10:45 AM - 11:00 AM
[PCG18-01] Development of a space-borne electron impact ion source optimizing ionization rate
Keywords:Space exploration, Electron gun, Ion source
Mass spectrometer is one of the powerful tools to analyze elemental/isotopic compositions of planetary neutral atmosphere. In many previous missions, the instrument has been great help to understand the history and evolution of planets. In MAVEN mission, for example, mass spectrometer named NGIMS has successfully observed Martian neutral atmospheric escape rate to reconstruct Martian ancient atmosphere. For mass spectrometers in future missions, higher sensitivity is desired to measure trace components, such as noble gases and isotopic diversity. For the purpose, we are developing ionization source with increased ionization rates in this study.
In most of the previous planetary missions, ion sources are designed with electron impact ionization method for the simplicity of the technique.Although 3% Re-W alloy filaments are conventionally used and have a lot of flight-proven performance (e.g., Mahaffy et al., 2012), we selected Iridium filaments with Y2O3 coating for the low work function. Based on the Richardson equation, lower work-function materials enable more electrons to be emitted at the same temperature. Consequently, we confirmed 10-times higher electron emissions in safety with our new model (>2 mA) than that of the previous model (~200 μA, Mahaffy et al., 2012) in our laboratory experiments. Additionally, we established linear relationship between sample gas abundance and extracted ion current (~1×104 nA/Pa) within 1% accuracy for both tandem optics, which we mounted for the redundancy. Then we conducted endurance performance test (ON/OFF = 30min/1hour × 100cycle, 8hour/1hour × 100cycle), verifying the feasibility and robustness of the ion source with the repetitive operation by rapid switching.
In most of the previous planetary missions, ion sources are designed with electron impact ionization method for the simplicity of the technique.Although 3% Re-W alloy filaments are conventionally used and have a lot of flight-proven performance (e.g., Mahaffy et al., 2012), we selected Iridium filaments with Y2O3 coating for the low work function. Based on the Richardson equation, lower work-function materials enable more electrons to be emitted at the same temperature. Consequently, we confirmed 10-times higher electron emissions in safety with our new model (>2 mA) than that of the previous model (~200 μA, Mahaffy et al., 2012) in our laboratory experiments. Additionally, we established linear relationship between sample gas abundance and extracted ion current (~1×104 nA/Pa) within 1% accuracy for both tandem optics, which we mounted for the redundancy. Then we conducted endurance performance test (ON/OFF = 30min/1hour × 100cycle, 8hour/1hour × 100cycle), verifying the feasibility and robustness of the ion source with the repetitive operation by rapid switching.