The Stanford Storage Ring -spear*

SPEAR (Stanford Positron-Electron Asymmetric Ring) consists of a single ring of magnets threaded by an aluminum vacuum chamber in which counterrotating beams of electrons and positrons will circulate. A high luminosity is achieved by making the beams collide in one of two long 71low-beta71 interaction regions. 132 The ring is composed of the two matched low-beta regions connected by nearly circular arcs of unequal length3 (see Fig. 1). In its initial configuration SPEAR is limited to a maximum operating energy of about 2.5 GeV each beam by the rf voltage capability of the single cavity which will be installed in the ring. The magnets of the ring are however, designed to operate at energies up to 4.5 GeV, and an increase in the initial maximum operating energy thus requires an increase in the number of rf cavities and in the magnet power. The ring will operate in the so-called one-bunch mode wherein a single circulating bunch of electrons and a single bunch of positrons will collide with zero crossing angle at one of the two low-beta regions. The other potential collision point, because of the asymmetric design of SPEAR, is not at the (To be printed in the Review ‘Xerntechnik”t)