A novel principle for an ion mirror design in time-of-flight mass spectrometry

A novel design for a gridless two-stage ion mirror, or reflectron, for time-of-flight mass spectrometry (TOFMS) will be presented. The development of this novel design was driven by the stringent engineering requirements for the ion mirror's utilization by the reflectron time-of-flight (RTOF) sensor in the Rosetta orbiter spectrometer for ion and neutral analysis (ROSINA) instrument package of the Rosetta cometary mission launched by the European Space Agency in March 2004.The reflectron consists of ceramic and titanium alloy components joined by brazing and welding processes. The device serves as both the mechanical structure and as an ultra-high-vacuum (UHV) enclosure for the TOFMS system. The electrostatic fields of the reflectron are generated along two individually adjustable sections of a resistor helix applied to the inner surface of a ceramic cylinder. This design allows for increased homogeneity of the electrostatic fields, and minimizes fringe fields close to the cylindrical boundary of the reflectron structure. Thus, the usable inner diameter of ion flight path for a given outer diameter is maximized; a feature required by spacecraft constraints. An additional electrostatic lens in front of the reflectron allows the geometrical alteration of the shape of the ion beam, and its direction with regard to the ion optical axis. This makes it possible to switch the operation of the TOFMS system between a single-reflection and a triple-reflection mode, the latter using an additional ion mirror. Typically, mass resolutions of up to 5000 at full width at half maximum (FWHM) have been achieved in the triple-reflection mode for an overall sensor dimension of 1 m. Experimental results in the single-reflection mode and in the triple-reflection mode will be presented. Environmental constraints for space applications will also be discussed.