Beam position monitor for high intensity environments

High-quality beam transport through wakefield acceleration schemes, such as plasma or structure-based, requires careful characterization of the transverse beam centroid position. The centroid position is particularly important as drive-witness centroid mismatches yield emittance growth compromising beam quality. Further, beam characterization at high power and high intensity, requires non-invasive, shottagged measurements to stabilize beam quality through the interaction. A novel diagnostic based on electro-optic sampling (EOS) is adaptable for non-interceptive position monitoring for high power beams. The electric fields of the relativistic, ultrashort bunches are used to diagnose both the centroid and the time-of-arrival on a shot-to-shot basis. In EOS, the electric field near a birefringent crystal induces a change in polarizability, which is probed by a low-energy laser. The response yields information on the beam temporal qualities. However, since the signal depends on the distance of the beam from the crystal, a multi-line EOS system laid out symmetrically about the beam centerline, can provide information on beam position by analyzing relative signal intensity on parallel arms. This configuration is called the electro-optic sampling beam position monitor (EOS-BPM). University of Colorado Boulder participated in experiments to test the proof-of-principle of a prototype 2D EOS-BPM at the SLAC FACET-II facility. The team gained first-hand operational experience on the diagnostic capability and data acquisition. In parallel, we designed a customized swappable crystal holder and solved other various issues. The holders were built, tested, and optimized through several iterations that led to a design of a 2D EOS-BPM. The principle was extended to design a prototype EOS-BPM capable of time of arrival and beam position monitoring along the two-transverse axis of the electron beam. A prototype version of the EOS-BPM was built and validated at RadiaBeam using GaP crystals. In Phase II, we will build off the results of Phase I and continue to refine the design with studies performed by both FACET-II facility and RadiaBeam teams, and conduct bench tests to further validate the design. The comprehensive package will include mechanical design and engineering of the optical system, and integration and tests at FACET-II facility. The ancillary work includes selection of the laser and redundant diagnostics providers, as well as development of user-friendly controls. The program results will yield a compact beam position monitor that can be used for high power and high intensity beams, and as an added feature, can also relay the beam longitudinal profile simultaneously. The utility of the device extends from high energy physics machines to light sources and synchrotrons.