Design and Fabrication of a high resolution Radio-Frequency Quadrupole Mass Analyser

A radio frequency Quadrupole Mass Analyser (QMA) separates ions of different charge-tomass ratio by exploiting the phenomenon of parametric resonance for charged particles moving through an AC quadrupole field. We have studied the standard configurations of QMAs in detail with extensive simulations, and have accurately calculated the non-linear corrections to the quadrupole field. We have also found a novel configuration of electrodes which has much better field linearity due to simultaneous cancellation of several higher moments, and this should enable us to push the current limit on resolution set by non-linear resonances. We have almost completed the fabrication of a conventional QMA from scratch, including a quadrupole of 4 cylindrical electrodes, an Electron Impact (EI) ion source for producing a collimated beam of ions from a gas sample, a Faraday Cup detector arrangement with associated low-noise electronics, and the vacuum chambers to house the entire arrangement. We will proceed with the fabrication of the improved quadrupole arrangement after successfully testing the conventional QMA.