Particle Dynamics Calculations and Emittance Measurements at the Fets *

High power proton accelerators in the MW range have many applications including drivers for spallation neutron sources, neutrino factories, transmuters (for transmuting long-lived nuclear waste products) and energy amplifiers. In order to contribute to the development of HPPAs, to prepare the way for an ISIS upgrade and to contribute to the UK design effort on neutrino factories, a front end test stand (FETS) is being constructed at the Rutherford Appleton Laboratory (RAL) in the UK. The aim of the FETS is to demonstrate the production of a 60 mA, 2 ms, 50 pps chopped beam at 3 MeV with sufficient beam quality. An overview on the status of the project together with the results of numerical simulations of the particle dynamics from the ion source to the RFQ exit will be presented. The particle distributions gained from the particle dynamics simulations will be compared with recent measurements of the transversal beam emittance behind the ion source and the results discussed.