Abstract
Low energy ion measurements in the vicinity of a comet have provided us with important information about the planet’s evolution. The calibration of instruments for thermal ions in the laboratory plays a crucial role when analysing data from in-situ measurements in space. A new low energy ion source based on carbon nanotube electron emitters was developed for calibrating the ion-mode of mass spectrometers or other ion detectors. The electron field emission (FE) properties of carbon nanotubes (CNTs) for H2, He, Ar, O2, and CO2 gases were tested in the experiments. H2, He, Ar, and CO2 adsorbates could change the FE temporarily at pressures from10−6 Pa to10−4 Pa. The FE of CNT remains stable in Ar and increases in H2, but degrades in He, O2, and CO2. All gas adsorbates lead to temporary degradation after working for prolonged periods. The ion current of the ion source is measured by using a Faraday cup and the sensitivity is derived from this measurement. The ion currents for the different gases were around 10 pA (corresponding to 200 ions/cm3 s) and an energy of ~28 eV could be observed.
Highlights
Detection of ions in-situ in the environment of a planetary body plays a crucial role in the investigation of a planet
A calibration facility for solar wind plasma instruments was built using an electron-cyclotron-resonance ion source operating at 2.45 GHz, which could test ions produced from elements ranging from gaseous to solid [4]
A compact ion source was constructed, based on microtips as electron field emitters for calibrating the ion measurement mode of the ROSINA instruments flying in the Rosetta mission [8]
Summary
Detection of ions in-situ in the environment of a planetary body plays a crucial role in the investigation of a planet. A calibration facility for solar wind plasma instruments was built using an electron-cyclotron-resonance ion source operating at 2.45 GHz, which could test ions produced from elements ranging from gaseous to solid [4]. A compact ion source was constructed, based on microtips as electron field emitters for calibrating the ion measurement mode of the ROSINA instruments flying in the Rosetta mission [8]. As an efficient electron field emitter, the carbon nanotube (CNT) is a promising candidate to be applied as a compact ion source because of its reliability and environmental compatibility. [13,14], carbon nanotube devices were thought to be immature for applications as an ion source due to the lack of understanding about the performance of a CNT emitter for different operating gases while it was applied as a standard ion source. The FE current, electron beam stability, and FE reversibility of the CNT emitter were evaluated with different operating gases
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