Slc Injector Simulation and Tuning for High Charge Transport

We have simulat.ed the SLC injector from the thermionic gun through the first accelerating section and used the resulting parameters to tune the injector for optimum performance and-high charge transport. Simulations-are conducted using PARMELA, a three-dimensional ray-trace code with a two-dimensional space-charge mod$The magnetic field profile due to the existing magnetic optics is calculated using POISSON, while SUPERFISH is used to calculate the space harmonics of the various bunchers and the accelerator cavities. The initial beam conditions inthe PARMELA code are derived from the EGUN modei-of the gun. The resulting injector parameters from the P_ARMELA simulation are used to prescribe experimental settings of the injector components. The. experimental results are in agreement with the results ofthe. integrated injector model.. Introduction The purpose of the SLC injector is to deliver two bunches of electrons to the damping ring at 1.2 GeV. The bunches of electrons are 61 nS apart, with greater than 6 x lo1 o electrons, in 20 ps per bunch, at the repetition rate of up to 120 Hz, with less than 2% intensity jitter. The SLC injector was designed ten years ago, using a one-dimensional, longitudinal, bunching code [l]. Although the injector has been operating reasonably satisfactorily since that time, to meet the requirements for steady, high-current operation we have modeled the entire injector in a consistently integrated way, using various codes of two or more dimensions for each portion, to improve its performance. This paper will address the modeling from the gun to the 40 MeV point in detail, followed by a discussion of experimental techniques used to achieve the high-current operation of the injector. Injector Simulation The SLC injector consists of two electron guns, each at a 38: angle from the accelerator centerline; a switching magnet to allow the operation of either gun; a bunching section consisting of two subharmonic bunchers (SHB) at 178.5 MHz separated by 108 cm; a 4-cell, 8 = .75 S-band (2856 MHz) bumher;-and a 3m, traveling-wave, S-band accelerating section-with 8&I, which contributes to bunching as well as accelerating thseam to'40 MeV. The injector compresses the *Work supported by Department of Energy contract DE AC03-76SF00515. 2.5 ns bunch from the gun to 20 ps at 40 MeV. Beyond 40 MeV there are a series of accelerating sections to accelerate the beam to 1.2 GeV. The radial growth of the beam due to space charge is controlled by the axial magnetic fields provided …