Synchrotron

The synchrotron (of sync, "simultaneously" ) is a type of particle accelerators and belongs to the ring accelerators. Charged elementary particles or ions can it be accelerated to very high ( relativistic ) speeds, which gives them very high kinetic energies. Synchrotrons were designed to get beyond the reach of cyclotrons energies.

A special form of the synchrotron is the memory ring. The synchrotron can even after the particles are accelerated to a desired energy can be operated as a storage ring. Also a complete system from a storage ring and a separate synchrotron to its filling is sometimes simply referred to as synchrotron.

• 5.1 synchrotron
• 5.2 Some electron synchrotrons

• 6.1 Some ion synchrotron facilities

History

The basic concepts for the synchrotron independently developed in Russia by Vladimir Iosifovich Weksler (1944 at the Lebedev Institute) and Edwin McMillan ( during the Second World War in Los Alamos ). The first electron synchrotron was built in 1945 by McMillan, the first proton synchrotron 1952 by Mark Oliphant.

Principle and Design

A synchrotron consists of individual deflecting and mounted therebetween acceleration distance, in which the particle track is straight. The particle path is spiral as in a cyclotron or betatron, but extends from the beginning to the end of the acceleration process as a closed ring. The field of the deflection magnets as the magnetic field can not therefore remain constant over time in the cyclotron, but each particle bunch has to be increased in proportion to increasing particle momentum during acceleration. To speed are high-frequency alternating electric fields in cavity resonators. So that the particles are not lost by collisions with gas molecules is the web - as with any accelerator - in a ring tube in which a vacuum, more ultra-high vacuum (UHV ) prevails.

A synchrotron is not accelerating the particles " from scratch ", but is always fed by a pre-accelerator (injector ), which, for example, already brings to 20 or 50 MeV. Is it light particles such as electrons, they then pass already at near-light speed into a synchrotron. There are increased, as described by the relativistic mechanics, their energy and momentum, but practically no longer the speed; the frequency at which the current of the magnets is modulated, and the phase of the acceleration sections to one another can therefore be constant. For heavy particles like protons, however, the rate increases also in the synchrotron self too much. Here, therefore, each of the magnetic particle bunch other than the modulation frequency also has to be gradually raised during the acceleration, and also the synchronization ( phase shift ) of the high -frequency voltages of the individual resonators to be adjusted continuously.

Because of this major technical differences synchrotrons are always special

• Either for electrons / positrons
• Or built for protons (and possibly even heavier ions ).

Uses

In synchrotrons accelerated ions are generally used to collision or the target particle physics experiments basic research and in some cases also for therapeutic purposes. In contrast, we used electron storage rings today (2013 ) mainly as sources of synchrotron radiation; serve this purpose most of today's existing synchrotron facilities.

Achievable energy

The particle, which can be achieved in a given synchrotron is dependent on the maximum magnetic flux density B, the radius r of ( here assumed to be simplified circuit) and the ring of the particle. Approximation is valid for high energies:

Here q is the charge of the accelerated particle and c is the speed of light. In the formula, no dependence on the mass of the particle can be seen; However, the speed and thus the delivery of synchrotron radiation was not observed. Lighter particles are faster than heavier particles at the same energy and therefore emit more. The energy loss due to this radiation must be compensated by the electrical acceleration.

Strong focus

The particles cause during the revolution inevitable from oscillations ( so-called betatron oscillation ) around its nominal orbit. The amplitude of these oscillations determines the " thickness" of the beam so that the necessary width of the magnetic pole and so the overall size and construction costs. Therefore synchrotrons for energies above about 10 GeV on the principle of strong focusing: Bending magnets have alternately beveled pole pieces on both sides, so that the magnetic fields are transverse to the particle flight direction gradient with alternating direction. This results in a stabilization ( focusing) of the particle trajectories. In terms of the deflection of a particle in the transverse direction corresponds to it vividly the series arrangement of converging and diverging lenses for light, with a focus than net effect. The idea came from Ernest Courant, Livingston and Hartland Snyder in the U.S. ( and independently ago by Nicholas Christofilos ). Only then succeeded at CERN ( Proton Synchrotron, PS, 1960) and Brookhaven ( Alternating Gradient Synchrotron AGS, 1960), the construction of proton synchrotrons in the 30 GeV range and about the same time of electron synchrotrons with about 6 GeV at MIT and DESY. Today's (2013 ) largest synchrotron facility Large Hadron Collider has protons accelerated up to 4 TeV.

Instead of changing the gradient of the deflection magnetic fields strong focusing can be achieved outside of the bending magnets with quadrupole lenses.

Electron Synchrotron

Because the radiation loss at relativistic speeds with the fourth power of the energy increases (see # synchrotron radiation generation ), electrons in the synchrotron leave only up to about 10 GeV reasonably economical speed (though 1999 were achieved with the investment LEP 100 GeV ). Even faster electrons are produced cheaper with linear accelerators. In the now almost exclusive use of electron synchrotron as a radiation source electron energies are used up to about 6 GeV.

The electron synchrotron, a hot cathode electron source generates free electrons, which are then passed through a DC - acceleration section in a linear accelerator, a microtron or even into a first synchrotron accelerating ring. In this, the electrons are accelerated to their final energy and then - stored in a storage ring, which can have up to several hundred meters in circumference - in the case of a storage ring facility. The electrons are kept there until they are reduced by collisions with residual gas molecules under the usable density. In modern electron synchrotrons BESSY as ESRF or the lifetime of the electron current in the storage ring is a few days; However, electrons are supplied, to provide a sufficient annular flow continuously at regular intervals.

Synchrotron

An electron synchrotrons for the first time the intense and wide-band electromagnetic radiation in the spectral range of the X-ray and ultraviolet radiation ( synchrotron radiation ) was detected, which arises due to the distraction of very fast charged particles and the particles thus removes kinetic energy. She was described in 1949 by Julian Schwinger theory. First she went to electron synchrotrons for particle physics research disruptive in appearance; their excellent suitability for investigations in other areas of physics and other natural sciences, but also for industrial and medical applications was recognized only gradually. It is therefore now being produced deliberately. These are no longer required to guide the particle dipole magnet are used but additionally installed devices, the undulators.

Some electron synchrotrons

• ALS ( Advanced Light Source ), Lawrence Berkeley National Laboratory, Berkeley, USA
• Advanced Photon Source, Argonne National Laboratory in the USA
• ANKA ( Karlsruhe Angströmquelle )
• BESSY ( Berlin Electron Storage Ring Society for Synchrotron ) in Berlin ( at WISTA Adlershof )
• CLS (Canadian Light Source )
• DELTA ( Dortmund electron storage ring facility )
• DESY ( Deutsches Elektronen -Synchrotron Research Center )
• Diamond ( Diamond Light Source ), South Oxfordshire, UK
• ELETTRA ( ELETTRA Synchrotron Light Laboratory) in Trieste, Italy
• Electron Stretcher Accelerator (ELSA ) University of Bonn
• ESRF ( European Synchrotron Radiation Facility ) in Grenoble
• LNLS ( Laboratório Nacional de Luz Síncrotron ) in Campinas, State of São Paulo, Brazil
• MAX -LAB (MAX -LAB Synchrotron Radiation Facility ) in Lund, Sweden
• MLS ( Metrology Light Source) in Berlin, Germany
• NSLS ( National Synchrotron Light Source ) at Brookhaven National Laboratory, Long Iceland, USA
• SESAME ( Synchrotron -light for Experimental Science and Applications in the Middle East) in Allaan, Jordan
• SOLEIL ( Synchrotron SOLEIL ) in Gif -sur- YVETTE, in Paris, France
• SSRF in Shanghai
• SLS ( Swiss Light Source) at the Paul Scherrer Institute in Switzerland
• SSLS (Singapore Synchrotron Light Source at the National University of Singapore )
• UVSOR II ( Ultraviolet Synchrotron Orbital Radiation Facility ) in Okazaki, Japan

Synchrotron facilities for ion

The attainable energy ions is given in Modern synchrotron mainly to the above formula through the radius and the magnetic flux density. Since the achievable in large magnet flux density is limited to a few Tesla, synchrotrons for very high energies must necessarily have large radii. In the Large Hadron Collider at about 4.2 km radius are protons to 4 TeV ( tera-electron volts), has been so accelerated 4000 GeV; Expansion to 6.5 TeV is provided.

Some ion synchrotron facilities

• Tevatron in USA (2011 decommissioned)
• Nuclotron in Dubna (Russia)
• CERN -PS, ISR, LHC at CERN ( Conseil Européen pour la French Nuclear Research, European Nuclear Research Center ) near Geneva, Switzerland
• J- PARC in Japan
• COSY ( Cooler Synchrotron Research Centre Jülich )
• SIS18 and ESR at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt
• HIT ( Heidelberg Ion -Beam Therapy ), University Hospital Heidelberg