[en] Full text: Until the development of the Plasma Ion Mass Spectrometer (PIMS) there was no device available for measuring the absolute flux of ions in each charge state flowing in the edge plasma of tokamaks (magnetic fusion devices). Besides the knowledge of the local density in the edge region the PIMS can give an indication of the average ion temperature of the impurities [1]. The charge state distribution and absolute flux of impurities is dependent on the location and magnitude of the impurity sources and the transport of impurity ions within the scrape-off layer (SOL) and on closed flux surfaces. The benefit of mass spectrometry compared to passive spectroscopic methods is that a full evaluation of species in the plasma edge can be achieved by this in-situ measurement at a very precisely defined point in space [1] with no dependence on the accuracy of photon efficiencies. The PIMS is a trochoidal mass spectrometer that uses the magnetic field for the confinement of the plasma as its B-field. Thus only electrostatic voltages are needed for the operation of this instrument. Ion optics simulations done by SIMION 6 [2] as well as the similar custom written code in JET [1] compute the transmission for the range of ion mass and charge we expect to see in the edge of JET. Our simulations confirm that the geometry of the PIMS chosen has transmission characteristics that are not too sensitive to sheath voltage and ion temperature, and that magnetic field misalignment does not significantly degrade the resolution. (author)