Development of an electron impact ion source with high ionization efficiency for future planetary missions

TL;DR

This paper presents a new high-emission electron impact ion source with a Y2O3-coated iridium filament, achieving tenfold increased electron emission and ionization efficiency, suitable for future planetary mass spectrometry missions.

Contribution

The study introduces a novel EI ion source with a Y2O3-coated iridium filament that significantly enhances electron emission and ionization efficiency compared to previous models.

Findings

Electron emission exceeds 2 mA at 3.0 W power

Ionization efficiency reaches 10^4 nA/Pa

Demonstrated durability over 30 min * 100 cycles

Abstract

Ion sources using electron impact ionization (EI) methods have been widely accepted in mass spectrometry for planetary exploration missions because of their simplicity. Previous space-borne mass spectrometers were primarily designed with the EI method using rhenium tungsten alloy filaments, enabling up to 200 uA emission in typical cases. The emission level is desired to be enhanced because the sensitivity of mass spectrometers is a critical requirement for the future in situ mass spectrometry related to the measurement of trace components in planetary samples. In this study, we developed a new high-emission EI ion source using a Y2O3-coated iridium filament, which has a lower work function than rhenium tungsten alloy. The size of the ion source was 30 mm * 26 mm * 70 mm, and its weight was 70 g. We confirmed that when consuming 3.0 W power, the ion source emits more than 2 mA electrons, which is 10 times greater than the previous models electron emission level. Ionization efficiency of the EI ion source is proportional to the amount of electron emission, which implies our new model increased the ionization efficiency 10 times. We conducted performance tests on the prototype with the 3.0 W heating condition, confirming a high ionization efficiency (10^4 nA/Pa). In addition, we conducted endurance tests of the ion source and demonstrated the persistence of the ionization efficiency for 30 min * 100 cycles.