Photon Based Electron Beam Analysis at ELSA Utilizing Synchrotron Radiation and Compton Scattering

Within the collaborative research center SFB/TRR 16 "subnuclear structure of matter" the beam diagnostic capabilities of the ELSA storage ring at the Physics Institute of Bonn University have been extended by a synchrotron radiation beamline with a fast optical recorder for three-dimensional photometry of the electron beam and by a laser Compton backscattering polarimeter for monitoring the polarization degree of the stored electrons. The hardware performance of both beamlines allows extensive analysis procedures and parameter monitoring for the improvement of the accelerator's operation. The M7 photon beamline utilizes visible synchrotron radiation and enables the visualization of the electron beam with up to single bunch resolution. It allows simultaneous monitoring of the horizontal, vertical and longitudinal electron beam profile at multiple observation field spans from 3.1 to 28 mm within time frames of 74 ps to 100 ms. The visualization and measurement quality of important accelerator parameters - such as beam size, tune, damping times, bunch length and filling pattern - are demonstrated. It is observed that the numerical image analysis shows limits of validity in some cases, concerning measurements of the transverse beam size and bunch length. Dynamic beam behavior is, however, well observable and quantifiable. Beam properties such as the storage ring tune and the filling pattern homogeneity can be accurately determined through transverse and longitudinal images of the electron beam. At the Compton polarimeter beamline circularly left and right polarized photons from a continuous wave laser source scatter off the stored electrons. The vertical profiles of the backscattered gamma-photons are digitized by an in-house developed silicon microstrip detector and the electron beam polarization is determined through the shift in the means of profiles obtained from left and right circularly polarized photons. For profile quality enhancement a Pearson type VII peak function fit has shown to increase the measurement accuracy significantly. The polarimeter's analyzing power was obtained through the observation of the Sokolov-Ternov self-polarization effect and was determined to amount (61.2 +/- 8.9) µm / 100 % at 2.73 GeV beam energy. A statistical measurement accuracy of 2 % could be obtained within 5 minutes of measurement time and 1.4 % within 15 minutes. Compton polarimeter measurements of source-polarized electrons were able to resolve known spin dynamical effects occurring in the ELSA storage ring such as crossings of integer resonances and spin rotation through the application of solenoid magnetic fields. The polarimeter data was acquired within a limited testing period between October 2016 and January 2017

Beam and spin dynamics in the fast ramping storage ring ELSA: Concepts and measures to increase beam energy, current and polarization

The electron accelerator facility ELSA has been operated for almost 30 years serving nuclear physics experiments investigating the sub-nuclear structure of matter. Within the 12 years funding period of the collaborative research center SFB/TR 16, linearly and circularly polarized photon beams with energies up to more than 3 GeV were successfully delivered to photoproduction experiments. In order to fulfill the increasing demands on beam polarization and intensity, a comprehensive research and upgrade program has been carried out. Beam and spin dynamics have been studied theoretically and experimentally, and sophisticated new devices have been developed and installed. The improvements led to a significant increase of the available beam polarization and intensity. A further increase of beam energy seems feasible with the implementation of superconducting cavities

Beam and spin dynamics in the fast ramping storage ring ELSA: Concepts and measures to increase beam energy, current and polarization

The electron accelerator facility ELSA has been operated for almost 30 years serving nuclear physics experiments investigating the sub-nuclear structure of matter. Within the 12 years funding period of the collaborative research center SFB/TR 16, linearly and circularly polarized photon beams with energies up to more than 3 GeV were successfully delivered to photoproduction experiments. In order to fulfill the increasing demands on beam polarization and intensity, a comprehensive research and upgrade program has been carried out. Beam and spin dynamics have been studied theoretically and experimentally, and sophisticated new devices have been developed and installed. The improvements led to a significant increase of the available beam polarization and intensity. A further increase of beam energy seems feasible with the implementation of superconducting cavities