10:00 AM - 10:15 AM
[PCG17-07] Development of a Time of Flight Mass Spectrometer (TRITON) for Lunar Polar Exploration (LUPEX)
Keywords:LUPEX, mass spectrometer
Investigation of the amount and the chemical form of volatiles including water on the lunar surface is important not only in understanding the evolution of the lunar surface, but also in understanding the origin of lunar and terrestrial water and the transportation of materials in the solar system. In addition, if the quantity of volatiles on the Moon is substantial, space exploration based on the Moon may be possible converting them into fuels. Therefore, exploration of the lunar poles is important in both planetary science and advancement of space exploration.
Although remote observations suggest the presence of water on the lunar surface, it is still unclear that how much water exists. LCROSS (Lunar Crater Observation and Sensing Satellite) operated by NASA is one of the examples of the remote observations. A part of a rocket impacted a permanent shadowed region in a crater Cabeus in the lunar south pole, and the generated dust plume was observed [1]. Water and small amount of hydroxyl, the amount of which is 0.03 % of water, were observed. It is unknown whether the hydroxyl was derived from photodissociation of water or desorption from grains in the regolith. A small abundance of other volatiles was also detected. Since the mass spectrometer should be able to distinguish large amount of water and small abundance of other volatiles, high mass resolution is required in order to achieve scientific goals such as determination of the origin of hydroxyl and the abundance of volatiles on the lunar surface.
JAXA is planning LUPEX (LUnar Polar Exploration) mission collaborating with Indian Space Research Organization. REIWA (REsource Investigation Water Analyzer) is one of the instruments for investigating volatiles including water. REIWA consists of a heater with a weight scaler, which measures weight of the heated samples, and mass analyzers which analyze desorbed volatiles from the samples. We are developing triple-reflection reflectron (TRITON), which is a time-of-flight mass spectrometer (TOFMS). TRITON is composed of an ion source that generates ion beam with large area and a triple-reflection reflectron which is compact and has high mass resolution. TRITON is operated mainly with two different modes, single reflection mode in which particles are reflected once and triple reflection mode in which particles are reflected three times. The two operation modes can be switched by adjusting voltage applied to the analyzer. The single reflection mode is characterized by high sensitivity and low mass resolution. Although the triple reflection mode has lower sensitivity, the mass resolution is much higher than that of the single reflection mode.
The prototype of TRITON was optimized so that the triple reflection mode had the highest mass resolution. We have found by calculation that the single reflection mode can also be optimized by extending the length of the reflector. We will measure the change of the mass spectrum and will evaluate the mass resolution and sensitivity before and after extending the length of the reflector. We have also found that sometimes the mass spectrum of an ion splits to two peaks. The relative height of the two peaks varies depending on the size of the ion beam, which is determined by the size of the slit between the ion source and the entrance part of the mass spectrometer. We will present possible cause and a counter measure to solve the problem.
[1] A. Colaprete, et al, Science, 330, 6003, (2010)
Although remote observations suggest the presence of water on the lunar surface, it is still unclear that how much water exists. LCROSS (Lunar Crater Observation and Sensing Satellite) operated by NASA is one of the examples of the remote observations. A part of a rocket impacted a permanent shadowed region in a crater Cabeus in the lunar south pole, and the generated dust plume was observed [1]. Water and small amount of hydroxyl, the amount of which is 0.03 % of water, were observed. It is unknown whether the hydroxyl was derived from photodissociation of water or desorption from grains in the regolith. A small abundance of other volatiles was also detected. Since the mass spectrometer should be able to distinguish large amount of water and small abundance of other volatiles, high mass resolution is required in order to achieve scientific goals such as determination of the origin of hydroxyl and the abundance of volatiles on the lunar surface.
JAXA is planning LUPEX (LUnar Polar Exploration) mission collaborating with Indian Space Research Organization. REIWA (REsource Investigation Water Analyzer) is one of the instruments for investigating volatiles including water. REIWA consists of a heater with a weight scaler, which measures weight of the heated samples, and mass analyzers which analyze desorbed volatiles from the samples. We are developing triple-reflection reflectron (TRITON), which is a time-of-flight mass spectrometer (TOFMS). TRITON is composed of an ion source that generates ion beam with large area and a triple-reflection reflectron which is compact and has high mass resolution. TRITON is operated mainly with two different modes, single reflection mode in which particles are reflected once and triple reflection mode in which particles are reflected three times. The two operation modes can be switched by adjusting voltage applied to the analyzer. The single reflection mode is characterized by high sensitivity and low mass resolution. Although the triple reflection mode has lower sensitivity, the mass resolution is much higher than that of the single reflection mode.
The prototype of TRITON was optimized so that the triple reflection mode had the highest mass resolution. We have found by calculation that the single reflection mode can also be optimized by extending the length of the reflector. We will measure the change of the mass spectrum and will evaluate the mass resolution and sensitivity before and after extending the length of the reflector. We have also found that sometimes the mass spectrum of an ion splits to two peaks. The relative height of the two peaks varies depending on the size of the ion beam, which is determined by the size of the slit between the ion source and the entrance part of the mass spectrometer. We will present possible cause and a counter measure to solve the problem.
[1] A. Colaprete, et al, Science, 330, 6003, (2010)