RF deflector based measurements of the correlations between vertical and longitudinal planes at ELI-NP-GbS electron linac

The correlations between vertical and longitudinal planes at the Radio Frequency Deflector (RFD) entrance can be introduced by misalignments of accelerating sections or quadrupoles upstream of the RFD. These correlations are undesired effects and they can affect the RFD based bunch length measurements in high-brightness electron LINAC. In this paper, an RFD based measurement technique for vertical and longitudinal planes is proposed. The basic idea is to obtain information about the correlations between vertical and longitudinal planes from vertical spot size measurements varying the RFD phase, because they add contributions on this quantity. In particular, considering a small RFD phase range centred in 0 or π rad, the correlations between the particle longitudinal positions and the vertical plane are constant with the deflecting voltage phase, on the contrary, the correlations between the particle energies and the vertical plane vary linearly with the deflecting voltage phase. The simulations are carried out by means of ELEctron Generation ANd Tracking (ELEGANT) code in the case of the Gamma Beam System (GBS) at the Extreme Light Infrastructure-Nuclear Physics (ELI-NP).