Single Wavelength Standard

A l)i planar wiggler has been designed that will be used for the initial operation of the 4-18 GeV storage ring PEP. Three of these wigglers will be installed symmetrically around the ring at 120° intervals in three of six available 5 m straight sections with the purpose' of providing: (1) beam size control to obtain better luminosities below 15 GeV, and (2) decreased damping times to obtain better injection rates at lower energies. Design goals are discussed and a description of the final system including cost estimates is given. Expected results and usage in PEP are discussed. Some possibilities for production of synchrotron radiation and beam monitoring with shorter wavelength, multiple-period wigglers at PEP energies are also discussed. Comparison to a wiggler now operating in SPEAR is given. II. Purpose Although many potential applications of wigglers have been known for a long time, there have been surprisingly few actual applications. The interested reader can consuit the proceedings of two recent con-ferences2*3 for a good overview of some possibilities as well as pitfalls. The usefulness of PEP for high energy physics depends on achieving acceptably high luminosities over as large an energy range as practicable. For a constant ring configuration, i.e., one in which the bending and focusing fields scale with momentum or energy, there will be a linear dependence of the transverse beam dimensions on energy because the synchrotron radiation integrals are basically unchanged (see below). This results in a maximum luminosity, pm,, which is expected to go as E4 whenever there is sufficient current to obtain the critical transverse particle densities1s4 determined by the incoherent beam-beam Interaction. When the maximum beam currents are limited by the beam-beam interaction, the maximum theoretical luminosity, Pat at any energy can only be attained when the transverse beam size Is Increased to the "limiting aperture" value. Wasted aperture therefore implies more time (funds) to achieve a given physics result for energies below the value at which the aperture is supposed to be filled, On the other hand, if the beam size can be kept'constant with decreasing energy, then-@LX will go as E2. Thus, since the aperture is designed for 15 GeV, a tunable variation in beam emittance-EX of at least (15/4)* is desired for operation down to 4 GeV. Such increases can be achieved using high-field wiggler magnets which increase-the quantum excitations of the beam as well as the damping and energy …