10:45 AM - 12:15 PM
[PCG18-P04] Development of Neutral Mass Spectrometer for the Observations of the Ionosphere
Keywords:Mass spectrometer, Neutral atmospheric composition, Sporadic E layer
Plasma motion in the ionosphere is governed not only by the electromagnetic force but also by the collisions with atmospheric neutral particles. Since the frequencies of collisions depend on the species of colliding particles, the measurement of the atmospheric composition is necessary for the comprehensive observation of plasma phenomena in the ionosphere. However, the atmospheric composition has rarely been measured in recent in-situ observations of the ionosphere partly because mass spectrometers tend to be large. Therefore, we are developing a small neutral mass spectrometer that can be mounted on sounding rockets and low earth orbit satellites and measures the atmospheric composition and density. The developed instrument will be used in S-310-46 sounding rocket experiment targeting sporadic E layers in the summer of 2024 and give the altitude profiles of the atmospheric composition and density of major neutral species such as O, O2, and N2 from 90 km to 130 km altitude.
The neutral mass spectrometer is based on a time-of-flight mass spectrometer named TRITON, which has been developed by ISAS/JAXA for the investigation of water in the soil of lunar polar regions. In the principle of a time-of-flight mass spectrometer, the longer particles fly in the instrument, the better its mass resolution gets. However, the size of the instrument becomes bigger at the same time. To achieve sufficient mass resolution with a small size, particles are reflected three times in TRITON.
Since the mass analyzing part needs to be downsized for S-310 rocket, we newly designed the length and voltage of each part based on the ion optical conditions. The mass resolution and sensitivity with the new design were evaluated by particle simulations. According to the results, the mass resolution is within the expected range, while the sensitivity shows different trends from the TRITON evaluation because flying particles collide with electrodes and walls unexpectedly. However, these performances are sufficient for S-310-46 observation. The analyzing part has been manufactured. We are going to evaluate its performance and acquire its characteristics by tests in 2023.
In addition, we are newly developing an entrance part called an antechamber which is particularly necessary for the measurements onboard sounding rockets and satellites. Particles enter the instrument with the relative velocity of their thermal speed plus the vehicles’ speed. If the particles enter the analyzing part directly, it is difficult to measure the mass and density properly. To avoid this, a spherical antechamber is attached before the intake. Particles entering the antechamber get decelerated down to their thermal speed through collisions with the inner wall. Moreover, the density in the antechamber is enhanced compared to the ambient density which could contribute to the increase of the measurement sensitivity. We are designing the antechamber by examining how its size and its holes’ positions and diameters influence these two major roles.
The neutral mass spectrometer is based on a time-of-flight mass spectrometer named TRITON, which has been developed by ISAS/JAXA for the investigation of water in the soil of lunar polar regions. In the principle of a time-of-flight mass spectrometer, the longer particles fly in the instrument, the better its mass resolution gets. However, the size of the instrument becomes bigger at the same time. To achieve sufficient mass resolution with a small size, particles are reflected three times in TRITON.
Since the mass analyzing part needs to be downsized for S-310 rocket, we newly designed the length and voltage of each part based on the ion optical conditions. The mass resolution and sensitivity with the new design were evaluated by particle simulations. According to the results, the mass resolution is within the expected range, while the sensitivity shows different trends from the TRITON evaluation because flying particles collide with electrodes and walls unexpectedly. However, these performances are sufficient for S-310-46 observation. The analyzing part has been manufactured. We are going to evaluate its performance and acquire its characteristics by tests in 2023.
In addition, we are newly developing an entrance part called an antechamber which is particularly necessary for the measurements onboard sounding rockets and satellites. Particles enter the instrument with the relative velocity of their thermal speed plus the vehicles’ speed. If the particles enter the analyzing part directly, it is difficult to measure the mass and density properly. To avoid this, a spherical antechamber is attached before the intake. Particles entering the antechamber get decelerated down to their thermal speed through collisions with the inner wall. Moreover, the density in the antechamber is enhanced compared to the ambient density which could contribute to the increase of the measurement sensitivity. We are designing the antechamber by examining how its size and its holes’ positions and diameters influence these two major roles.