Storage ring

Scheme of an electron-positron storage ring for high-energy physics experiments

Acceleration section of the ion storage ring ESR of GSI , Darmstadt

Section of the ESR of the GSI

A storage ring is a special form of a synchrotron - particle accelerator , specializing in the collection and long maintain a high beam current. It consists of a ring-shaped vacuum vessel in which high-energy , electrically charged particles are held in a closed orbit by magnets .

A storage ring is usually filled using a separate particle accelerator; However, a synchrotron can also function as a storage ring itself, in that the acceleration voltage is almost or completely switched off and the field of the deflecting magnets is kept constant. Some systems can therefore be referred to as synchrotron as well as storage ring.

Usually, many particle packets from the accelerator are collected in the storage ring (hence the name "storage"), so that the intensity in the storage ring is much higher than in the accelerator beam. In large systems, beam currents of several amperes were generated. To achieve a long dwell time of the jet in the storage ring, sometimes many hours, an extremely good vacuum is necessary, since collisions with the residual gas reduce the jet strength and also impair the jet quality. An exit of the beam from the ring for experimental purposes is either not intended or is of secondary importance. There are storage rings for electrons and a wide variety of ions , from protons and antiprotons to heavy ions such as gold and lead .

Generation of synchrotron radiation

Electron storage rings are often operated primarily or exclusively for the purpose of generating synchrotron radiation . To increase the intensity of the synchrotron radiation, special components are installed, the so-called wigglers or undulators ; these bring the electrons into a wavy line on an otherwise straight track section and thus lead to increased emission of radiation. The radiation losses are compensated for in the acceleration sections.

Collider

A special form of storage rings are the so-called Accelerator (engl. Collide : collide), which are usually constructed of two rings with opposite direction of rotation. The particles are brought to collision at one or more intersection points. In this way, unlike when bombarding a stationary target , the entire kinetic energy can be converted into the mass of new particles, because no kinetic energy is required for the center of gravity of the particle system to move further (see colliding beam experiment ).

Even with this use, the problem of all circular accelerators, the loss of energy due to synchrotron radiation , occurs for high-energy light particles such as electrons . New concepts for high-energy electron colliders therefore provide for two linear accelerators directed against one another, such as B. at the planned International Linear Collider .

Physical basics

A charged particle of mass m and charge q , moving with speed in a magnetic field of flux density , is forced onto a circular path with radius r by the Lorentz force . If you equate Lorentz force and centripetal force , you can solve the resulting equation and determine the diameter of the circular path. ${\displaystyle v}$ ${\displaystyle {\vec {B}}}$ ${\displaystyle {\vec {F}}_{L}=q\cdot {\vec {v}}\times {\vec {B}}}$ ${\displaystyle F_{Z}={\frac {m{\vec {v}}^{2}}{r}}}$ ${\displaystyle r}$

Storage ring locations

Storage rings can be found

• at CERN near Geneva
  • LHC - Large Hadron Collider (scope: 27 km, planned center of gravity : 14  TeV , commissioning November 2009)
  • LEP - Large Electron Positron Storage Ring (circumference: 27 km, highest center of gravity energy achieved: 209 GeV, operation 1989 to 2000)
  • Intersecting Storage Rings (circumference approx. 940 m, main energy: 56 GeV, operation 1971 to 1984)
• at the Paul Scherrer Institute in Villigen
  • SLS - Swiss Light Source; Synchrotron light source (circumference: 288 m, energy 2.4 GeV, 400 mA top-up; in operation since August 1, 2001)
• Synchrotron SOLEIL in Saint Aubin near Paris
• on the WISTA site in Berlin
  • BESSY II at the Helmholtz Center Berlin for Materials and Energy (HZB) (circumference 240 m, energy 1.7 GeV)
  • MLS (Willy Wien Laboratorium) of the Physikalisch-Technische Bundesanstalt (PTB) (circumference 48 m, energy 200 - 600 MeV)
• at the Karlsruhe Institute of Technology (KIT)
  • ANKA - Ångströmquelle Karlsruhe (circumference 100 m, energy 2.5 GeV)
• at the Technical University of Dortmund
  • DELTA - Dortmund electron storage ring system (115.2 m)
• at the German Electron Synchrotron (DESY) in Hamburg
  • DORIS - double-ring storage (circumference: 300 m, energy 4.6 GeV, operation 1974 to 2012)
  • PETRA - Positron Electron Tandem Ring Accelerator (scope: 2.3 km, maximum center of gravity: 47 GeV, operation as a collider from 1978 to 1986, operation as a synchrotron radiation source from 2009)
  • HERA - Hadron Electron Ring Accelerator (length: 6.3 km, operation 1991 to 2007)
• at the Fermi National Accelerator Laboratory (Fermilab) near Chicago
  • Tevatron - proton-antiproton accelerator (circumference: 6.3 km, center of gravity: 1.96 TeV, operation 1983 to 2011)
• at the European Synchrotron Radiation Research Center ESRF in Grenoble (circumference 844 m)
• at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt
  • ESR - experimental storage ring
• at the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg
  • TSR
  • CSR
• at the Stanford Linear Accelerator Center (SLAC) at Stanford University
  • PEP-II

literature

F. Hinterberger: Physics of Particle Accelerators and Ion Optics. 2nd edition, Springer 2008, ISBN 978-3-540-75281-3

Individual evidence

1. ^ K. Johnsen: CERN Intersecting Storage Rings (ISR) . In: Proc. N / A. Acad. Sci. USA . 70, No. 2, 1973, pp. 619-626. PMC 433316 (free full text).
2. ↑ http://www.fnal.gov/pub/tevatron/index.html