J. A. MacAskill

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.

Dipole Excitation With A Paul Ion Trap Mass Spectrometer

Preliminary results are presented for the use of an auxiliary radiofrequency (rf) excitation voltage in combination with a high purity, high voltage rf generator to perform dipole excitation within a high precision Paul ion trap. These results show the effects of the excitation frequency over a continuous frequency range on the resultant mass spectra from the Paul trap with particular emphasis on ion ejection times, ion signal intensity, and peak shapes. Ion ejection times are found to decrease continuously with variations in dipole frequency about several resonant values and show remarkable symmetries. Signal intensities vary in a complex fashion with numerous resonant features and are driven to zero at specific frequency values. Observed intensity variations depict dipole excitations that target ions of all masses as well as individual masses. Substantial increases in mass resolution are obtained with resolving powers for nitrogen increasing from 114 to 325.

Measurements of polyatomic molecule formation on an icy grain analog using fast atoms

Measurements are reported for production of CO{sub 2} resulting from the impact of a monoenergetic O({sup 3}P) beam upon a surface cooled to 4.8 K and covered with a CO ice. Using temperature-programmed desorption and mass spectrometer detection, one clearly detects increasing amounts of CO{sub 2} formation with O({sup 3}P) energies of 2, 5, 10, and 14 eV. This is a measurement of polyatomic molecule formation on a surface in a new regime using superthermal atoms. The chosen surface coverage, surface temperature, and superthermal atom energy simulate conditions in shock-heated circumstellar and interstellar regions.

Collision physics in the atomic and molecular universe

The wavelength range and high resolution of the space instruments Chandra, Newton, SOHO, Suzaku, Herschel, Spitzer, and the upcoming ASTRO-H and James Webb Space Telescope have increased the need for laboratory collision-physics measurements to interpret astrophysical phenomena. A review will be given of charge exchange of highly-charged ions with neutral comet and planet atmospheres; and the formation of complex molecules in stellar regions. These space observations are linked to laboratory measurements of absolute charge-exchange cross sections; and molecular formation of species such as CO2, CH3OH, and CH3CH2OH involving fast H- and O-atom collisions with abundant interstellar molecules adsorbed on dust-grain analogues.

Absolute cross sections for single and multiple charge exchange in Feq+ impacting on CO, CO2 and H2O

We report measured absolute single and multiple charge-exchange cross sections for Feq+ ions colliding with CO, CO2 and H2O. A retarding-field method is used in two different approaches for charge-state analysis of the ion beam after traversing the stationary target gas cell. The projectile energy is 7q keV. This corresponds to a range of ion velocities of 350 km s−1 for q = 5, to 560 km s−1 for q = 13. This is comparable to solar wind velocities for understanding charge exchange of solar wind ions with cometary neutrals, leading to X-ray emission from the ions.