This report is a summary of the detailed calculations for designin the ESS main loss detector. It starts with describing the ESS project and the proton accelerator. Then, the general requirements for the loss detectors are listed. Based on these requirements few detectors are chosen. The main loss detector is chosen to be a cylindrical ionization chamber and a new design is given based on the time response calculations.
The new prototype detector response functions are calculated using the MARS and Geant4 particle transport codes. The response functions are simulated for different particle types, energies and incident angle.