In the ion source of the accelerator the protons are generated out of hydrogen gas. With the accelerator this protons are then accelerated to the maximum energy of 230 Mega electron Volts (MeV) needed to treat deep seated tumours in the human body.
The type of accelerator used is a cyclotron with fixed energy and continuous beam. Continuous beam is important for fast scanning needed for moving targets.
Right after the accelerator in the first part of the beamline the Energy Selection System (ESS) is installed. Here will the energy be chosen to define the position of the bragg peak in the tumour.