First difference mode interferometer demonstration for a high-bandwidth Electro-Optic Beam Position Monitor

This work presents, for the first time, the experimental demonstration of the differential-field detection mode Δ as a key component in the ongoing development of a novel interferometric Electro-Optic Beam Position Monitor (EO-BPM), capable of high-bandwidth monitoring of 1\,ns -long HL-LHC ultra-relativistic proton bunches. Through the utilization of an innovative fibre-coupled Mach-Zehnder detection scheme, in its first experimental implementation, this study proves that the new field-focusing pickup design engineered to facilitate long-distance and high-bandwidth single-pass detection can deliver a sub-millimetric detection resolution while keeping an ultrafast time response below the HL-LHC goal of 50\,ps . The transverse-position and time-resolution capability of the system were addressed at HiRadMat and CLEAR beamlines, respectively. The transverse position study was performed within a ± 20\,mm range at 3\,GHz acquisition bandwidth for SPS-like parameters ( 4σ ≈ 1.5\,ns\, & \,1.2× 10¹¹p⁺ ), whereas a 33\,GHz response was achieved by detecting short CLEAR electron bunches ( 4σ ≈ 20\,ps ). In addition, the stability of the signals acquired under high levels of back-scattering radiation also proves that, due to the optical nature of the device, the EO-BPM differential-field mode is unaffected, and therefore very suitable for such environments.