On the temperature anisotropy of the core part of the proton velocity distribution function in the solar wind

2004 ◽  
Vol 109 (A4) ◽  
Author(s):  
E. Marsch
Keyword(s):  
Solar Wind ◽  
Distribution Function ◽  
Velocity Distribution ◽  
Velocity Distribution Function ◽  
Temperature Anisotropy ◽  
The Core ◽  
Core Part

scholarly journals Determining the Bulk Parameters of Plasma Electrons from Pitch-Angle Distribution Measurements

Entropy ◽  
2020 ◽  
Vol 22 (1) ◽  
pp. 103 ◽  
Author(s):  
Georgios Nicolaou ◽  
Robert Wicks ◽  
George Livadiotis ◽  
Daniel Verscharen ◽  
Christopher Owen ◽  
...  
Keyword(s):  
Solar Wind ◽  
Distribution Function ◽  
High Resolution ◽  
Velocity Distribution ◽  
Pitch Angle ◽  
Velocity Distribution Function ◽  
Local Magnetic Field ◽  
Magnetic Field Direction ◽  
Angle Distribution ◽  
Bulk Parameters

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 Analyser’s (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.

scholarly journals Apparent temperature anisotropies due to wave activity in the solar wind

2011 ◽  
Vol 29 (5) ◽  
pp. 909-917 ◽  
Author(s):  
D. Verscharen ◽  
E. Marsch
Keyword(s):  
Solar Wind ◽  
Distribution Function ◽  
Collisionless Plasma ◽  
Velocity Distribution Function ◽  
Wave Activity ◽  
Apparent Temperature ◽  
Time Averaging ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Underlying Distribution

Abstract. The fast solar wind is a collisionless plasma permeated by plasma waves on many different scales. A plasma wave represents the natural interplay between the periodic changes of the electromagnetic field and the associated coherent motions of the plasma particles. In this paper, a model velocity distribution function is derived for a plasma in a single, coherent, large-amplitude wave. This model allows one to study the kinetic effects of wave motions on particle distributions. They are by in-situ spacecraft measured by counting, over a certain sampling time, the particles coming from various directions and having different energies. We compare our results with the measurements by the Helios spacecraft, and thus find that by assuming high wave activity we are able to explain key observed features of the measured distributions within the framework of our model. We also address the recent discussions on nonresonant wave–particle interactions and apparent heating. The applied time-averaging procedure leads to an apparent ion temperature anisotropy which is connected but not identical to the intrinsic temperature of the underlying distribution function.

Possible instrumental effects on moments computation of the solar wind proton velocity distribution function: Helios observations

2020 ◽  
Vol 639 ◽  
pp. A82 ◽  
Author(s):  
R. De Marco ◽  
R. Bruno ◽  
R. D’Amicis ◽  
D. Telloni ◽  
D. Perrone
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Distribution Function ◽  
Velocity Distribution ◽  
Field Data ◽  
Velocity Distribution Function ◽  
Instrumental Effects ◽  
Solar Wind Proton ◽  
Magnetic Field Data ◽  
Density Values

The solar wind is a highly turbulent medium in which most of the energy is carried by Alfvénic fluctuations. These fluctuations have a wide range of scales whose high-frequency tail can be relevant for the sampling techniques commonly used to detect the particle distribution in phase space in situ. We analyze the effect of Alfvénic fluctuations on moments computation of the solar wind proton velocity distribution for a plasma sensor, whose sampling time is comparable or even longer than the typical timescale of the velocity fluctuations induced by these perturbations. In particular, we numerically simulated the sampling procedure used on board Helios 2. We directly employed magnetic field data recorded by the Helios 2 magnetometer, when the s/c was immersed in fast wind during its primary mission to the Sun, to simulate Alfvénic fluctuations. More specifically, we used magnetic field data whose cadence of 4 Hz is considerably higher than that the plasma sensor needed to sample a full velocity distribution function, and we average these data to 1 Hz, which is the spin period of Helios. Density values, which are necessary to build Alfvénic fluctuations at these scales, are not available because the cadence of the Helios plasma data is 40.5 s. The adopted solution is based on the assumption that the available Helios plasma density power spectrum can be extended to the same frequencies as the magnetic field spectrum by extrapolating the power-law fit of the low-frequency range to the frequencies relevant for this study. Surrogate density values in the time domain are then obtained by inverse transforming this spectrum. We show that it cannot be excluded that relevant instrumental effects strongly contribute to generate interesting spectral and kinetic features that have been interpreted in the past literature as exclusively due to physical mechanisms.

scholarly journals Velocity distribution function of hydrogen atoms in ion source discharges

2021 ◽  
Author(s):  
Tatsuhiro Tokai ◽  
Yuji Shimabukuro ◽  
Hidenori Takahashi ◽  
Keita Bito ◽  
Motoi Wada
Keyword(s):  
Distribution Function ◽  
Velocity Distribution ◽  
Velocity Distribution Function ◽  
Ion Source ◽  
Hydrogen Atoms

scholarly journals Velocity distribution function of spontaneously evaporating atoms

2020 ◽  
Vol 5 (10) ◽  
Author(s):  
Sergiu Busuioc ◽  
Livio Gibelli ◽  
Duncan A. Lockerby ◽  
James E. Sprittles
Keyword(s):  
Distribution Function ◽  
Velocity Distribution ◽  
Velocity Distribution Function
Sign in / Sign up

Export Citation Format

Share Document