Navy Research Lab (NRL), the U. S. Naval Academy (USNA), and the Air Force Institute of Technology (AFIT) have initiated scientific and engineering space -based experiments. We have constructed an impedance probe payload for launch in Fall 2021 derived from the existing `Space PlasmA Diagnostic suitE' (SPADE) mission operating from NASA's International Space Station. Currently both space and laboratory plasmas are investigated with AC impedance measurements using a radio frequency antenna. Plasma electron density data collected from the ThinSat will however use an innovative surface mounted dipole antenna to gather the required sheath-plasma and plasma resonance information. On that same launch, a compact multispectral `Pixel Sensor' with a 450 nm - 1000 nm spectral range will add to the existing Inertial Motion Unit, Temperature Sensor, Infrared Sensor, and Energetic Particle Detector baselined in previous launches. We have designed, built, and assembled custom components while and NRL will test the functionality of the antenna in their Space Plasma Simulation Chamber then low altitude launch tests will be conducted. Impedance probe optimization, data collection obstacles, solutions, and procedures will be reported.   

A Drift-Kinetic Method for Obtaining Gradients in Plasma Properties from Single-Point Distribution Function Data

We derive a new drift-kinetic method for estimating gradients in the plasma properties through a velocity space distribution at a single point. The gradients are intrinsically related to agyrotropic features of the distribution function. This method predicts the gradients in the magnetized distribution function, and can predict gradients of arbitrary moments of the gyrotropic background distribution function. The method allows for estimates on density andpressure gradients on the scale of a Larmor radius, proving to resolve smaller scales than any method currently available to spacecraft. The model is verified with a set of fully-kinetic VPIC particle-in-cell simulations.   

A Spectral Electrostatic Particle-in-Cell Algorithm with Sparse Grid and Exact Energy Conservation

The standard particle-in-cell (PIC) method employs explicit finite-difference (FD) methods (e.g. the leap-frog scheme) for both spatial and temporal integrations. Here we employ a sparse-grid pseudo-spectral method for solving the Poisson equation [1] and a fully implicit time integration to achieve exact energy conservation. The advantage of the pseudo-spectral field solver is its spectral accuracy in solving the field solutions. The introduction of the sparse-grid technique to PIC [1] has the potential of mitigating the curse of dimensionality, which may dramatically reduce the number of simulated particles to achieve satisfactory statistical resolution. Earlier studies of implicit time integration of PIC FD equations can enforce exact energy exchange between field and particles, resulting exact energy-conserving schemes [2]. We prove that the energy-conserving scheme can be carried over to the pseudo-spectral scheme, and to sparse grids. We demonstrate the new scheme in a 2D electrostatic PIC code. Theoretical results are confirmed via numerical examples. [1] L. F. Ricketson and A. J. Cerfon. Plasma Physics and Controlled Fusion 59.2 (2016): 024002. [2] G. Chen, Luis Chacón, and Daniel C. Barnes. Journal of Computational Physics 230.18 (2011): 7018-7036.   

Radioastronomical Diagnostics of Solar Wind Plasma in the Light of Parker Solar Probe

The Solar Wind plasma is important for testing many fundamental questions in plasma physics, such as the nature of MHD turbulence. This field is being revolutionized by the Parker Solar Probe spacecraft, which is making direct measurements at heliocentric distances as small as 0.13 astronomical units or 27 solar radii. In this paper, I discuss radioastronomical propagation measurements that also yield information on the Solar Wind plasma, over heliocentric distances as small as 2-3 solar radii. The motivations for this comparison are (1) radioastronomical measurements are complementary to the point measurements made by Parker Solar Probe, and (2) a comparison provides a ``ground truth'' check of radio measurements, which are the only means to probe interstellar turbulence. The plasma turbulence parameters that can be probed by both techniques are (1) the dependence of the turbulence power spectra on heliocentric distance, (2) the speed at which the turbulent irregularities propagate with respect to the Solar Wind rest frame, (3) the dependence of the outer scale of turbulence on heliocentric distance, and (4) the form of the turbulence spectra in the dissipation range.   

The relative heating of ions and electrons due to turbulent dissipation through Landau damping

The relative heating of ions and electrons due to turbulent dissipation plays a crucial role in the thermodynamics in many weakly collisional plasmas, including the solar wind. Previous works have evaluated the radial profile of these heating rates as a function of the distance from the Sun using data from in situ observations made by missions including Helios, Ulysses, and Voyager, making a variety of theoretical assumptions regarding the turbulent distribution of power and the accessible damping mechanisms. These in situ measurements of the solar wind have been limited to a heliocentric distance of greater than 0.29 au from the Sun's surface. Parker Solar Probe (PSP) will eventually provide such measurements down to 0.046 au. One particular theoretical model, developed in Howes et al 2008 and expanded in Kunz et al 2018, determines relative heating rates as a function of proton and electron anisotropic temperatures and plasma beta for a steady-state cascade of wavevector anisotropic turbulent fluctuations when dissipation is mediated through Landau damping. We apply this model to observations from the first two perihelion of PSP, characterizing how the relative heating rates vary as a function of radial distance, plasma parameters, and solar wind source, illuminating how energy is partitioned in the young solar wind.   

Stability analysis of electron core-strahl solar wind distributions

In this work, we perform kinetic stability analysis of a solar wind electron distribution made up of core and strahl subpopulations. Following up from work in (Horaites et. al. 2018), the core population is modeled as a drifting Maxwellian and the strahl population by an analytic expression derived in (Horaites et. al. 2019) from a drift kinetic equation. The expression for the strahl distribution used in this work differs from the previous work as the equation generalizes to electrons at all energies rather than a limiting case of suprathermal particles. Stability analysis is performed with the LEOPARD solver (Astfalk et. al. 2017), a linear dispersion solver that inputs arbitrary gyrotropic distribution functions for a magnetized plasma. Stability of kinetic Alfven, magnetosonic, and whistler modes is accessed at oblique angles of propagation at a range of spacial scales. Whistler turbulence has been invoked as a source of anomalous scattering of strahl electrons, so particular interest is taken in whistler modes. (1) Astfalk P., Jenko F., 2017, JGR (Space Phys.), 122, 89. (2) Horaites K., Astfalk P., Boldyrev S., Jenko F., 2018, MNRAS 480, 1499-1506. (3) Horaites K., Boldyrev S., 2019, MNRAS 489, 3412--3419.   

Predicting the Velocity-Space Signatures of Particle Energization in Turbulence and Instabilities using Linear Kinetic Theory

Illuminating the kinetic mechanisms of particle energization is the key to understanding how kinetic turbulence, collisionless magnetic reconnection, particle acceleration, and instabilities impact the evolution of important heliospheric environments. With the increasing availability of both high cadence, high phase-space resolution spacecraft data and massively parallel nonlinear kinetic simulations of weakly collisional heliospheric plasmas, it is critical to develop tools to examine the kinetic physics of particle energization. The field-particle correlation technique is an innovative new method that can be used to characterize and distinguish different mechanisms of particle energization underlying these important plasma processes. Here we use linear gyrokinetic and linear Vlasov-Maxwell theory to produce analytical predictions for the velocity-space signatures of collisionless damping mechanisms as well as the energy transfer from particles to fields in kinetic instabilities.   

Tunneling of Whistler Waves in a Simplified Model of the Upper Ionosphere-Lower Magnetosphere

In this work, tunneling has been identified in a dipole model of the Earth’s magnetosphere. Because the mix of ion species in the lower magnetosphere varies with altitude, the lower-hybrid resonance can occur at two distinct altitudes. These surfaces are known to be important to the magnetospheric reflection of whistler waves, where a whistler wave traveling down from high altitude can be reflected back. However, when the two resonance surfaces are close enough to each other, tunneling transfers energy from the incoming wave to both a reflected wave and a transmitted wave. The reflected wave returns to the magnetosphere, while the transmitted wave continues down into the ionosphere. We have developed a simplified model of the magnetospheric plasma that illustrates this tunneling of whistler waves. We show how a ray splitting algorithm can be used to compute the effect of tunneling on the wave dynamics in this simplified system. Future applications of the ray splitting algorithm to ray tracing calculations in realistic magnetospheric plasmas will be outlined.