9:45 AM - 10:00 AM
[PCG20-04] Development of a Neutral Mass Spectrometer for the Ionosphere Observation by S-310-46 Sounding Rocket
Keywords:Neutral Mass Spectrometer, Composition of the Ionospheric Neutral Atmosphere, Sounding Rocket
The composition of the neutral atmosphere in the ionosphere affects the collision frequency between the neutral atmosphere and the plasma, which in turn affects the electrical conductivity of the ionospheric current. Therefore, it is necessary to observe the neutral atmospheric composition in order to reveal the structure of the ionospheric current and the electric field that interacts with the current. Installing a neutral mass spectrometer on board a flight vehicle is a common method of observation, but the large size of the neutral mass spectrometer has reduced the number of observation opportunities in recent years. Therefore, we have developed a compact neutral mass spectrometer suitable for the installation on a flying vehicle. This instrument will be installed on S-310-46 sounding rocket, which is scheduled to be launched in the summer of 2024, to observe the neutral atmospheric composition at an altitude of about 100 km to 130 km.
The mass analyzer part of the instrument is the same type as that of TRITON, which is a mass spectrometer developed for the LUnar Polar EXploration mission LUPEX, and employs a time-of-flight reflectron. In the instrument, by switching the voltage of each electrode in the ion source and the mass analyzer part, it is possible to switch between a single reflection mode with high sensitivity but low mass resolution and a triple reflection mode with low sensitivity but high mass resolution. The mass analyzer part of TRITON was about 188 mm, but it was downsized to about 112 mm for the installation on the S-310 rocket. Through performance tests, the mass resolution was confirmed to be over 100 in the single reflection mode and over 200 in the triple reflection mode. The ion source and detector are the same as those developed for TRITON. The ion source is a small electron impact ion source equipped with two iridium filaments coated with Y2O3 for redundancy (Kawashima et al. 2022). The detector is a two-stage micro-channel plate. The mass analyzer part, ion source and detector together fit into 156x187x130mm including the outer box.
In addition, a spherical antechamber with a diameter of 50mm is attached in front of the ion source as a particle intake. Neutral atmospheric particles entering the device at the relative velocity of a rocket speed collide with the inner wall of the antechamber repeatedly before being introduced into the ion source, and are thermalized to a temperature equivalent to the wall temperature of the antechamber. This reduces the ununiformity of the temperature and allows for more quantitative observations. Since highly reactive substances like atomic oxygen react during collisions with the wall and adversely affect the observation of other components, the inner wall is gold plated to suppress these reactions.
The mass analyzer part of the instrument is the same type as that of TRITON, which is a mass spectrometer developed for the LUnar Polar EXploration mission LUPEX, and employs a time-of-flight reflectron. In the instrument, by switching the voltage of each electrode in the ion source and the mass analyzer part, it is possible to switch between a single reflection mode with high sensitivity but low mass resolution and a triple reflection mode with low sensitivity but high mass resolution. The mass analyzer part of TRITON was about 188 mm, but it was downsized to about 112 mm for the installation on the S-310 rocket. Through performance tests, the mass resolution was confirmed to be over 100 in the single reflection mode and over 200 in the triple reflection mode. The ion source and detector are the same as those developed for TRITON. The ion source is a small electron impact ion source equipped with two iridium filaments coated with Y2O3 for redundancy (Kawashima et al. 2022). The detector is a two-stage micro-channel plate. The mass analyzer part, ion source and detector together fit into 156x187x130mm including the outer box.
In addition, a spherical antechamber with a diameter of 50mm is attached in front of the ion source as a particle intake. Neutral atmospheric particles entering the device at the relative velocity of a rocket speed collide with the inner wall of the antechamber repeatedly before being introduced into the ion source, and are thermalized to a temperature equivalent to the wall temperature of the antechamber. This reduces the ununiformity of the temperature and allows for more quantitative observations. Since highly reactive substances like atomic oxygen react during collisions with the wall and adversely affect the observation of other components, the inner wall is gold plated to suppress these reactions.