Two screen dipole spectrometer for laser wake field accelerators

Today's Laser-plasma-accelerators have high shot to shot energy spread, divergence and pointing fluctuations, but the mean beam energy is one of the most important parameters of any accelerator experiment. It has major impact on many accelerator applications and has to be well known in order to understand further results. An initial deflection angle of the beam from the design axes can yield a big error in energy measurement using a usual (one screen) dipole spectrometer. Two-screen-Dipole-Spectrometers (TSDS) enable to measure the mean beam energy and initial deflection angle separately by using a second screen in order to measure the beam position and direction of momentum behind the dipole. The talk aims to demonstrate methods to describe particle trajectories through TSDS' of relativistic particles that enter the dipole with initial deflection angles. In particular, optimal screen arrangements, that result a maximum resolution in energy and deflection angle measurement, are presented. Furthermore, TSDS' enable separate energy spread and divergence measurement for sufficient resolution in energy and deflection angle measurement.