First Ideas on Measuring Beam Energy and Energy Spread of the 160 MeV Linac4 H- beam with Detached Electrons

The experimental method presented in this note is to measure beam energy and energy spread of the 160 MeV Linac4 H beam. It could be must be considered as a potential alternative to measurements within the LBS line [1]. The concept is based on measuring the energy distribution of electrons being detached from H ions by interactions with the rest gas atoms inside the beam pipe. The physical point of view exploits that H ions and electrons travel at the same velocity, so that even after detachment the electron energy is correlated to the beam energy. Kinematic calculations reveal that Linac4 beam energy and electron energy scale according to the ratio of the H mass M and the electron mass m, i.e. M/m ≈ 1838. Hence, the expected mean electron energy is about 86.6 keV (with ELinac4 = 159.2 MeV), while the energy spread is about 46.2 eV (with σE,Linac4 ≈ 85 keV).