LINEARITY AND QUADRUPOLARITY OF TETRAGONAL AND CYLINDRICAL PENNING TRAPS OF ARBITRARY LENGTH-TO-WIDTH RATIO

The two most popular Penning traps in use for Fourier transform ion cy clotron resonance (FT-ICR) mass spectrometry are tetragonal (i.e., ort horhombic with square cross section) and cylindrical. Here we compare tetragonal and cylindrical traps as a function of aspect (length-to-wi dth) ratio and position within the trap, by comparing the numerically computed (from Simion 6.0) electric potential field of a given trap re lative to each of three idealized potentials required for ET-ICR exper iments: dipolar one-dimensional potential for alternating current (ac) excitation/detection of cyclotron motion, azimuthal two-dimensional q uadrupolar potential for ac excitation for ion axialization, and axial three-dimensional quadrupolar potential for direct current axial conf inement of ions. Our numerically computed results agree well with thos e previously derived analytically. The numerical approach provides a s impler and more accessible means for analyzing the aforementioned pote ntials. Moreover, the numerical approach (unlike the analytical approa ch) readily extends to traps of lower even when analytical solutions a re available, the numerical method presented here is complementary, si nce it provides a useful check on the validity of the derived equation s. (C) 1997 American Society for Mass Spectrometry.