PHYSICS OF ELECTRON STORAGE RINGS: AN INTRODUCTION.

Abstract

Area of a transverse s'ection of a stored beam; o r amplitude of an oscillation, An effective area of colliding beams.Amplitude of an oscillation; invariant part of an ampl'it;ude.Time dilation of off-energy orbits (momentum compaction).' Damping coefficients of oscillations ( 1 / ~) ;. i = x, z , E .Magnetic field strength..-. Betatron functions., * Speed of light.2Energy in units of Pest erieriyy (~/mc-) . .Electron number per unit area (N/A) ; or rate of change of radiation loss with energy ( d ~/ d ~) .Half of the angle o l inlersection of colliding beams.E ~~C ~L ' U I I ~I I W ~Y .Nominal energy of a stored beam.Electric field strength.Electric charge of an electron.Frequency of revolution of a synchronous electron (c /L; c /27rR).Curvature function of the design orbit (l/,pB).Curvature of the design orbit of an ioomngnotio guide field (G6 = l / p d . Envelope function (J@.Off-energy fuhction, !Beam height.~e a m height a t the intersection.Beam current (Nef) .Partition numbers of the ditinping rates; i = x, z, E , Focussing functions of the guide field.Rf harmonic number (urf/ur); or deviation from nominal value of a focussing function (&Q.Length of the design orbit (27rR; c/f).Trajectory length; bunch length, Rest mass of an electron.Number of stored electrons in a beam (I/ef).Betatron number.Beam-beam interaction parameter.Radiofrequency power.Electron momentum'.Quantum excitation strength.Rf overvoltage ( e v / ~d .Gross radius of the design orbit (~/272). 2Classical electron radius (e /4n s omc ) .Radius of curvature of the design orbit a t s [ l / ~( s ) ] .Magnetic radius in an isomagnetic guide field.Azimuthal (longitudinal) coordinate.Standard deviation of a distribution.Time for a revolution, Revolution period of a synchronous electron (L/c).Laboratory time.Time displacement between an electron and the center of its bunch (y/c),Damping time constant of an oscillation mode (i/a i)Phase variable of betatron oscillations.Pseudopotential energy of the longitudinal oscillations.Energy loss by radiation in one revolution.Energy of a radiated quantum.Effective "voltage" of the rf system.Beam width.~e a m ' width a t the intersection.IIorizoi~tal (radial) dinplaccmont from tho doaign orbit, Longitudinal (azimuthal) displacement from a bunch center (cz) Vertical (axial) displacement from the design orbit.Angular frequency of the energy (and longitudinal) oscillations.Angular frequency of revolution ( P T / T ~ .Angular frequency of a betatron oscillation (v wr) p). I. AN INTRODUCTORY OVERVIEW1.1.Opening Remarks Electron storage rings have now come of age.With the successful operation of Adone, ' experiments will now begin using colliding beams of electrons and positrons with energies of 1 GeV and beyond, expanding the a r e a of storage ring research which was begun a t lower energies with the pioneering instruments at Stanford, Frascati, Novosibirsk, and Orsay.Projects under way at Novosibirsk, Cambridge, Hamburg, and Stanford will soon provide stored colliding beams of electrons a t even higher energies.L a r g e r numbers of workers will be basing their research in particle physics ori these instruments.Many of the physicists who will be using storage rings will not have had a part in their design and construction, and will not initially have a knowledge of their inner workings.The aim of this report is to provide for such physicists a review of the basic physical processes that determine the behavior of electron storage ringswith a particul a r concern for their performance a s instruments for research in particle physics.Because of this aim, the material is generally not presented in the form which might Be most convenient for 'those who will be interested in the design of storage rings.It is, rather, developed in a form intended to give the using physicist an understanding of the inherent properties of his instrumentespecially those which will have an influence on his observationsand to give him some feeling ' for its basic limitations and its ultimate capabilities.In the r e s t of this introduction I give a qualitative description of each of the basic phenomena that play a role in colliding beam storage rings, including a discussion of the factprs which determine the luminosity.This f i r s t part is intended to provide a background and a vocabulary for the appreciation of the other reportst which describe the operating experience with existing rings and the projects for new rings.In the remaining parts I shall consider in detail the theory of those basic single particle processes which determine the ultimate limits on the performance of storage rings.A. discussion of the important collective effects, which have lead to many practical difficulties in high intensity rings, isnot ---'other "reports" mentioned here refer to other contributions a t the Varenna Summer School of 1969.