3:00 PM - 3:15 PM
[PCG20-18] Development of a Compact Mass Spectrometer Capable of Separating and Quantifying CNO Ions
Keywords:Planetary Exploration, Equipment Development, Mass Spectrometer
Understanding the atmospheric composition of planets and small celestial bodies is crucial for comprehending their environment, evolution, and formation processes. For example, it is known that nitrogen and oxygen are escaping from the Earth's ionosphere, and investigating their composition ratios and dependence on solar activity provides insights into the atmospheric evolution of Earth and, by extension, other planets. However, the traditional Time-of-Flight (TOF) mass spectrometers, which have been used in the past, have a mass resolution of less than 10, making it difficult to separate nitrogen (N) and oxygen (O). There are instruments with higher resolution that increase the length of the TOF to allow for the separation of N and O, but they face resource limitations. Therefore, this research aims to design a compact ion mass spectrometer that can be mounted on a CubeSat-class spacecraft, while still being able to separate N and O.
To separate N and O, this research focuses on negative ions of O. It is known that when incident ions pass through the carbon thin foil at the entrance of the mass spectrometer, most of the O+ ions undergo charge exchange, resulting in neutral particles or negative ions. On the other hand, the ratio of N that forms negative ions through charge exchange is much smaller compared to O. Therefore, if negative ions and neutral particles can be separated and measured, the ratio of N to O can be determined without needing to resolve them in TOF.
Based on this idea, specific device shapes were examined through numerical simulations. By creating a potential gradient in the radial direction, the O and O- detection positions were successfully separated in a TOF unit with a height of 30 mm. The potential was set to -4.9 kV at the entrance and -3.0 kV at the detection section, for example. Since both the electrostatic analyzer and the MCP (Microchannel Plate) also use negative polarity for the high voltage, one advantage of this design is that only a single type of high-voltage element is needed. Additionally, it was confirmed through calculations that carbon (C), which has a negative ion generation rate similar to O, can be distinguished from O ions using only TOF with sufficient resolution.
To separate N and O, this research focuses on negative ions of O. It is known that when incident ions pass through the carbon thin foil at the entrance of the mass spectrometer, most of the O+ ions undergo charge exchange, resulting in neutral particles or negative ions. On the other hand, the ratio of N that forms negative ions through charge exchange is much smaller compared to O. Therefore, if negative ions and neutral particles can be separated and measured, the ratio of N to O can be determined without needing to resolve them in TOF.
Based on this idea, specific device shapes were examined through numerical simulations. By creating a potential gradient in the radial direction, the O and O- detection positions were successfully separated in a TOF unit with a height of 30 mm. The potential was set to -4.9 kV at the entrance and -3.0 kV at the detection section, for example. Since both the electrostatic analyzer and the MCP (Microchannel Plate) also use negative polarity for the high voltage, one advantage of this design is that only a single type of high-voltage element is needed. Additionally, it was confirmed through calculations that carbon (C), which has a negative ion generation rate similar to O, can be distinguished from O ions using only TOF with sufficient resolution.