Beam Position monitor for high intensity environments

STATEMENT OF THE PROBLEM 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. TECHNICAL APPROACH A novel diagnostic based on the well-established electro-optic sampling (EOS) technique is adaptable for non-interceptive position monitoring for high power beams. The electric fields that accompany relativistic, ultrashort bunches are used to diagnose both the beam bunch length 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 pulse. The measured response yields critical information on the beam temporal qualities. However, since the measured signal depends on the distance of the beam from the crystal surface, a multi-line EOS system laid out symmetrically about the beam centerline, can provide information on the position of the beam by analyzing the relative signal intensity on parallel arms of the system, which is the EOS-BPM configuration proposed herein. PHASE I PLANS The Phase I project aims to design a full three-dimensional version of the EOS-BPM. Preliminary experiments to test the proof-of-principle at the SLAC FACET-II facility are underway, under the leadership of University of Colorado Boulder. The team will participate in these experiments to gain firsthand operational experience on the diagnostic capability and data acquisition and interpretation. In parallel, engineering improvements will be applied, for the current version as well as forward-looking to the full three-dimensional version. These improvements include the development of pre-mounted, swappable crystals for rapid deployment in case of damage, or for parameter studies, schemes for independent control of laser alignment mirrors and crystal, and development of high-extinction ratio polarizers. The improvements will lay a foundation for Phase II, where a full 3-dimensional unit will be developed in a user-friendly package integrable into accelerator facilities. COMMERCIAL APPLICATIONS AND OTHER BENEFITS 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.