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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
Author(s) -
Wang X.,
Hsu H.W.,
Horányi M.
Publication year - 2015
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2014ja020624
Subject(s) - langmuir probe , debye length , plasma , debye sheath , spacecraft , electron , atomic physics , physics , plasma diagnostics , secondary emission , astronomy , quantum mechanics
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.