Theoretical comparison of closed and open ICR cells

An analytical model is employed to compare the trapping potentials of open and closed cylindrical ICR traps. The potential is expanded into a Fourier Bessel series, which is evaluated with the help of a computer program. The parameters, directly accessible from that representation are the potential well depth and ion capacity. It transpires that the open cell has lower well depth and ion capacity over a range of dimensions, but can be shaped to nearly the same values as the closed cell. The discussion of the quality of the trapping potential is performed with the help of a polynomial representation, where the theoretical frequency shift is derived and compared with an experimentally observed frequency shift, where agreement is found. The deviation of the trapping potential of the quadrupolar shape is discussed with the polynomial representation and with the Fourier Bessel series representation. Open and closed cells show different behavior in that respect. The excitation behavior is examined, again with a polynomial representation of the trapping and excitation field, and with the help of numerical trajectory calculations. The relative size of the excitation detection ring determines the ratio of radial to axial excitation. (C) 1997 Elsevier Science B.V.