The Electron Stretcher Accelerator

at the Physics Institute of the University of Bonn, Germany

Address Physikalisches Institut der Universität Bonn Nussallee 12 D-53115 Bonn Germany

Director Prof. Dr. F. Klein Tel.: +49-228-732340 Fax: +49-228-733518 email: klein@physik.uni-bonn.de

Contact persons for users

PD Dr. W. Hillert
Tel.: +49-228-733617
Fax: +49-228-733620
email: hillert@physik.uni-bonn.de

Short description of the facility:
The Electron Stretcher Accelerator ELSA is operated by the University of Bonn of the state Nordrhein-Westfalen. It consists of three stages (injector LINAC, booster synchrotron and stretcher ring) and provides a beam of polarized and unpolarized electrons with a tunable energy of up to 3.5 GeV. Internally a beam of 200 mA can be stored and used to deliver synchrotron radiation for material research and condensed matter physics. For the main research field of hadron physics currents of several nA (unpolarized) are extracted and sent to different experimental areas.
Large acceptance detectors for the spectroscopy of photo- and electroproduced final states have been set up, partially in international collaborations. They are well matched to the high duty factor of up to 90 % of the extracted beam. Leading expertise exists in the construction and operation of polarized solid state targets. Experiments have studied the photo-production of strange and non-strange mesons with the SAPHIR-detector. More recently the helicity-dependent absorption of GeV-photons by longitudinally polarized protons and deuterons has been measured in order to test the Gerasimov-Drell-Hearn-sumrule. Presently the focus is on the photo-excitation of baryon resonances studied in mesonic final states based on the Crystal Barrel detector with TAPS.
The work was supported by the Deutschen Forschungsgemeinschaft within the Schwerpunktprogramm "Untersuchungen der hadronischen Struktur von Nukleonen und Kernen mit elektromagnetischen Sonden" (SPP 1034).