PATCH: Particle Arrival Time Correlation for Heliophysics

The ability to understand the fundamental nature of the physics that governs the heliosphere requires spacecraft instrumentation to measure energy transfer at kinetic scales. This translates to a time cadence resolving the proton kinetic timescales, typically of the order of the proton gyrofrequency. The downlinked survey-mode data from modern spacecraft are often much lower resolution than this criterion, meaning that the higher resolution, burst-mode data must be captured to study an event at kinetic time scales. Telemetry restrictions, however, prohibit a sizable fraction of this burst-mode data from being downlinked to the ground. The field-particle correlation (FPC) technique can quantify kinetic-scale energy transfer between electromagnetic fields and charged particles and identify the mechanisms responsible for mediating the transfer. In this study, we adapt the FPC technique for calculating wave-particle energy transfer onboard modern spacecraft using time-tagged particle counts simultaneous with electromagnetic field measurements. The newly developed procedure, called Particle Arrival Time Correlation for Heliophysics (PATCH), is tested using synthetic spacecraft data, where output from a gyrokinetic plasma turbulence simulation was downsampled to Parker Solar Probe (PSP) energy-angle resolution. We assess the ability of the PATCH algorithm to recover the qualitative and quantitative features of the resulting velocity-space signatures, such as ion-Landau damping, that can be used to distinguish different kinetic mechanisms of particle energization. Ultimately, we demonstrate a proof-of-concept that the PATCH method could enable calculations of onboard wave-particle correlations, with the intent of enhancing spacecraft data return by several orders of magnitude. © 2021. American Geophysical Union. All Rights Reserved.6 month embargo; published online: 10 May 2021This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Determining Threshold Instrumental Resolutions for Resolving the Velocity-Space Signature of Ion Landau Damping

Unraveling the physics of the entire turbulent cascade of energy in space and astrophysical plasmas from the injection of energy at large scales to the dissipation of that energy into plasma heat at small scales, represents an overarching, open question in heliophysics and astrophysics. The fast cadence and high phase-space resolution of particle velocity distribution measurements on modern spacecraft missions, such as the recently launched Parker Solar Probe, presents exciting new opportunities for identifying turbulent dissipation mechanisms using in situ measurements of the particle velocity distributions and electromagnetic fields. Here we demonstrate how to use data from kinetic numerical simulations of plasma turbulence to create synthetic spacecraft data; this data set can then be used to determine instrumental requirements to identify specific particle energization mechanisms. Using such synthetic data, downsampled to the velocity phase-space resolution available from the plasma instruments on several past and present missions, we compute the resulting velocity-space signature of ion Landau damping using the recently developed Field-Particle Correlation (FPC) technique. We find that only recent missions have sufficiently fine phase-space resolution to resolve the characteristic resonant features of the ion Landau damping signature. Coupled with numerical determinations of the velocity-space signatures of different proposed particle energization mechanisms, this strategy enables the specification of instrumental capabilities required to achieve science goals on the topic of plasma heating and particle acceleration in turbulent heliospheric plasmas. © 2021. American Geophysical Union. All Rights Reserved.6 month embargo; published online: 10 May 2021This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Determining Threshold Instrumental Resolutions for Resolving the Velocity‐Space Signature of Ion Landau Damping

Unraveling the physics of the entire turbulent cascade of energy in space and astrophysical plasmas from the injection of energy at large scales to the dissipation of that energy into plasma heat at small scales, represents an overarching, open question in heliophysics and astrophysics. The fast cadence and high phase-space resolution of particle velocity distribution measurements on modern spacecraft missions, such as the recently launched Parker Solar Probe, presents exciting new opportunities for identifying turbulent dissipation mechanisms using in situ measurements of the particle velocity distributions and electromagnetic fields. Here we demonstrate how to use data from kinetic numerical simulations of plasma turbulence to create synthetic spacecraft data; this data set can then be used to determine instrumental requirements to identify specific particle energization mechanisms. Using such synthetic data, downsampled to the velocity phase-space resolution available from the plasma instruments on several past and present missions, we compute the resulting velocity-space signature of ion Landau damping using the recently developed Field-Particle Correlation (FPC) technique. We find that only recent missions have sufficiently fine phase-space resolution to resolve the characteristic resonant features of the ion Landau damping signature. Coupled with numerical determinations of the velocity-space signatures of different proposed particle energization mechanisms, this strategy enables the specification of instrumental capabilities required to achieve science goals on the topic of plasma heating and particle acceleration in turbulent heliospheric plasmas. © 2021. American Geophysical Union. All Rights Reserved.6 month embargo; published online: 10 May 2021This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

In Situ Signature of Cyclotron Resonant Heating in the Solar Wind

The dissipation of magnetized turbulence is an important paradigm for describing heating and energy transfer in astrophysical environments such as the solar corona and wind; however, the specific collisionless processes behind dissipation and heating remain relatively unconstrained by measurements. Remote sensing observations have suggested the presence of strong temperature anisotropy in the solar corona consistent with cyclotron resonant heating. In the solar wind, in situ magnetic field measurements reveal the presence of cyclotron waves, while measured ion velocity distribution functions have hinted at the active presence of cyclotron resonance. Here, we present Parker Solar Probe observations that connect the presence of ion-cyclotron waves directly to signatures of resonant damping in observed proton-velocity distributions using the framework of quasilinear theory. We show that the quasilinear evolution of the observed distribution functions should absorb the observed cyclotron wave population with a heating rate of 10-14 W/m3, indicating significant heating of the solar wind. © 2022 American Physical Society.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Revolutionizing Our Understanding of Particle Energization in Space Plasmas Using On-Board Wave-Particle Correlator Instrumentation

A leap forward in our understanding of particle energization in plasmas throughout the heliosphere is essential to answer longstanding questions in heliophysics, including the heating of the solar corona, acceleration of the solar wind, and energization of particles that lead to observable phenomena, such as the Earth’s aurora. The low densities and high temperatures of typical heliospheric environments lead to weakly collisional plasma conditions. Under these conditions, the energization of particles occurs primarily through collisionless interactions between the electromagnetic fields and the individual plasma particles with energies characteristic of a particular interaction. To understand how the plasma heating and particle acceleration impacts the macroscopic evolution of the heliosphere, impacting phenomena such as extreme space weather, it is critical to understand these collisionless wave-particle interactions on the characteristic ion and electron kinetic timescales. Such understanding requires high-cadence measurements of both the electromagnetic fields and the three-dimensional particle velocity distributions. Although existing instrument technology enables these measurements, a major challenge to maximize the scientific return from these measurements is the limited amount of data that can be transmitted to the ground due to telemetry constraints. A valuable, but underutilized, approach to overcome this limitation is to compute on-board correlations of the maximum-cadence field and particle measurements to improve the sampling time by several orders of magnitude. Here we review the fundamentals of the innovative field-particle correlation technique, present a formulation of the technique that can be implemented as an on-board wave-particle correlator, and estimate results that can be achieved with existing instrumental capabilities for particle velocity distribution measurements. Copyright © 2022 Howes, Verniero, Larson, Bale, Kasper, Goetz, Klein, Whittlesey, Livi, Rahmati, Chen, Wilson, Alterman and Wicks.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Inferred Linear Stability of Parker Solar Probe Observations Using One- And Two-component Proton Distributions

The hot and diffuse nature of the Sun's extended atmosphere allows it to persist in non-equilibrium states for long enough that wave-particle instabilities can arise and modify the evolution of the expanding solar wind. Determining which instabilities arise, and how significant a role they play in governing the dynamics of the solar wind, has been a decades-long process involving in situ observations at a variety of radial distances. With new measurements from the Parker Solar Probe (PSP), we can study what wave modes are driven near the Sun, and calculate what instabilities are predicted for different models of the underlying particle populations. We model two hours-long intervals of PSP/SPAN-i measurements of the proton phase-space density during the PSP's fourth perihelion with the Sun using two commonly used descriptions for the underlying velocity distribution. The linear stability and growth rates associated with the two models are calculated and compared. We find that both selected intervals are susceptible to resonant instabilities, though the growth rates and kinds of modes driven unstable vary depending on whether the protons are modeled using one or two components. In some cases, the predicted growth rates are large enough to compete with other dynamic processes, such as the nonlinear turbulent transfer of energy, in contrast with relatively slower instabilities at larger radial distances from the Sun. © 2021. The American Astronomical Society. All rights reserved..Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Strong Perpendicular Velocity-space Diffusion in Proton Beams Observed by Parker Solar Probe

International audienceAbstract The SWEAP instrument suite on Parker Solar Probe (PSP) has detected numerous proton beams associated with coherent, circularly polarized, ion-scale waves observed by PSP’s FIELDS instrument suite. Measurements during PSP Encounters 4−8 revealed pronounced complex shapes in the proton velocity distribution functions (VDFs), in which the tip of the beam undergoes strong perpendicular diffusion, resulting in VDF level contours that resemble a “hammerhead.” We refer to these proton beams, with their attendant “hammerhead” features, as the ion strahl. We present an example of these observations occurring simultaneously with a 7 hr ion-scale wave storm and show results from a preliminary attempt at quantifying the occurrence of ion-strahl broadening through three-component ion VDF fitting. We also provide a possible explanation of the ion perpendicular scattering based on quasilinear theory and the resonant scattering of beam ions by parallel-propagating, right circularly polarized, fast magnetosonic/whistler waves

The Solar Probe ANalyzer - Ions on the Parker Solar Probe

The Solar Probe ANalyzer for Ions (SPAN-I) onboard NASA's Parker Solar Probe spacecraft is an electrostatic analyzer with time-of-flight capabilities that measures the ion composition and three-dimensional distribution function of the thermal corona and solar-wind plasma. SPAN-I measures the energy per charge of ions in the solar wind from 2 eV to 30 keV with a field of view of 247.°5 × 120° while simultaneously separating H+ from He++ to develop 3D velocity distribution functions of individual ion species. These observations, combined with reduced distribution functions measured by the Sun-pointed Solar Probe Cup, will help us further our understanding of the solar-wind acceleration and formation, the heating of the corona, and the acceleration of particles in the inner heliosphere. This paper describes the instrument hardware, including several innovative improvements over previous time-of-flight sensors, the data products generated by the experiment, and the ground calibrations of the sensor. © 2022. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]