An approximate method for determining the emittance of ion sources in quadrupole mass spectrometry

Abstract An approximate method of determining the emittance of an ion source coupled to a quadrupole mass spectrometer is described. The method combines the conclusions of recent phase space dynamics calculations of quadrupole acceptance and experimentally-measured transmission curves with the d.c. voltage set to zero. The calculation of source emittance is carried out in one dimension and assumes cylindrical symmetry. An exact solution for the emittance, while possible in principle, would be very time consuming and so an iterative approximation was used. The accuracy of the result can be tested by using the calculated emittance to regenerate ion transmission curves. The method described provides a basis for further study of the effective coupling of ion sources to quadrupoles and some improvements to its accuracy are suggested for future work.