Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
On the interpretation of Langmuir probe data inside a spacecraft sheath
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
Swedish Institute of Space Physics, Uppsala.
Belgian Insitute for Space Aeronomy, Brussels, Belgium.
2010 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 81, no 10, 105106-1-105106-8 p.Article in journal (Refereed) Published
Abstract [en]

If a Langmuir probe is located inside the sheath of a negatively charged spacecraft, there is a risk that the probe characteristic is modified compared to that of a free probe in the ambient plasma. We have studied this probe-in-spacecraft-sheath problem in the parameter range of a small Langmuir probe (with radius r(LP)<<lambda(D)) using a modified version of the orbit motion limited (OML) probe theory. We find that the ambient electron contribution I-e(U-LP) to the probe characteristic is suitably analyzed in terms of three regions of applied probe potential U-LP. In region I, where the probe is negatively charged (i.e., U-LP<U-1, where U-1 is the potential in the sheath at the probe position), the probe characteristic I-e(U-LP) is close to that of OML theory for a free probe in the ambient plasma. In the probe potential range U-LP>U-1, there is first a transition region II in applied potential, U-1<U-LP<U-2, in which the key factor to determine the shape of I-e(U-LP) is a potential minimum U-M between the probe and the ambient plasma. This minimum gives the depth U-pl-U-M of a potential barrier that prevents the lowest energy ambient electrons from reaching the probe. For a high enough positive probe potential, in region III, the barrier becomes small. Here, I-e(U-LP) again approaches OML theory for a free probe. The boundary U-2 between regions II and III is somewhat arbitrary; we propose a condition on the barrier, U-pl-U-M << k(B)T(e)/e, as the definition of region III. The main findings in this work are qualitative rather than quantitative. The existence of the transition region points to that special care must be taken to extract plasma parameters from measured I(U-LP) as the probe characteristic is likely to depart from usual OML in crucial respects: (1) the ambient plasma potential U-pl falls into the transition region, but there is no obvious knee or other feature to identify it, (2) there is in this region no exponential part of I-e(U-LP) that can be used to obtain T-e, instead, (3) the probe size is important in determining the curve shape. We have tentatively applied our simplified probe-in-sheath model to real probe data from the Cassini spacecraft, taken in the dense plasma of Saturn's magnetosphere. We propose that our model gives a better description than OML of measured Langmuir probe sweeps in space plasmas where the Langmuir probe is situated within the spacecraft sheath, i.e., for long Debye lengths. The understanding of these probe sweep effects in such regions may improve by self-consistent particle simulations of the spacecraft environment.

Place, publisher, year, edition, pages
2010. Vol. 81, no 10, 105106-1-105106-8 p.
Keyword [en]
Ambient plasmas, Applied potentials, Cassini spacecraft, Curve shape, Debye length, Dense plasma, Key factors, OML theory, Parameter range, Particle simulations, Plasma parameter, Potential barriers, Potential minima, Potential range, Probe characteristics, Probe position, Probe size, Sheath problem, Space plasmas, Transition regions, Langmuir probes, Magnetosphere, Plasmas, Spacecraft
National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-12939DOI: 10.1063/1.3482155ISI: 000283753400050Scopus ID: 2-s2.0-78149444107OAI: oai:DiVA.org:kth-12939DiVA: diva2:319766
Note
QC 20100519. Uppdaterad från submitted till published (20101213).Available from: 2010-05-19 Created: 2010-05-19 Last updated: 2012-05-07Bibliographically approved
In thesis
1. Object-plasma interaction in the vicinity of Enceladus
Open this publication in new window or tab >>Object-plasma interaction in the vicinity of Enceladus
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

    The Cassini spacecraft orbits Saturn since 2004, carrying a multitude of instruments for studies of the plasma environment around the planet as well as the constituents of the ring system. Of particular interest to the present thesis is the large E ring, which consists mainly of water ice grains, smaller than a few micrometres, referred to as dust. The work presented here is concerned with the interaction between, on the one hand, the plasma and, on the other hand, the dust, the spacecraft and the Langmuir probe carried by it. In Paper I, dust densities along the trajectory of Cassini, as it passes through the ring, are inferred from measured electron and ion densities. In Paper II, the situation where a Langmuir probe is located in the potential well of a spacecraft is considered. The importance of knowing the potential structure around the spacecraft and probe is emphasised and its effect on the probe’s current-voltage characteristic is illustrated with a simple analytical model. In Paper III, particle-in-cell simulations are employed to study the potential and density profiles around the Cassini as it travels through the plasma at the orbit of the moon Enceladus.

Abstract [sv]

   Rymdsonden Cassini befinner sig i omloppsbana kring Saturnus sedan 2004 och bär med sig en mångfald av instrument för att studera plasmat och ringarna som omger planeten. Av särskilt intresse i denna licentiatuppsats är den stora E-ringen. Denna utgörs huvudsakligen av mikrometerstora (eller mindre) dammpartiklar, bestående av is. Det arbete som presenteras här behandlar interaktion mellan, å ena sidan, plasmat och, å andra sidan, dammet, rymdsonden och Langmuirprob som denna är utrustad med. I den bilagda Paper I utvinns dammtätheter längs Cassinis bana genom E-ringen ur mätta elektron- och jontätheter. I Paper II betraktas situationen där en Langmuirprob befinner sig i potentialgropen som omger en rymdsond. Här betonas vikten av att ta hänsyn till potentialstrukturen kring rymdsond och prob, och en enkel analytisk modell används för att illustrera hur probens ström-spänningskaraktäristik kan påverkas av denna potentialstruktur. I Paper III studeras täthets- och potentialprofilerna runt Cassini numeriskt med particle-in-cellsimuleringar för parametrar som modellerar hur rymdsonden rör sig relativt plasmat vid månen Enceladus bana.

 

Publisher
xi, 34 p.
Series
Trita-EE, ISSN 1653-5146
Identifiers
urn:nbn:se:kth:diva-12941 (URN)978-91-7415-673-7 (ISBN)
Presentation
2010-06-04, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100519Available from: 2010-05-19 Created: 2010-05-19 Last updated: 2012-03-21Bibliographically approved
2. Plasma and dust interaction in the magnetosphere of Saturn
Open this publication in new window or tab >>Plasma and dust interaction in the magnetosphere of Saturn
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Cassini spacecraft orbits Saturn since 2004, carrying a multitude of instruments for studies of the plasma environment around the planet as well as the constituents of the ring system. Of particular interest to the present thesis is the large E ring, which consists mainly of water ice grains, smaller than a few micrometres, referred to as dust. The first part of the work presented here is concerned with the interaction between, on the one hand, the plasma and, on the other hand, the dust, the spacecraft and the Langmuir probe carried by the spacecraft. In Paper I, dust densities along the trajectory of Cassini, as it passes through the ring, are inferred from measured electron and ion densities. In Paper II, the situation where a Langmuir probe is located in the potential well of a spacecraft is considered. The importance of knowing the potential structure around the spacecraft and probe is emphasised and its effect on the probe's current-voltage characteristic is illustrated with a simple analytical model. In Paper III, particle-in-cell simulations are employed to study the potential and density profiles around the Cassini as it travels through the plasma at the orbit of the moon Enceladus. The latter part of the work concerns large-scale currents and convection patterns. In Paper IV, the effects of charged E-ring dust moving across the magnetic field is studied, for example in terms of what field-aligned currents it sets up, which compared to corresponding plasma currents. In Paper V, a model for the convection of the magnetospheric plasma is proposed that recreates the co-rotating density asymmetry of the plasma.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xiii, 40 p.
Series
Trita-EE, ISSN 1653-5146 ; 2012:018
Keyword
saturn, dusty plasma
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-93983 (URN)978-91-7501-343-5 (ISBN)
Public defence
2012-05-28, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20120507Available from: 2012-05-07 Created: 2012-05-03 Last updated: 2012-05-07Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textScopus

Search in DiVA

By author/editor
Olson, JonasBrenning, Nils
By organisation
Space and Plasma Physics
In the same journal
Review of Scientific Instruments
Astronomy, Astrophysics and CosmologyFusion, Plasma and Space Physics

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 87 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf