Cluster PEACE observations of electrons of spacecraft origin

Abstract. The two PEACE (Plasma Electron And Current Experiment) sensors on board each Cluster spacecraft sample the electron velocity distribution across the full 4<pi> solid angle and the energy range 0.7 eV to 26 keV with a time resolution of 4 s. We present high energy and angular resolution 3D observations of electrons of spacecraft origin in the various environments encountered by the Cluster constellation, including a lunar eclipse interval where the spacecraft potential was reduced but remained positive, and periods of ASPOC (Active Spacecraft POtential Control) operation which reduced the spacecraft potential. We demonstrate how the spacecraft potential may be found from a gradient change in the PEACE low energy spectrum, and show how the observed spacecraft electrons are confined by the spacecraft potential. We identify an intense component of the spacecraft electrons with energies equivalent to the spacecraft potential, the arrival direction of which is seen to change when ASPOC is switched on. Another spacecraft electron component, observed in the sunward direction, is reduced in the eclipse but unaffected by ASPOC, and we believe this component is produced in the analyser by solar UV. We find that PEACE anodes with a look direction along the spacecraft surfaces are more susceptible to spacecraft electron contamination than those which look perpendicular to the surface, which justifies the decision to mount PEACE with its field-of-view radially outward rather than tangentially.Key words. Magnetosheric physics (general or miscellaneous) Space plasma physics (spacecraft sheaths, wakes, charging)

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Observations of low energy ions around the diamagnetic cavity at comet 67P

10.5194/egusphere-egu2020-8318 ◽

2020 ◽

Author(s):

Gabriella Stenberg Wieser ◽

Martin Wieser ◽

Sofia Bergman ◽

Elias Odelstad ◽

Fredrik Johansson ◽

...

Keyword(s):

Ion Flux ◽

Low Energy ◽

Electron Velocity ◽

Ion Dynamics ◽

Ion Temperature ◽

Electron Velocity Distribution ◽

Spacecraft Potential ◽

Sudden Decrease ◽

Low Energy Ions ◽

Comet 67P

<p>We investigate the variations in low energy cometary ions around comet 67P. Detailed measurements of these ions were made possible by implementing a new instrumental mode of the ion mass spectrometer on the Rosetta spacecraft. The nominal time resolution was increased from 192 s to 4 s at the expense of the energy range and the field-of-view.</p><p>In this study we focus on ion observations made outside of, but in the vicinity of, the diamagnetic cavity. The ion dynamics here is clearly linked to variations of the magnetic field strength and properties of the electron velocity distribution, manifested by the spacecraft potential. Preliminary results show that the ion flux correlates with the changes of the spacecraft potential. The maximum ion flux is, however, observed about 20 seconds after a sudden decrease of the potential (corresponding to an increase in electron density if electron temperature is constant). We also find evidence of small ion temperature increases both when the spacecraft potential changes fast and at the time of maximum ion flux.</p>

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Interaction of suprathermal solar wind electron fluxes with sheared whistler waves: fan instability

Annales Geophysicae ◽

10.5194/angeo-21-1393-2003 ◽

2003 ◽

Vol 21 (7) ◽

pp. 1393-1403 ◽

Cited By ~ 16

Author(s):

C. Krafft ◽

A. Volokitin

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Energetic Electron ◽

High Energy ◽

Electron Velocity ◽

Lower Hybrid ◽

Whistler Waves ◽

Electron Velocity Distribution ◽

Radio Science ◽

Ambient Magnetic Field

Abstract. Several in situ measurements performed in the solar wind evidenced that solar type III radio bursts were some-times associated with locally excited Langmuir waves, high-energy electron fluxes and low-frequency electrostatic and electromagnetic waves; moreover, in some cases, the simultaneous identification of energetic electron fluxes, Langmuir and whistler waves was performed. This paper shows how whistlers can be excited in the disturbed solar wind through the so-called "fan instability" by interacting with energetic electrons at the anomalous Doppler resonance. This instability process, which is driven by the anisotropy in the energetic electron velocity distribution along the ambient magnetic field, does not require any positive slope in the suprathermal electron tail and thus can account for physical situations where plateaued reduced electron velocity distributions were observed in solar wind plasmas in association with Langmuir and whistler waves. Owing to linear calculations of growth rates, we show that for disturbed solar wind conditions (that is, when suprathermal particle fluxes propagate along the ambient magnetic field), the fan instability can excite VLF waves (whistlers and lower hybrid waves) with characteristics close to those observed in space experiments.Key words. Space plasma physics (waves and instabilities) – Radio Science (waves in plasma) – Solar physics, astrophysics and astronomy (radio emissions)

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Electron velocity distribution and lion roars in the magnetosheath

Annales Geophysicae ◽

10.5194/angeo-24-1725-2006 ◽

2006 ◽

Vol 24 (6) ◽

pp. 1725-1735 ◽

Cited By ~ 43

Author(s):

W. Masood ◽

S. J. Schwartz ◽

M. Maksimovic ◽

A. N. Fazakerley

Keyword(s):

Velocity Distribution ◽

Velocity Distribution Function ◽

Temporal Analysis ◽

Plasma Electron ◽

Electron Velocity ◽

Theoretical Expression ◽

Temperature Anisotropy ◽

Electron Velocity Distribution ◽

Electron Velocity Distribution Function ◽

Spatio Temporal

Abstract. Whistler waves which are termed "lion roars" in the magnetosheath are studied using data obtained by the Spectrum Analyser (SA) of the Spatio-Temporal Analysis of Field Fluctuations (STAFF) experiment aboard Cluster. Kinetic theory is then employed to obtain the theoretical expression for the whistler wave with electron temperature anisotropy which is believed to trigger lion roars in the magnetosheath. This allows us to compare theory and data. This paper for the first time studies the details of the electron velocity distribution function as measured by the Plasma Electron And Current Experiment (PEACE) in order to investigate the underlying causes for the different types of lion roars found in the data. Our results show that while some instances of lion roars could be locally generated, the source of others must be more remote regions of the magnetosheath.

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Absence of the strahl during times of slow wind

Annales Geophysicae ◽

10.5194/angeo-35-71-2017 ◽

2017 ◽

Vol 35 (1) ◽

pp. 71-85 ◽

Cited By ~ 7

Author(s):

Chris Gurgiolo ◽

Melvyn L. Goldstein

Keyword(s):

Solar Wind ◽

Solar Wind Speed ◽

Velocity Distribution Function ◽

Plasma Electron ◽

Electron Velocity ◽

Electron Velocity Distribution ◽

Electron Velocity Distribution Function ◽

Slow Wind ◽

Cluster 2 ◽

Statistical Noise

Abstract. It is not uncommon during periods when the solar wind speed is less than 425 km s−1 to observe near 1 AU no evidence of a strahl population in either the electron solar wind or within the foreshock. Estimating the fluid flow within each energy step returned from the Plasma Electron And Current Experiment (PEACE) on board Cluster-2 often finds that in slow wind the GSE spherical flow angles in energies above where there is a clear core/halo signature are often close to radial with no evidence of a field-aligned flow. This signifies the lack of a strahl presence in the electron velocity distribution function (eVDF). When there is no obvious strahl signature in the data, the electrons above the core/halo in energy appear to be unstructured and smeared in angle. This can either be interpreted as due to statistical noise in low counting rate situations or the result of intense scattering. Regions where the strahl is seen and not seen are often separated by a very thin boundary layer. These transitions in the spacecraft frame of reference can be quite rapid, generally occurring within one to two spins (4–8 s).

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Active spacecraft potential control for Cluster – implementation and first results

Annales Geophysicae ◽

10.5194/angeo-19-1289-2001 ◽

2001 ◽

Vol 19 (10/12) ◽

pp. 1289-1302 ◽

Cited By ~ 76

Author(s):

K. Torkar ◽

W. Riedler ◽

C. P. Escoubet ◽

M. Fehringer ◽

R. Schmidt ◽

...

Keyword(s):

Metal Ion ◽

Plasma Electron ◽

Ion Source ◽

Equilibrium Potential ◽

Potential Control ◽

Source Type ◽

Spacecraft Potential ◽

Electrons And Ions ◽

Electrostatic Charging ◽

First Results

Abstract. Electrostatic charging of a spacecraft modifies the distribution of electrons and ions before the particles enter the sensors mounted on the spacecraft body. The floating potential of magnetospheric satellites in sunlight very often reaches several tens of volts, making measurements of the cold (several eV) component of the ambient ions impossible. The plasma electron data become contaminated by large fluxes of photoelectrons attracted back into the sensors. The Cluster spacecraft are equipped with emitters of the liquid metal ion source type, producing indium ions at 5 to 9 keV energy at currents of some tens of microampere. This current shifts the equilibrium potential of the spacecraft to moderately positive values. The design and principles of the operation of the instrument for active spacecraft potential control (ASPOC) are presented in detail. Experience with spacecraft potential control from the commissioning phase and the first two months of the operational phase are now available. The instrument is operated with constant ion current for most of the time, but tests have been carried out with varying currents and a "feedback" mode with the instrument EFW, which measures the spacecraft potential . That has been reduced to values according to expectations. In addition, the low energy electron measurements show substantially reduced fluxes of photoelectrons as expected. The flux decrease in photoelectrons returning to the spacecraft, however, occurs at the expense of an enlarged sheath around the spacecraft which causes problems for boom-mounted probes.Key words. Space plasma physics (spacecraft sheaths, wakes, charging); Instruments and techniques; Active perturbation experiments

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