In this Paper, we present the first results from the Flux Angle operation mode of the Faraday Cup instrument onboard Parker Solar Probe. The Flux Angle mode allows rapid measurements of phase space density fluctuations close to the peak of the proton velocity distribution function with a cadence of 293 Hz. This approach provides an invaluable tool for understanding kinetic scale turbulence in the solar wind and solar corona. We describe a technique to convert the phase space density fluctuations into vector velocity components and compute several turbulence parameters such as spectral index, residual energy and cross helicity during two intervals the Flux Angle mode was used in Parker Solar Probe's first encounter at 0.174 AU distance from the Sun.

Daniel Vech Justin C. Kasper Kristopher G. Klein Jia Huang Michael L. Stevens Christopher H. K. Chen Anthony W. Case Kelly Korreck Stuart D. Bale Trevor A. Bowen Phyllis L. Whittlesey Roberto Livi Davin E. Larson David Malaspina Marc Pulupa John Bonnell Peter Harvey Keith Goetz Thierry Dudok de Wit Robert MacDowall

A tutorial is presented which demonstrates the theory and usage of the Parker-Sochacki method of numerically solving systems of differential equations. Solutions are demonstrated for the case of projectile motion in air, and for the classical Newtonian N-body problem with mutual gravitational attraction.

Joseph W. Rudmin

Parker Solar Probe (PSP) data recorded within a heliocentric radial distance of 0.3 AU have revealed a magnetic field dominated by Alfv\'enic structures that undergo large local variations or even reversals of the radial magnetic field. They are called magnetic switchbacks, they are consistent with folds in magnetic field lines within a same magnetic sector, and are associated with velocity spikes during an otherwise calmer background. They are thought to originate either in the low solar atmosphere through magnetic reconnection processes, or result from the evolution of turbulence or velocity shears in the expanding solar wind. In this work, we investigate the temporal and spatial characteristic scales of magnetic switchback patches. We define switchbacks as a deviation from the nominal Parker spiral direction and detect them automatically for PSP encounters 1, 2, 4 and 5. We focus in particular on a 5.1-day interval dominated by switchbacks during E5. We perform a wavelet transform of the solid angle between the magnetic field and the Parker spiral and find periodic spatial modulations with two distinct wavelengths, respectively consistent with solar granulation and supergranulation scales. In addition we find that switchback occurrence and spectral properties seem to depend on the source region of the solar wind rather than on the radial distance of PSP. These results suggest that switchbacks are formed in the low corona and modulated by the solar surface convection pattern.

Naïs Fargette Benoit Lavraud Alexis Rouillard Victor Réville Thierry Dudok De Wit Clara Froment Jasper S. Halekas Tai Phan David Malaspina Stuart D. Bale Justin Kasper Philippe Louarn Anthony W. Case Kelly E. Korreck Davin E. Larson Marc Pulupa Michael L. Stevens Phyllis L. Whittlesey Matthieu Berthomier

Heat transport in the solar corona and wind is still a major unsolved astrophysical problem. Because of the key role played by electrons, the electron density and temperature(s) are important prerequisites for understanding these plasmas. We present such in situ measurements along the two first solar encounters of Parker Solar Probe (PSP), between 0.5 and 0.17 AU from the Sun, revealing different states of the emerging solar wind near solar activity minimum. These preliminary results are obtained from a simplified analysis of the plasma quasi-thermal noise (QTN) spectrum measured by the Radio Frequency Spectrometer (RFS/FIELDS). The local electron density is deduced from the tracking of the plasma line, which enables accurate measurements, independent of calibrations and spacecraft perturbations, whereas the temperatures of the thermal and supra-thermal components of the velocity distribution, as well as the average kinetic temperature are deduced from the shape of the plasma line. The temperature of the weakly collisional thermal population, similar for both encounters, decreases with distance as $R^{-0.74}$, much slower than adiabatic. In contrast, the temperature of the nearly collisionless suprathermal population exhibits a virtually flat radial variation. The 7-second resolution of the density measurements enables us to deduce the low-frequency spectrum of compressive fluctuations around perihelion, varying as $f^{-1.4}$. This is the first time that QTN spectroscopy is implemented with an electric antenna length not exceeding the plasma Debye length. As PSP will approach the Sun, the decrease in Debye length is expected to considerably improve the accuracy of the temperature measurements.

Michel Moncuquet Nicole Meyer-Vernet Karine Issautier Marc Pulupa J. W. Bonnell Stuart D. Bale Thierry Dudok de Wit Keith Goetz Léa Griton Peter R. Harvey Robert J. MacDowall Milan Maksimovic David M. Malaspina

Scaling relations are one of the hallmarks of nodal superconductivity since they contain information characteristic for gapless order parameters. In this paper we derive the scaling relations for the thermodynamics and the thermal conductivity in the vortex state of the A and B phases of the skutterudite PrOs4Sb12. Experimental confirmation of these scaling relations can provide further support for anisotropic gap functions which were previously considered for this material.

H. Won S. Haas D. Parker K. Maki

In contrast to multigap superconductors (e.g. MgB$_{2}$), the low-temperature properties of nodal superconductors are dominated by nodal excitations. Here we extend for a variety of nodal superocnductors the earlier work by Simon and Lee and K\"ubert and Hirschfeld. The scaling relations seen in the thermodynamics and the thermal conductivity will provide an unequivocal test of nodal superconductivity.

K. Maki D. Parker H. Won

The shape of the electron velocity distribution function plays an important role in the dynamics of the solar wind acceleration. Electrons are normally modelled with three components, the core, the halo, and the strahl. We investigate how well the fast strahl electrons in the inner heliosphere preserve the information about the coronal electron temperature at their origin. We analysed the data obtained by two missions, Helios spanning the distances between 65 and 215 R$_S$, and Parker Solar Probe (PSP) reaching down to 35 R$_S$ during its first two orbits around the Sun. The electron strahl was characterised with two parameters, pitch-angle width (PAW), and the strahl parallel temperature (T$_{s\parallel}$). PSP observations confirm the already reported dependence of strahl PAW on core parallel plasma beta ($\beta_{ec\parallel}$)\citep{Bercic2019}. Most of the strahl measured by PSP appear narrow with PAW reaching down to 30$^o$. The portion of the strahl velocity distribution function aligned with the magnetic field is for the measured energy range well described by a Maxwellian distribution function. T$_{s\parallel}$ was found to be anti-correlated with the solar wind velocity, and independent of radial distance. These observations imply that T$_{s\parallel}$ carries the information about the coronal electron temperature. The obtained values are in agreement with coronal temperatures measured using spectroscopy (David et al. 2998), and the inferred solar wind source regions during the first orbit of PSP agree with the predictions using a PFSS model (Bale et al. 2019, Badman et al. 2019).

Laura Bercic Davin Larson Phyllis Whittlesey Milan Maksimovic Samuel T. Badman Simone Landi Lorenzo Matteini Stuart. D. Bale John W. Bonnell Anthony W. Case Thierry Dudok de Wit Keith Goetz Peter R. Harvey Justin C. Kasper Kelly E. Korreck Roberto Livi Robert J. MacDowall David M. Malaspina Marc Pulupa Michael L. Stevens

Direct evidence of an inertial-range turbulent energy cascade has been provided by spacecraft observations in heliospheric plasmas. In the solar wind, the average value of the derived heating rate near 1 au is $\sim 10^{3}\, \mathrm{J\,kg^{-1}\,s^{-1}}$, an amount sufficient to account for observed departures from adiabatic expansion. Parker Solar Probe (PSP), even during its first solar encounter, offers the first opportunity to compute, in a similar fashion, a fluid-scale energy decay rate, much closer to the solar corona than any prior in-situ observations. Using the Politano-Pouquet third-order law and the von K\'arm\'an decay law, we estimate the fluid-range energy transfer rate in the inner heliosphere, at heliocentric distance $R$ ranging from $54\,R_{\odot}$ (0.25 au) to $36\,R_{\odot}$ (0.17 au). The energy transfer rate obtained near the first perihelion is about 100 times higher than the average value at 1 au. This dramatic increase in the heating rate is unprecedented in previous solar wind observations, including those from Helios, and the values are close to those obtained in the shocked plasma inside the terrestrial magnetosheath.

Riddhi Bandyopadhyay M. L. Goldstein B. A. Maruca W. H. Matthaeus T. N. Parashar D. Ruffolo R. Chhiber A. Usmanov A. Chasapis R. Qudsi Stuart D. Bale J. W. Bonnell Thierry Dudok de Wit Keith Goetz Peter R. Harvey Robert J. MacDowall David M. Malaspina Marc Pulupa J. C. Kasper K. E. Korreck A. W. Case M. Stevens P. Whittlesey D. Larson R. Livi K. G. Klein M. Velli N. Raouafi

We investigate the thermoelectric properties of ${\beta}$-FeSi$_{\text2}$ using first principles electronic structure and Boltzmann transport calculations. We report a high thermopower for both \textit{p}- and \textit{n}-type ${\beta}$-FeSi$_{\text2}$ over a wide range of carrier concentration and in addition find the performance for \textit{n}-type to be higher than for the \textit{p}-type. Our results indicate that, depending upon temperature, a doping level of 3$\times10{^{20}}$ - 2$\times10{^{21}}$ cm${^{-3}}$ may optimize the thermoelectric performance.

Tribhuwan Pandey David J. Singh David Parker Abhishek K. Singh

Thermoelectric performance is of interest for numerous applications such as waste heat recovery and solid state energy conversion, and will be seen to be closely connected to topological insulator behavior. In this context we here report first principles transport and defect calculations for Bi$_{2}$Te$_{2}$Se in relation to Bi$_{2}$Te$_{3}$. The two compounds are found to contain remarkably different electronic structures in spite of being isostructural and isoelectronic. We discuss these results in terms of the topological insulator characteristics of these compounds.

Hongliang Shi David Parker Mao-Hua Du David J. Singh