The electron stretcher facility ELSA is operated by the Physikalisches Institut of the University of Bonn and the state of North Rhine-Westphalia. It comprises an electron accelerator as well as experimental facilities to study the resonance structure of protons, neutrons and mesons. The actual accelerator consists of three stages (injector-LINAC, booster-synchrotron and stretcher-ring) and delivers a beam of polarized or unpolarized electrons with variable energy of max. 3.5 GeV and high duty cycle. An internal beam of max. 200 mA can be stored, which was used for (now discontinued) synchrotron radiation experiments in the field of materials research and solid state physics.
Research at the Electron Accelerator
ELSA
For the main research area of hadron physics, currents of several nA can be extracted and transferred to the different experimental sites. Within national and international collaborations, sophisticated detectors with special sensitivity for photon-rich final states over large solid angle acceptance have been put into operation for spectroscopy of photo- and electroproduced final states: Crystal Barrel with TAPS and BGO-Ball with magnetic spectrometer. The expertise available locally and with partners for the design and integration of polarized solid-state targets into the setups allows the performance of highly selective double polarization experiments to study the excitations of baryon resonances with high-energy photons. The ELSA facility formed the core of the DFG Collaborative Research Center SFB/TR 16 (Electromagnetic Excitations of Subnuclear Systems), which dealt experimentally and theoretically with baryon resonances.
Working groups and experiments at ELSA
Polarized Target
The polarized target is an experimental device for studying spin-dependent properties in particle physics. It consists of several individual components which can be used to dynamically align the spin of nucleons in a solid body (target material) at low temperatures and high magnetic fields. The working group "Polarized Target Bonn" is involved in the development and construction of individual components as well as the operation of the target apparatus at various scattering experiments at ELSA in Bonn, MAMI in Mainz and COSY in Jülich.
Test Beam at ELSA
For the test of high-energy physics detectors, a dedicated beamline has been available since the end of 2016, delivering a direct electron beam with a maximum energy of 3.2 GeV. The extracted beam current can be varied in a wide range from attoampere (few kHz electron rate) up to 100 pA.