Investigations of Solid-State Detectors for Time-of-Flight Mass Spectrometry, 15-9199

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Principal Investigators
Martin P. Wüest
Ron Bowman
Scott E. Weidner

Inclusive Dates: 07/01/00 - 02/18/02

Background - SwRI has participated in recent years in the design and development of several mass spectrometers. Typical time-of-flight mass spectrometers for space flight most often include an electrostatic analyzer for energy per charge analysis and a time of flight section for velocity or mass determination. The ions are usually detected with microchannel plates. The addition of a solid-state detector to determine the residual energy of the ion allows the unambiguous determination of mass, charge, and energy independently, instead of obtaining just ratios of energy/charge or mass/charge. To resolve ions according to their charge state becomes important in determining the isotopic composition and charge state of the solar wind, or in quantifying minor ions in the Earth's magnetosphere. The Institute has little experience in solid-state detectors for space applications, and this internal research is directed to change this lack of experience.

Approach - To gain experience with solid-state detectors for space flight mass spectrometry, the research team tested a commercially available solid-state detector in the SwRI ion calibration facility. In addition team members developed a front-end, space-qualifiable electronics board to read out the weak signals. To get an energy threshold as low as possible, a very low noise electronics board is required. Finally, the team resolved some system design issues with operating a solid-state detector on a 30-kilovolt floating power supply.

Accomplishments - Performing tests in the SwRI ion accelerator facility and using commercially available electronics, the team determined an energy detection threshold for argon of 15 keV using a large passivated, implanted, planar silicon detector of 14 by 14 mm2 size and 300-micrometer depletion depth. Several studies were performed to reduce the noise further in a space flight application (for example, smaller detector size, thermal-electric cooling). The present energy detection threshold is 10 keV in a bench top setting. A custom-built pre-amplifier board was built. The team concluded that the system design described in the literature with analog front-end electronics floating on high voltage is still the best way to build a triple-coincidence mass spectrometer.

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