. .? An Rf-Gun-Driven Recirculated Linac as Injector and FEL Driver ;;;] ,fg f>% ,% ~* . J~&be~~$~Q Ake Andersson, Mikael Eriksson, Sverker Werhd MAX-Laboratory, University of Lund, Lund, Sweden ~~~ 1~ &KJg Sandra Biedron ci?fj~l Argonne National Laboratory, Advanced Photon Source, Argonne, Illinois Henry Freund Science Applications International Corporation, McLean, Virginia A new pre-injector for the MXX-Laboratory is under design and constructwn. A therrnionic rf gun, designed to operate at medium currents with hw back bombardment power, is under construction. The gun will, via a magnetic compressor and energy jilter, feed a recirculated linac consisting of two SLED-equipped structures giving 125 MeV each. The jirst will be delivered in 1999. The system is aimed as a pre-injector for the m“sting storage rings at &MX-Lab, but will aLro open up possibilities for a SASE FEL in the W reaching above 100 MW below 100 run. Introduction The injector systems at MAX-Lab are currently being upgraded. The 100-MeV racetrack microtron [1] that currently feeds the two storage rings MAX I and MAX II will be replaced by a new injector system consisting of two 5.2-m, 3- GHz acceleration sections of the DESY II type [2] and a SLED system [3] . Each section will give an energy gain of 125 MeV and the two sections will be recirculated once to give a total of 500 MeV. The Iinacs will be injected tlom a newly designed 2.3-MeV thermionic rf gun. The total circumference of this system is 30 m or 100 ns. The electron gun is equipped with a fast kicker magnet that allows a 100-ns-long electron beam to be accelerated in the linacs. Apart from being used as a storage ring injector, the injection system will also open up new possibilities for its use as an electron source for a SASE (Self-Amplified Spontaneous Emission) FEL tunable from the IR to”the W spectml regions. 1. THE INJECTOR 1.1 Rf Gun The gun is a %+1%+1cell 3-GHz structure using a 6-mm-diameter cathode and having an input coupling hole and a plunger hole in the main cavity. The gun layout is shown in Figure 1. Figure 1. Gun layout Elm J (overall inner length 100 ~ maximum inner radius lMAX-Lab, P.O. Box 118, S-221 00 Lund, Sweden. Email: sverker.werin@maxlab.lu.se Fax: 46-46-2224710 40.69 The submitted manuscript has been created by the University of Chicago as Operator of Argonne National Laboratory (“Argonne”) under Contract No. W-31 -1 09-ENG-38 with the U.S. Department of Energy, The U.S. Government retains for itself, and others act- ing on its behalf, a paid-up, nonexclusive. irrevocable worldwide license in said article to reproduce, prepare derivative works, dis- tribute copies to the public, and perform pub- licly and display publicly, by or on behalf of the Government.