Electron Stretcher Facility ELSA
The electron stretcher facility (ELSA) includes an electron accelerator and various experimental facilities for basic research. The accelerator delivers a beam of polarized or unpolarized electrons with variable energy up to 3.5 GeV with a high duty cycle.
For the main research area of hadron physics currents of several nanoamperes can be extracted for single and double polarization experiments. As part of national and international collaborations, photo- and electro-produced final states of excited nucleons are examined using highly developed detectors with particular sensitivity for photon-rich states over large solid angle acceptances.
Since 2016 a dedicated beamline is available for testing detectors in high-energy physics, which delivers a direct electron beam with a maximum energy of 3.2 GeV. The extracted beam current can be varied over a wide range from attoamperes (a few kHz electron rate) up to 100 pA. Up to four measuring stations are available for internal and external users for irradiation experiments.
A significant part of the research activity at the ELSA accelerator is dedicated to the field of hadron physics. For this purpose two beamlines are available. A third beamline is used for the characterization of new particle detectors by both internal research groups (SILAB) and external groups. The same beamline is also used for fundamental research on novel methods of radiation therapy in cancer medicine.
Hadron Physics
Two collaborations in the field of hadron physics (Crystal-Barrel+TAPS and BGOOD) use sophisticated detector assemblies to study photoproduction of mesons at the accelerator facility.
Detector Development
At the accelerator facility, there is a measurement station where the extracted electron beam (up to 3.2 GeV) is used for the characterization of new particle detectors. The intensity of the electron beam can be precisely varied over a wide range from attoamperes (corresponding to an electron rate of a few kHz) to 100 picoamperes.
Medical Physics
For several years now, the accelerator has also been used for basic research in cancer therapy with usage of the high-energy (> 1 GeV) electron beams with short pulse duration (< 1 µs) in cancer therapy.
The accelerator facility is located partly in a hall next to the Physics Institute (booster synchrotron, hadron physics experiments), and partly in a tunnel under the buildings (stretcher ring). The booster synchrotron and the associated hall were built in the 1960s. The stretcher ring was added in the 1980s.
