The DESY (Deutsches Elektronen Synchrotron, "German Electron Synchrotron") is the biggest German research center for particle physics, with sites in Hamburg and Zeuthen.
DESY's main purposes are fundamental research in particle physics and research with synchrotron radiation. For this DESY develops and runs several particle accelerators. DESY is financed by the public authorities and is a member of the Helmholtz Association of National Research Centres.
DESY was founded on December 18, 1959 in Hamburg by means of a treaty signed by the federal minister for atomic energy Siegfried Balke and Hamburg's mayor Max Brauer.

Functions
DESY consists of two sites, a larger one in Hamburg, a smaller one in Zeuthen, both in Germany.

Sites
The DESY site in Hamburg is located in the west of the city and is bounded by the ring of the particle accelerator PETRA. A part of the larger HERA (Hadron Elektron Ring Anlage) ring runs through the site, but most of the 6.3 km of the ring run under the "Altonaer Volkspark".
At the site in Hamburg most of DESY's research in high energy physics with elementary particles has been taking place since 1960. Besides the already running accelerators there is also a free electron laser called XFEL being developed. This project is meant to secure DESY's future place among the top research centers of the world.

Hamburg
On January 1, 1992 DESY got a second site with the Institute for High Energy Physics at Zeuthen (Institut für Hochenergiephysik IfH).
DESY Zeuthen is currently contributing to the experiments at HERA in Hamburg for example by evaluating data. It is also collaborating with DESY Hamburg in the development of the XFEL.
Zeuthen is also participating in two in the context of DESY's research rather unusual projects:

For neutrino astrophysics DESY Zeuthen made some major contributions to the development of the neutrino telescope AMANDA, which was constructed in 1994 by scientists from all around the world at the South Pole.
Located in Zeuthen is the "Zentrum für Paralleles Rechnen", where several massive-parallel high-performance computers are run and used for example for calculations in theoretical particle physics. Zeuthen
The research center has an annual budget of ca. 160 mio € (=195 mio US-$). Of this, 145 mio € go to Hamburg, 15 mio € to Zeuthen. 90% of the budget is provided by the Federal Ministry for Education and Research, while the rest is provided by the state of Hamburg or Brandenburg respectively.
The experiments at the accelarators are financed by the participating German and foreign institutes, which in turn are often financed by means of public funding.

Budget and Financing
All in all 1560 people are employed at DESY, of which 365 are scientists. Those are distributed on the two sites as follows.
(date: January 2005)
Included in theses numbers are 100 apprentices as well as the 100 diploma students, 430 graduate students and 240 junior scientists who are supervised by DESY.

Hamburg: 1390 employees, thereof 300 scientists
Zeuthen: 170 employees, thereof 65 scientists Employees and Training
2900 scientists from 33 nations participate in the research at DESY. Hereof 1000 carry out research in particle physics at HERA, 1900 carry out research with synchrotron radiation at HASYLAB. (date: January 2005)

International Cooperation
The construction of the accelerator HERA was one of the first really internationally financed projects of this magnitude. Beforehand the construction of scientific facilities was always financed by the country in which it is located. Only the costs for the experiments were carried by the conducting national or foreign institutes. But due to the enormous scope of the HERA project many international facilities consented to already help with the construction. All in all more than 45 institutes and 320 corporations participated with donations of money and/or materials in the construction of the facility, more than 20% of the costs were carried by foreign institutions.
Following the example of HERA, many scientific projects of a large scale are financed jointly by several states. By now this model is established and international cooperation is pretty common with the construction of those facilities.

The International Project HERA
DESY's accelerators were not built all at once, but rather were added one by one to meet the growing demand of the scientists for higher and higher energies to gain more insight into particle structures. In the course of the construction of new accelerators the older ones were converted to pre-accelerators or to sources for synchrotron radiation for laboratories with new research tasks (for example for HASYLAB).
Nowadays DESY's most important facilities are the accelerator HERA, the synchrotron-research lab HASYLAB and the free-electron laser VUV-FEL, the test facility for the planned XFEL. The development of the different facilities will be described chronologically in the following section.

Particle Accelerators, Facilities and Experiments at DESY
The construction of the first particle accelerator DESY (Deutsches Elektronen Synchrotron, "German Electron Synchrotron"), whose name the institute is still bearing, began in 1960. At that time it was the biggest facility of this kind and was able to accelerate electrons to 7.4 GeV. On January 1, 1964 the first electrons were accelerated in the synchrotron and the research on elementary particles began.
The international attention first focused on DESY in 1966 due to its contribution to the validation of quantum electrodynamics, which was achieved with results from the accelerator. In the following decade DESY established itself as a center of excellence for the development and operation of high-energy accelerators.
The synchrotron radiation, which comes up as a side effect, was first used in 1967 for absorption measurements. For the arising spectrum there had not been any conventional radiation sources beforehand. The European Molecular Biology Laboratory EMBL made use of the possibilities that arose with the new technology and in 1972 established a permanent branch at DESY with the aim of analyzing the structure of biological molecules by means of synchrotron radiation.
The electron-synchrotron DESY II and the proton-synchrotron DESY III were taken into operation in 1987 and 1988 respectively as pre-accelerators for HERA.

DESY
DORIS (Doppel-Ring-Speicher, "double-ring storage"), built between 1969 and 1974, was DESY's second circular accelerator and its first storage ring with a circumference of nearly 300 m. Constructed as an electron-positron storage ring, one could conduct collision-experiments with electrons and their antiparticles at energies of 3.5 GeV per beam. In 1978 the energy of the beams was risen to 5 GeV each.
With evidence of the "excited charmonium states" DORIS made an important contribution to the process of proving the existence of heavy quarks. In the same year there were the first tests of X-ray lithography at DESY, a procedure which was later refined to X-ray depth lithography.
In 1987 the ARGUS detector of the DORIS storage ring was the first place where the conversion of a B-meson into its antiparticle, the anti-B-meson was observed. From this one could conclude that it was possible, for the second-heaviest quark - the bottom-quark - under certain circumstances to convert into a different quark. One could also conclude from this that the unknown sixth quark - the top quark - had to possess a huge mass. The top quark was found eventually in 1995 at the Fermilab in the USA.
After the commissioning of HASYLAB in 1980 the synchrotron radiation, which was generated at DORIS as a byproduct, was used for research there. While in the beginning DORIS was used only ⅓ of the time as a radiation source, from 1993 on the storage-ring solely served that purpose under the name DORIS III. In order to achieve more intense and controllable radiation, DORIS was upgraded in 1984 with wigglers and undulators. By means of a special array of magnets the accelerated electrons could now be brought onto a slalom course. By this the intensity of the emitted synchrotron radiation was increased a hundredfold in comparison to conventional storage ring systems.
DORIS III provides 42 experimental areas, where ca. 80 instruments are operated in circulation. The overall beam time per year amounts to 8 to 10 months.

DORIS III
PETRA (Positron-Elektron-Tandem-Ring-Anlage, "positron-electron tandem-ring facility") was built between 1975 and 1978. At the time of its construction it was the biggest storage ring of its kind and still is DESY's second largest synchrotron after HERA. PETRA originally served for research on elementary particles. The discovery of the gluon, the carrier particle of the strong nuclear force, in 1979 is counted as one of the biggest successes. PETRA can accelerate electrons and positrons to 19 GeV.
Research at PETRA lead to an intensified international use of the facilities at DESY. Scientists from China, England, France, Israel, the Netherlands, Norway and the USA participated in the first experiments at PETRA alongside many German colleagues.
In 1990 the facility was taken into operation under the name PETRA II as a pre-accelerator for protons and electrons/positrons for the new particle accelerator HERA. In March 1995, PETRA II was equipped with undulators to create greater amounts of synchrotron radiation with higher energies, especially in the X-ray part of the spectrum. Since then PETRA serves HASYLAB as a source of high-energy synchrotron radiation and for this purpose possesses three test experimental areas. Positrons are accelerated to up to 12 GeV nowadays.

PETRA II
The HASYLAB (Hamburger Synchrotronstrahlungslabor, "Hamburg Synchrotron radiation Laboratory") is used for research with synchrotron radiation at DESY. It was opened in 1980 with 15 experimental areas (today there are 42). The laboratory adjoins to the storage ring DORIS in order to be able to use the generated synchrotron radiation for its research. While in the beginning DORIS served only one third of the time as a radiation source for HASYLAB, since 1993 all its running time is available for experiments with synchrotron radiation. On top of the 42 experimental areas DORIS provides, there are also three test experimental areas available for experiments with high-energy radiation generated with the storage ring PETRA.
After the upgrade of DORIS with the first wigglers, which produced far more intense radiation, the first Moessbauer spectrum acquired by means of synchrotron radiation was recorded at HASYLAB in 1984.
In 1985 the development of more advanced X-ray technology made it possible to bring to light the structure of the influenza virus. In the following year researchers at HASYLAB were the first to successfully make the attempt of exciting singular grid oscillations in solid bodies. Thus it was possible to conduct analyses of elastic materials, which were possible prior to this only with nuclear reactors via neutron scattering.
In 1987 the workgroup for structural molecular biology of the Max Planck Society founded a permanent branch at HASYLAB. It uses synchrotron radiation to study the structure of ribosomes.
Nowadays many national and foreign groups of researchers conduct their experiments at HASYLAB: All in all 1900 scientists participate in the work. On the whole the spectrum of the research ranges from fundamental research to experiments in physics, material science, chemistry, molecular biology, geology and medicine to industrial cooperations.
One example is OSRAM, which since recently uses HASYLAB to study the filaments of their light bulbs. The gained insights helped to notably increase the life span of the lamps in certain fields of application.
In addition researchers at HASYLAB analysed among other things minuscule impurities in silicone for computer chips, the way catalysators work, the microscopic properties of materials and the structure of protein molecules.

HASYLAB
HERA (Hadron-Elektron-Ring-Anlage, "Hadron-Electron-Ring-Facility") is DESY's largest synchrotron and storage ring, with a circumference of 6336 metres. The construction of the subterranean facility began in 1984, and HERA began operation on November 8, 1990. The first two experiments started taking data in 1992. HERA is mainly used to study the structure of protons and the properties of quarks. HERA's construction was an international task: In addition to Germany 11 further countries participated in the development of the accelerator.
HERA is the first and only accelerator in the world that is able to collide protons with either electrons or positrons. To make this possible HERA used mainly superconducting magnets, which was also a world first. At HERA it was possible to study the structure of protons up to 30 times more accurately than before. The resolution covered structures 1/1000 of the proton in size. In the years to come there were made a lot of discoveries concerning the composition of protons from quarks and gluons.
HERA's tunnels run 10 to 25 metres below ground level and have an inner diameter of 5.2 metres. For the construction the same technology was used as for the construction of subway tunnels. Two circular particle accelerators run inside the tube. One accelerates electrons to energies of 27.5 GeV the other one protons to energies of 920 GeV in the opposite direction. Both beams complete their circle nearly at the speed of light, making approximately 47 000 revolutions per second.
At two places of the ring the electron and the proton beam can be brought to collision. In the process electrons or positrons are scattered at the constituents of the protons, the quarks. The products of these particle collisions, the scattered lepton and the quarks, which were produced by the fragmentation of the proton, are registered in huge detectors. In addition to the two collision zones there are two more interaction zones. All four zones are placed in big subterraneous halls. A different international group of researchers is at work in each hall. These groups develop, construct and run house-high, complex measurement devices in many years of cooperative work and evaluate enormous amounts of data.
The experiments in the four halls will be presented in the following section:

HERA
H1 is a universal detector for the collision of electrons and protons and is located in DESY's HERA-Hall North. It has been active since 1992, measures 12 m x 10 m x 15 m and weighs 2 800 tons.
It is designed for the decryption of the inner structure of the proton, the exploration of the strong interaction as well as the search for new kinds of matter and unexpected phenomena in particle physics.

ZEUS
HERA-B was an experiment in HERA-Hall West which collected data from 1999 to February 2003. By using HERA's proton beam, researchers at HERA-B conducted experiments on heavy quarks. It measured 8 m x 20 m x 9 m and weighed 1 000 tons.

HERA-B
The HERMES experiment in HERA-Hall East was taken into operation in 1995. HERA's longitudinally polarised electron beam is used for the exploration of the spin structure of nucleons. For this purpose the electrons are scattered at energies of 27.5 GeV at an internal gas target. This target and the detector itself were designed especially with a view to spin polarised physics. It measures 3.5 m x 8 m x 5 m and weighs 400 tons.
At the moment HERMES is able to conduct inclusive measurements (only for the scattered lepton) and semi-inclusive measurements (for the scattered leptons and some of the hadronic products). In the future the recoil-detector which was recently installed will enable researchers to conduct exclusive measurements (for all endproducts).

HERMES
VUV-FEL (Vacuum-Ultra-Violet Free-Electron-Laser) is a superconducting linear accelerator with a free electron laser for radiation in the vacuum-ultraviolet and soft X-ray range of the spectrum. VUV-FEL is based on the TTF (TESLA Test Facility), which was built in 1997 to test the technology that was to be used in the planned linear collider TESLA, a project which was replaced by the ILC (International Linear Collider). For this purpose the TTF was enlarged from 100 m to 260 m.
At the VUV-FEL technology for the future-project XFEL is tested as well as for the ILC. Five test experimental areas have been in use since the commissioning of the facility in 2004.
On April 6, 2006, the DESY Directorate has decided to change the name of the facility. The new name is FLASH.
FLASH stands for "F"reie-Elektronen-"LAS"er in "H"amburg or the equivalence in other languages.

Further Accelerators
DESY is involved in the project International Linear Collider (ILC). This project consists of a 20–40-kilometer-long linear accelerator. An international consortium decided to build it with the technology originally developed for the TESLA project. There has been no final decision on where to build the accelerator.
DESY is planning the construction of an X-ray laser, the XFEL (X-ray Free-Electron Laser), which is supposed to be 3 km long when finished. It will produce extremely short and powerful X-ray flashes which will have many applications.
Furthermore the accelerator PETRA, which is currently used as a pre-accelerator for HERA, shall be reconstructed as a source of synchrotron radiation for HASYLAB.