Design Study For The ELFA Linac W.A.Barlettal, G.Bellomo2, G. Gemmes, R. Parodi3, V. Stagno4, V. Variale” 1 Lawrence Berkeley Laboratory , USA, 2 INFN and Univ. of MilanJtaly 3 INFN Genova, Italy 4 INFN and Univ. of Bari, Italy Abstract The accelerator for ELFA must provide a 6 MeV electron beam to drive a single passfree electron laser at 100 GHz. The 1.3 GHz linac will operate at low repetition rate (10 Hz) and short macropulse (2 ns) and should provide peak current over 50 A. The envisaged accelerator includes a gridded electron gun, a prebuncher and a multicell bunching/accelerating section. The general characteristics of the accelerator and the expected performances, as evaluated by beam dynamics studies,are presented. I. Introduction ELFA (Electron Laser Facility for Acceleration) is a high gain, single pass free electron laser designed to operate in the microwave region (100 GHz) to explore fundamental FEL physics with short bunches. The project has been revised in 1992 to obtain a reduction in cost, schedule and technical risk while maintaining the physic goals of the original proposal. A detailed rewiew of the project is presentedelsewhereat this conference [ 11. The minimum beam characteristic satisfying the above requirements are reported in Table I. The micropulse length of 35 ps, corresponding to three optical wavelength of the 100 GHz radiation, implies the choice of a L-band (1.3 GHz) accelerator in order to minimize the micropulse energy spread. Table I- Beam parameters Nominal energy Peakcurrent Energy spread,rms Norm. rms emittance * micropulse length number of micropulses repetition rate * &ms = Pr ~x~x’ 6 MeV >50 A < 1% < 50 x mm mrad >35 ps 3 10 Hz II. The accelerator The specifications of table I can be easily met and exceeded by a photocathode RF gun of the type in operation at Los Alamos. It was felt however that a photocathodeRF gun requires a considerable staff effort to be developed and operated. Also, the cost and delivery time can be kept at minimum with a more conventional configuration. The preferenceis therefore versusa design that allows the option to buy a commercially available technology and to concentratethe efforts on the experiment. The design study has been focusedon an acceleratorwith . a gridded electron gun . a prebunching cavity at the fundamental frequency . a bunching/accelerating section A scheme of the accelerator is shown in fig 1. The main componentsare describedin the following. ION PUMP II I 111 IONPUMP 1 / 1 :,,H;~cm ,op, Fig. 1. Schematicview of the accelerator. 0-7803-1203-l/93$03.00 0 1993 IEEE © 1993 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. PAC 1993