The influence of the secondary electrons induced by energetic electrons impacting the Cassini Langmuir probe at Saturn

Garnier, Philippe; Holmberg, M.; Wahlund, Jan‐Erik; Lewis, G. R.; Grimald, S.; Thomsen, M. F.; Gurnett, D. A.; Coates, A. J.; Crary, F. J.; Dandouras, I.

doi:10.1002/2013ja019114

Cited by 11 publications

(10 citation statements)

References 42 publications

(74 reference statements)

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“…This yield is comparable to or even higher than that of the probe used in the laboratory. c. SE emission from the Cassini Langmuir probe due to the bombardment of 250-450 eV energetic electrons has been indicated from its I-V curves on the ion side current for negative probe potentials [Garnier et al, 2012[Garnier et al, , 2013. Depending on the modeling method, the derived δ m is 1.5 to 3.2 at 350 eV, as high as laboratory measurements [He et al, 2004].…”

Section: Discussionmentioning

confidence: 99%

“…Energetic electrons with energy >100 eV are often detected in planetary magnetospheres [Richardson, 1995;Schippers et al, 2008]. The resulting secondary electron (SE) emission is found to be an important charging process for dust grains and space probes [Meyer-Vernet, 1982;Horányi, 1996;Kempf et al, 2006;Ergun et al, 2010;Garnier et al, 2012Garnier et al, , 2013. positive potential [Wahlund et al, 2009;Gustafsson and Wahlund, 2010;Olson et al, 2010].…”

Section: Introductionmentioning

confidence: 99%

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Identification of when a Langmuir probe is in the sheath of a spacecraft: The effects of secondary electron emission from the probe

2015

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Langmuir probes on spacecraft have been used for characterizing the ambient plasma parameters in space. When their boom is short compared to the Debye length, the probes remain immersed in the spacecraft sheath, causing the current-voltage (I-V) characteristics to deviate from that of a probe far away from the spacecraft. We present identification of when a Langmuir probe is in a sheath, based on the secondary electron (SE) emission from the probe itself. The I-V characteristics of a spherical probe are investigated in a plasma sheath above a conducting plate. Plasmas with cold and hot electrons (1 eV and 10 eV), as well as monoenergetic electrons (50-100 eV), are created. The derivative (dI/dV) of the probe I-V curves shows that in addition to a "knee" at a potential more positive than the plasma potential, an additional knee appears at a sheath potential at the probe location. This additional knee is created due to the SE emission from the probe and is identified as an indication of the probe being immersed in the sheath. Our experimental results reproduced the aspects of the Cassini Langmuir probe I-V characteristics, suggesting that at times, the probe may have been immersed in the sheath of the spacecraft in Saturn's magnetosphere, and SE emission from the probe itself may have significantly altered its I-V characteristics.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Identification of when a Langmuir probe is in the sheath of a spacecraft: The effects of secondary electron emission from the probe

2015

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“…Due to solar ultraviolet (UV) radiation and/or hot electron (greater than a few tens of electron volts) bombardment, the photoelectron and/or secondary electron emission from the SC and probe itself can make significant contributions to the probe current and therefore contaminate its I‐V characteristics. The SC and probe emission issue is more severe for in situ measurements close to the Sun where the solar UV flux is high (e.g., Mercury or Venus) or in planetary magnetospheres in which hot electrons often exist (Garnier et al, ). Probe in flowing plasmas …”

Section: Issues Of Current In Situ Langmuir Probesmentioning

confidence: 99%

Development of a Double Hemispherical Probe for Improved Space Plasma Measurements

et al. 2018

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Langmuir probes have been widely used for space plasma measurements for decades. However, there are still challenges in the interpretation of their measurements. Due to the interaction of the ambient plasma with a spacecraft and an onboard probe itself, the local plasma conditions around the probe could be very different from the true ambient plasma of interest. These local plasma conditions are often anisotropic and/or inhomogeneous. Most of the Langmuir probes that are made of a single electrode have difficulties to remove these local plasma effects, introducing errors in the derived plasma characteristics. Directional probes are able to characterize anisotropic and inhomogeneous plasmas. The split Langmuir probe and the Segmented Langmuir Probe have been developed to characterize the plasma flow in the Earth's ionosphere. Here we introduce a new type of a directional Langmuir probe, the Double Hemispherical Probe (DHP), to improve the space plasma measurements in a broad range of scenarios: (a) low‐density plasmas, (b) high surface‐emission (photo and/or secondary electron emission) environments, (c) flowing plasmas, and (d) dust‐rich plasma environments. The DHP consists of two identical hemispheres that are electrically insulated and swept with the same voltages simultaneously. The difference currents between the two hemispheres are used to characterize the anisotropic/inhomogeneous plasma conditions created around the probe, which will be then removed or minimized on the interpretation of their current‐voltage curves. This paper describes the basic concept and design of the DHP sensor, as well as its initial results tested in the laboratory plasma environments.

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“…The LP measurements are also affected by a secondary electron current I se produced by 250 to 450 eV electrons located between 6 and 10 R S , which has been studied in detail by Garnier et al (2012Garnier et al ( , 2013Garnier et al ( , 2014. A significant I se is detected in the sweep as altering the slope b from positive to negative (Garnier et al, 2013;Holmberg et al, 2012). For this reason, no sweep data with b < 0 are included in this study.…”

Section: Rpws Lp Data Reduction Methodsmentioning

confidence: 99%

Density Structures, Dynamics, and Seasonal and Solar Cycle Modulations of Saturn's Inner Plasma Disk

et al. 2017

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We present statistical results from the Cassini Radio and Plasma Wave Science (RPWS) Langmuir probe measurements recorded during the time interval from orbit 3 (1 February 2005) to 237 (29 June 2016). A new and improved data analysis method to obtain ion density from the Cassini LP measurements is used to study the asymmetries and modulations found in the inner plasma disk of Saturn, between 2.5 and 12 Saturn radii (1 RS=60,268 km). The structure of Saturn's plasma disk is mapped, and the plasma density peak, nmax, is shown to be located at ∼4.6 RS and not at the main neutral source region at 3.95 RS. The shift in the location of nmax is due to that the hot electron impact ionization rate peaks at ∼4.6 RS. Cassini RPWS plasma disk measurements show a solar cycle modulation. However, estimates of the change in ion density due to varying EUV flux is not large enough to describe the detected dependency, which implies that an additional mechanism, still unknown, is also affecting the plasma density in the studied region. We also present a dayside/nightside ion density asymmetry, with nightside densities up to a factor of 2 larger than on the dayside. The largest density difference is found in the radial region 4 to 5 RS. The dynamic variation in ion density increases toward Saturn, indicating an internal origin of the large density variability in the plasma disk rather than being caused by an external source origin in the outer magnetosphere.

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The influence of the secondary electrons induced by energetic electrons impacting the Cassini Langmuir probe at Saturn

Cited by 11 publications

References 42 publications

Identification of when a Langmuir probe is in the sheath of a spacecraft: The effects of secondary electron emission from the probe

Identification of when a Langmuir probe is in the sheath of a spacecraft: The effects of secondary electron emission from the probe

Development of a Double Hemispherical Probe for Improved Space Plasma Measurements

Density Structures, Dynamics, and Seasonal and Solar Cycle Modulations of Saturn's Inner Plasma Disk

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