Abstract
Electrostatic analysers measure the flux of plasma particles in velocity space and determine their velocity distribution function. There are occasions when science objectives require high time-resolution measurements, and the instrument operates in short measurement cycles, sampling only a portion of the velocity distribution function. One such high-resolution measurement strategy consists of sampling the two-dimensional pitch-angle distributions of the plasma particles, which describes the velocities of the particles with respect to the local magnetic field direction. Here, we investigate the accuracy of plasma bulk parameters from such high-resolution measurements. We simulate electron observations from the Solar Wind Analyserâs (SWA) Electron Analyser System (EAS) on board Solar Orbiter. We show that fitting analysis of the synthetic datasets determines the plasma temperature and kappa index of the distribution within 10% of their actual values, even at large heliocentric distances where the expected solar wind flux is very low. Interestingly, we show that although measurement points with zero counts are not statistically significant, they provide information about the particle distribution function which becomes important when the particle flux is low. We also examine the convergence of the fitting algorithm for expected plasma conditions and discuss the sources of statistical and systematic uncertainties.
Highlights
The environment of interplanetary space is filled with a very low-density plasma, primarily consisting of electrons and protons with a small component of heavier ions. Investigations of this plasma measure the flux of particles in energy and angle to determine the velocity distribution function (VDF) of different particle species
We model the expected measurements of solar wind plasma electrons, considering the instrumentâs ideal response, based on the initial instrument calibration
The>accuracy of the derived the plasma parameters when measurement points with zero counts (Ci = 0) are excluded the parameters is a function of the flux of plasma particles
Summary
The environment of interplanetary space is filled with a very low-density plasma, primarily consisting of electrons and protons with a small component of heavier ions. Investigations of this plasma measure the flux of particles in energy and angle to determine the velocity distribution function (VDF) of different particle species. The VDF indicates how energy is distributed between particles of the same type, and can be analysed to provide bulk properties of the plasma such as density, velocity, and temperature. The velocities of space plasma particles often follow kappa distribution functions A large number of studies have determined kappa distribution functions in space plasma environments, such as the solar wind (see, e.g., in [10,11,12,13,14,15]), planetary magnetospheres
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