Murray Darrach

Digitally synthesized high purity, high-voltage radio frequency drive electronics for mass spectrometry.

Reported herein is development of a quadrupole mass spectrometer controller (MSC) with integrated radio frequency (rf) power supply and mass spectrometer drive electronics. Advances have been made in terms of the physical size and power consumption of the MSC, while simultaneously making improvements in frequency stability, total harmonic distortion, and spectral purity. The rf power supply portion of the MSC is based on a series-resonant LC tank, where the capacitive load is the mass spectrometer itself, and the inductor is a solenoid or toroid, with various core materials. The MSC drive electronics is based on a field programmable gate array (FPGA), with serial peripheral interface for analog-to-digital and digital-to-analog converter support, and RS232/RS422 communications interfaces. The MSC offers spectral quality comparable to, or exceeding, that of conventional rf power supplies used in commercially available mass spectrometers; and as well an inherent flexibility, via the FPGA implementation, for a variety of tasks that includes proportional-integral derivative closed-loop feedback and control of rf, rf amplitude, and mass spectrometer sensitivity. Also provided are dc offsets and resonant dipole excitation for mass selective accumulation in applications involving quadrupole ion traps; rf phase locking and phase shifting for external loading of a quadrupole ion trap; and multichannel scaling of acquired mass spectra. The functionality of the MSC is task specific, and is easily modified by simply loading FPGA registers or reprogramming FPGA firmware.

Recent Developments in Gas Chromatographs and Mass Spectrometers for Crewed and Robotic Space Missions

We report progress towards developing the micro-Gas Monitor (mGM), a miniature gas chromatograph mass spectrometer. The mGM is planned to have a total mass of 2.5kg and consume approximately 22W of power, including pumps and all electronics. The instrument consists of JPL’s quadrupole ion trap mass spectrometer integrated with a state-of-the-art micro-electromechanical gas chromatograph system developed by Cbana Labs Inc. The base characteristics of the mGM are: mass range from 1amu to 2000amu; mass resolving power of 800 @ mass 40 and sensitivity at parts-per-billion level. The low instrument mass, coupled with its high analytical capabilities, makes the mGM ideally suitable for wide range of applications such as trace contaminant and major constituent monitoring in crewed space exploration vehicles or robotic planetary missions. Presented are mGM data for both trace volatile organic and real-time major constituents detection.

The Mass Analyzer for Real-time Investigation of Neutrals at Europa (MARINE)

Presented herein is the progress on developing a new mass analyzer for analysis of the exospheres of planets, moons, and primitive bodies, such as found at Europa or Enceladus. Europa, one of Jupiters four Galilean moons, may have a subsurface ocean plausibly containing the key ingredients for life as well as sources of chemical energy. Clues to the composition and chemical state of Europas ocean can be found both on Europas icy surface and in its tenuous atmosphere. Given the high scientific priority of assessing the habitability of Europas ocean, the Europa Clipper notional payload includes a Neutral Mass Spectrometer whose purpose is to characterize the composition of ejected surface products during a series of flyby investigations. The Mass Analyzer for Real-time Investigation of Neutrals at Europa (MARINE) is capable of measuring the abundances of neutral particle species in Europas exosphere including H2O, O2, CO2, and SO2, and determining their number density profiles at per-second sampling rates as a function of altitude above Europas surface. MARINE will either detect tracers of potential subsurface biological activity in Europas exosphere, or place upper limits on their surface abundances. It exceeds all requirements for the proposed investigations with margins ranging from 100 to 1000%, while remaining fully compatible with spacecraft accommodation constraints for mass, power, data volume, and field-of-view.

Computer Modeling of an Ion Trap Mass Analyzer, Part I: Low Pressure Regime

AbstractWe present the multi-particle simulation program suite Computational Ion Trap Analyzer (CITA) designed to calculate the ion trajectories within a Paul quadrupole ion trap developed by the Jet Propulsion Laboratory (JPL). CITA uses an analytical expression of the electrodynamic field, employing up to six terms in multipole expansion and a modified velocity-Verlet method to numerically calculate ion trajectories. The computer code is multithreaded and designed to run on shared-memory architectures. CITA yields near real-time simulations with full propagation of 26 particles per second per core. As a consequence, a realistic numbers of trapped ions (100+ million) can be used and their trajectories modeled, yielding a representative prediction of mass spectrometer analysis of trace gas species. When the model is compared with experimental results conducted at low pressures using the conventional quadrupole and dipole excitation modes, there is an excellent agreement with the observed peak shapes. Owing to the program’s efficiency, CITA has been used to explore regions of trapping stability that are of interest to experimental research. These results are expected to facilitate a fast and reliable modeling of ion dynamics in miniature quadrupole ion trap and improve the interpretation of observed mass spectra. Graphical Abstractᅟ

High-precision measurements of krypton and xenon isotopes with a new static-mode Quadrupole Ion Trap Mass Spectrometer

Measuring the abundance and isotopic composition of noble gases in planetary atmospheres can answer fundamental questions in cosmochemistry and comparative planetology. However, noble gases are rare elements, a feature making their measurement challenging even on Earth. Furthermore, in space applications, power consumption, volume and mass constraints on spacecraft instrument accommodations require the development of compact innovative instruments able to meet the engineering requirements of the mission while still meeting the science requirements. Here we demonstrate the ability of the quadrupole ion trap mass spectrometer (QITMS) developed at the Jet Propulsion Laboratory (Caltech, Pasadena) to measure low quantities of heavy noble gases (Kr, Xe) in static operating mode and in the absence of a buffer gas such as helium. The sensitivity reaches 10^(13) cps Torr^(−1) (about 10^(11) cps Pa^(−1)) of gas (Kr or Xe). The instrument is able to measure gas in static mode for extended periods of time (up to 48 h) enabling the acquisition of thousands of isotope ratios per measurement. Errors on isotope ratios follow predictions of the counting statistics and the instrument provides reproducible results over several days of measurements. For example, 1.7 × 10^(−10) Torr (2.3 × 10^(−8) Pa) of Kr measured continuously for 7 hours yielded a 0.6‰ precision on the ^(86)Kr/^(84)Kr ratio. Measurements of terrestrial and extraterrestrial samples reproduce values from the literature. A compact instrument based upon the QITMS design would have a sensitivity high enough to reach the precision on isotope ratios (e.g. better than 1% for ^(129,131–136)Xe/^(130)Xe ratios) necessary for a scientific payload measuring noble gases collected in the Venus atmosphere.

Dissociative Electron Attachment to NO, CO and N2O in a 0.5 T Magnetic Field

Dissociative electron attachment to CO, NO and N2O is studied in a 0.5 T magnetic field. The magnetic field dependence of the attachment process is analyzed to understand the possible role of magnetically-coupled excited molecular states. The present technique converts the O−(2P) ions produced by the attachment to fast O(3P) by steps of ion acceleration and laser photodetachment. The resulting fast O(2P) atoms are then detected with a microchannel plate. This method facilitates analysis of any B-field enhancements in the resonant attachment phenomena, with minimal contribution from backgrounds of positive and negative charges.