Core Electron Heating By Triggered Ion Acoustic Waves In The Solar Wind

TL;DR

This study shows that triggered ion acoustic waves in the solar wind can significantly heat core electrons, with the effect observed at specific distances and wave frequencies, revealing a key mechanism for electron heating in the solar wind.

Contribution

It demonstrates that triggered ion acoustic waves are the primary cause of electron core heating in the solar wind between 15 and 30 solar radii, a novel insight into solar wind plasma dynamics.

Findings

Triggered ion acoustic waves cause up to twofold electron heating.

Electron temperature at 15 solar radii is approximately 55 eV.

Ion acoustic waves dominate at frequencies >100 Hz between 15-30 solar radii.

Abstract

Perihelion passes on Parker Solar Probe orbits six through nine have been studied to show that solar wind core electrons emerged from 15 solar radii with a temperature of 55 plus or minus 5 eV, independent of the solar wind speed which varied from 300 to 800 km/sec. After leaving 15 solar radii and in the absence of triggered ion acoustic waves at greater distances, the core electron temperature varied with radial distance, R, in solar radii, as 1900R-4/3 electron volts because of cooling produced by the adiabatic expansion. The coefficient, 1900, reproduces the minimum core electron perpendicular temperature observed during the 25 days of observation. In the presence of triggered ion acoustic waves, the core electrons were isotropically heated as much as a factor of two above the minimum temperature, 1900R-4/3 eV. Triggered ion acoustic waves were the only waves observed in coincidence with the electron core heating. They are the dominant wave mode at frequencies greater than 100 Hz at solar distances between 15 and 30 solar radii.