Abstract :
[en] This thesis presents the development of a new compact, high-performance, and
flexible-operation multiple-reflection time-of-flight mass spectrometer. The primary
application areas are nano-analytics and space exploration. The main components
of the developed mass spectrometer are a pulsed electron impact ion source and a
multiple-reflection mass analyzer. The design and optimization of these components
were supported by computer-aided methods developed as part of this work.
A novel optimization framework for versatile use in optimization applications within
the design of charged particle optics components has been developed. It combines
a multi-objective optimization algorithm based on genetic algorithms with workflows
for design modeling in the simulation environment SIMION. The automated
interaction between these modules is facilitated by a dedicated communication interface. These modules enable the simultaneous and independent Pareto optimization of many parameters of different types for two individual objective functions. The optimization and modeling are complemented by methods for post-optimization data analysis, which allow for a gradual reduction of the possible Pareto solution space to ultimately identify the most suitable solution. This includes a sensitivity analysis, which provides insight into the effects of parameter changes on the system output. High-performance designs with robustness against parameter deviations were achieved. To achieve a compact instrument design with high mass resolving power, a configuration was chosen for the mass analyzer consisting of two identical, rotationally symmetrical ion mirrors, each with seven electrodes, aligned axially against each other. This arrangement allows mutual reflection of the ions, creating a closed path for ion trajectories within the multiple-reflection cell. During operation, the performance in terms of mass resolving power can be flexibly adjusted by controlling the number of full-turns performed. The design of the ion mirrors was initially derived analytically but did not meet the required mass resolving power. Using the developed optimization framework, the mass analyzer’s design was significantly improved with respect to the applied potential distributions. Additionally, a new approach for the spatial focusing of the ion beam improved transmission characteristics. The operating modes of the mass analyzer are: (i) injection, in which particles are introduced into the multiple-reflection cell from the source; (ii) multiple-reflection operation, where particles oscillate back and forth between the ion mirrors and are separated by mass; and (iii) ejection, where particles are ejected from the multiple-reflection cell toward the detector. The pulsed ion source of the mass spectrometer allows ions to be introduced into the mass analyzer at a defined start time. To achieve this, the design of a continuously emitting electron impact ion source was modified to divide operation into a trapping phase and a pulsed extraction phase. The accumulation of particles during the trapping phase allows measurements with significantly enhanced sensitivity. A new extraction method has been developed that significantly reduces background noise in the spectrum by synchronizing the electron beam for ionization with the ion extraction. This results in measurements with a higher signal-to-noise ratio. Simulations of the complete mass spectrometer system yielded a mass resolving power of M/ΔM (full-width at half maximum) greater than 20,000 for m/z at 40 amu/e, with 400 full-turns and a total flight time of 1.5 ms at the detector plane. The clear separation of two closely spaced isotope peaks, 18O at 17.9992 amu/e and H2O at 18.0106 amu/e, was demonstrated in operation with at least 100 full-turns, highlighting the instrument’s suitability for high-precision analyses. The simulation design has been transferred to a prototype, which will undergo experimental testing in a follow-up project. The prototype has a total length of less than 50 cm and weighs 2.5 kg. However, this prototype, intended for proof-of-concept testing, is based on a modified, existing bulky ion source. The eventual use of a miniaturized, custom designed ion source is intended to achieve a more compact design. The mass analyzer prototype has a total length of 20 cm, an axial drift length of 7.5 cm, a maximum diameter of 5.5 cm, and weighs less than 1 kg. The developed mass spectrometer meets the requirements for compactness and performance necessary for applications in nano-analytics and space exploration.
