- ENERGY MATCHING OF 1 . 2 GEV POSITRON BEAM c TO THE SLC DAMPING RING

Positrons collected at the SLC positron source are transported over a 2-km path at 220 MeV to be reinjected into the linac for acceleration to 1.2 GeV, the energy of the emittance damping ring. Since the positron bunch length is a significant fraction of a cycle of the linac-accelerating RF, the energy spread at 1.2 GeV is considerably larger than the acceptance of the linac-toring (LTR) t ransport system. Making use of the large pathlength difference at the beginning of the LTR due to this energy spread, a standard SLAC 3-m accelerating section has been installed in the LTR to match the longitudinal phase space of the positron beam to the acceptance of the damping ring. The -design of the matching system is described, and a comparison of operating results with simulations is presented. INTRODUCTION The positron source for the Stanford Linear Collider (SLC) was designed to produce within the acceptance of the positron damping ring (DR) in excess of two positrons for every high-energy electron hitting the production area of the positron target.l During the initial commissioning of the source,2 the maximum yield (ratio of positrons at a given location to electrons hitting the positron production target) at the interaction region was only about 0.5, with typical values being in the region of 0.35 e+/e-. In Fall 1988, the SLC underwent a major upgrade to improve the overall performance of the collider. For the positron source, the improvements included an increase in the RF capture accelerating gradient from 18 to 40 MeV/m, installation of an energy-matching RF accelerating section in the LTR, and an extensive study of the beam optics to permit the magnet system to be run at model values. Presented at the XIV International Conference on High Energy Accelerators, Tsukuba, Japan, August 22-26, 1989. * Work supported by Department of Energy contract DE-AC03-76SF00515. J. E. CLENDENIN, R. H. HELM, R. K. JOBE, A. KULIKOV, and J. C. SHEPPARD TheFe improvements have doubled the yield of positrons at the interaction region, .with typical (maximum) values now at 0.7 (0.9) e+/eat 60 Hz. In what follows, f the design and performance of the energy matching section in the LTR is described. -. A sketch of the SLC is shown in Fig. 1. The transport line between the l-GeV linac and the e+ DR was designed with an energy acceptance of &l.S%. Originally this was to be the defining energy acceptance of the DR, but the dynamic energy acceptance of the DR has been measured to be more like &l%. In principle, as will be shown, this acceptance should be adequate, but, in fact, it is smaller than the actual energy spread of the beam. Consequently, as much as a factor of 2 was being lost in charge between the l-GeV linac and the DR.