Parker Solar Probe Observations of Proton Beams Simultaneous with Ion-scale Waves

Abstract

Parker Solar Probe (PSP), NASA's latest and closest mission to the Sun, is on a journey to investigate fundamental enigmas of the inner heliosphere. This paper reports initial observations made by the Solar Probe Analyzer for Ions (SPAN-I), one of the instruments in the Solar Wind Electrons Alphas and Protons (SWEAP) instrument suite. We address the presence of secondary proton beams in concert with ion-scale waves observed by FIELDS, the electromagnetic fields instrument suite. We show two events from PSP's 2 nd orbit that demonstrate signatures consistent with wave-particle interactions. We showcase 3D velocity distribution functions (VDFs) measured by SPAN-I during times of strong wave power at ion-scales. From an initial instability analysis, we infer that the VDFs departed far enough away from local thermodynamic equilibrium (LTE) to provide sufficient free energy to locally generate waves. These events exemplify the types of instabilities that may be present and, as such, may guide future data analysis characterizing and distinguishing between different wave-particle interactions.

Enhanced proton parallel temperature inside patches of switchbacks in the inner heliosphere

“…This combined plasma and magnetic field signature of a patch is the main result of this letter. Overall, T p,⊥ > T p, throughout the interval, which is consistent with many observations of fast wind in the inner heliosphere (Ďurovcová et al 2019;Hellinger et al 2011Hellinger et al , 2013Marsch et al 1981Marsch et al , 1982Marsch et al , 2004Matteini et al 2007;Perrone et al 2019a,b;Stansby et al 2019aStansby et al ,b, 2020 and the recent analysis of slow Alfvénic wind observed by PSP (Huang et al 2020a,b;Verniero et al 2020). In addition, we see in panel (5) that patches sometimes display small density enhancements in both n p and n e .…”

“…Proton VDFs measured by SPAN-Ai often show the presence of both a proton core and a field-aligned beam; a second proton component that streams faster than the core along the direction ofb = B/|B| (see Verniero et al 2020). In Figure 1, we show a typical distribution measured by SPAN-Ai in the instrument frame 1 .…”

“…SPAN-Ai measures particles in a spherical coordinate system: (φ, θ, E), where φ is the azimuthal angle, θ is the elevation angle, and E = 1/2mv 2 is the particle kinetic energy. The instrument has eight angular bins in both φ and θ, with an angular coverage of 247.5 • in azimuth and 120 • in elevation (for more details, see Kasper et al 2016;Livi et al 2020). The instrument is orientated such that the FOV is obstructed by the spacecraft heat-shield, blocking the line-of-sight of the Sunspacecraft line.…”

“…Recently, Woolley et al (2020) identified individual switchbacks with a full 180 • rotation in B to show that the parallel temperature inside the structures is similar to the outside value. Verniero et al (2020) present the first analysis of 3D proton VDFs inside and outside a switchback at 35 solar radii, using 1D fitting to characterise the core and proton beams. They find that the temperature of both components remained unchanged through the field reversal.…”

Constraining Ion-Scale Heating and Spectral Energy Transfer in Observations of Plasma Turbulence

“…Correlations between signatures of the transition range and parameters associated with stochastic heating were not found [42,63]. Measurements of 3D ion distributions will enable comparison of damping rates associated with, e.g., Landau and cyclotron resonance, with our observed dissipation rates [1,8,[10][11][12][13][14]17,18,76,82,83]. Additionally, heating processes may leave clear signatures in the distribution function: e.g., diffusive shells in the case of cyclotron resonance [84] or flattening associated with resonant damping or perpendicular stochastic heating [63,85].…”