Berlin electron storage ring society for synchrotron radiation
The Berlin Electron Storage Ring Society for Synchrotron Radiation mbH (BESSY) is the name of a research facility in Berlin that provided services for science and industry by providing synchrotron radiation . The operating company was founded on March 5, 1979 to set up and operate an electron storage ring system . On November 11, 2009, BESSY GmbH merged with the Hahn-Meitner-Institut (HMI), which had previously been renamed the Helmholtz Center Berlin for Materials and Energy (HZB) . As a result, BESSY GmbH left the Leibniz Association , the HZB is part of the Helmholtz Association .
The synchrotron light source BESSY II is operated at the Berlin-Adlershof location. Every year around 2000 external scientists come to BESSY II to carry out measurements there.
BESSY I
The 130 million D-Mark (equivalent to 66.5 million euros ) expensive BESSY I system went into operation on December 19, 1981 at Breitenbachplatz in Berlin-Wilmersdorf . BESSY I has had far-reaching scientific success in providing vacuum ultraviolet (VUV) and soft X-rays (XUV). The plant was shut down in 1999 in favor of BESSY II for cost reasons. Large parts of the facility were dismantled in 2001 and brought to Jordan as part of a UNESCO project, where they were reused as part of the SESAME project. The building now houses a branch of the Berlin-Brandenburg calibration office .
In BESSY I, electrons with a kinetic energy between 200 and 800 MeV (mega electron volts ) were stored. It was around 60 meters in circumference. With the help of BESSY I, the spectrometers of the Soho solar probe and the detectors of the Chandra space telescope were calibrated.
BESSY II
The success of BESSY I led to an increasing demand for synchrotron radiation, so that the decision was made for a more powerful radiation generator, a high-brilliance radiation source.
Construction of BESSY II in Berlin-Adlershof began on July 4, 1994, and BESSY II was inaugurated on September 4, 1998. The 200 million D-Mark (equivalent to 102 million euros) project consists of a synchrotron with a circumference of 96 meters as well as the actual electron storage ring with a circumference of 240 meters and an experimental hall.
Electrons are accelerated to a maximum energy of 1.7 GeV and injected into the storage ring. A maximum ring current of 300 mA is possible. Light pulses are generated on both deflection magnets and undulators . Depending on the type of deflection (undulator, wiggler or dipole), photon energies of up to about 15 keV can be achieved. The theoretical maximum of 1.7 GeV would only be reached if the electrons accelerated to this same energy were aimed at a target and slowed down; the bremsstrahlung would then have the expected 1.7 GeV (see how an X-ray tube works and the Duane-Hunt law ). The plant consumes 2.7 MW of electrical power in normal operation.
The PTB operates at BESSY several beamlines at which both undulator is generated and dipolbasierte synchrotron radiation and among other things, photon metrology used. Since the PTB often uses the BESSY to calibrate various types of light sources and detectors, the BESSY II is the European radiation standard in this context. Examples are the SUMER and CDS of the SOHO satellite for exploring the sun.
On September 24, 2004 work began on building the Metrology Light Source (MLS), also known as the Willy Wien Laboratory , a PTB project , in the immediate vicinity . This went into operation in spring 2008 and will, among other things, take on tasks similar to those of BESSY I. The MLS has a circumference of 48 meters.
There are different modes in which BESSY is operated. These differ in the time interval between the electron bunches:
- Multibunch : This is the operating mode that is most often used. There are about 350 equally filled electron bunches in the ring with a time interval of 2 ns between each other. A gap of around 100 ns is left between the packets, in which there are only four individual, but more filled, electron packets (together “hybrid filling”). These packets are used on a special beamline to generate very short light pulses. The synchrotron is normally in top up mode d. H. the filling of all packets is kept constant by continuous injection. ,
- Singlebunch : This operation is offered two weeks in the half-year. Here there is only a single electron packet in the ring. This mode is suitable for time-resolved experiments, since the time interval between two successive light pulses is 800 ns, so that they can be easily distinguished from one another.
- Low-alpha : In the low-alpha mode (both singlebunch and multibunch), the electron bunches are spatially strongly concentrated (with less filling), so that brief light pulses are generated. Furthermore, the emitted intensity in the terahertz range is much greater in this mode .
The future projects at BESSY II
BESSY II is continuously being further developed in order to improve the conditions for research and to deliver customized light pulses of the required quality. Important future projects for BESSY II are:
- BESSY VSR : BESSY II currently delivers a high photon flux with a fixed pulse length of 17 picoseconds in regular operation. Operation is switched over only a few days a year, so samples can also be examined with pulses of around two picoseconds. However, the flow of photons is greatly reduced. This is to change with the new BESSY VSR (variable pulse length storage ring) concept: the researchers can then freely determine the required pulse length on each individual beamline and for each experiment, without any loss of intensity. BESSY VSR thus closes the gap between storage rings such as PETRA III and free electron lasers.
- bERLinPro : This is about further developing a new type of accelerator technology. bERLinPro will now show that an electron beam of the highest intensity and density can be guided through a beam guidance system and then transported back to the linear accelerator in such a way that the electrons there return their energy to the field. The energy recovered from the beam is then available to accelerate a freshly generated electron beam - which in turn has the same excellent parameters as the beam from the previous cycle.
BESSY-FEL
From July 2000 the construction of a free electron laser (FEL) was planned. The approximately 400 m long linear accelerator was to be built right next to the BESSY II synchrotron on Ernst-Ruska-Ufer. Just like the ring accelerator, it should generate light pulses in the ultraviolet to soft X-ray range. However, these would be of higher intensity for a much shorter duration. A planned area of application is, for example, the investigation of chemical reactions, whereby the stroboscopic effect can be used to take snapshots of the complex processes.
In May 2006 the Science Council recommended the construction of the BESSY-FEL. From 2007 to 2010 a two-stage system was initially to be built and tested, which was then to be expanded into the four-stage BESSY-FEL from 2010.
In autumn 2008 it was decided not to build the FEL at BESSY II, but as an extension to the FLASH at DESY in Hamburg . BESSY II, on the other hand, aims to research a linear accelerator with energy recovery (ERL).
Web links
- Helmholtz Center Berlin for Materials and Energy GmbH
- Overview of the methods and experiments available at BESSY II
swell
- ^ Arnold, D .: "The BESSY electron storage ring as a standard radiation source for X-radiation and the determination of photon emission probabilities of radionuclides." Dissertation, TU Berlin 1991.
- ↑ BESSY II photon source. Helmholtz Zentrum Berlin, October 1, 2013, accessed on June 18, 2016 (BESSY II as a European radiation standard for the calibration of light sources and detectors).
Coordinates: 52 ° 25 ′ 40 ″ N , 13 ° 31 ′ 57 ″ E