• F. Zhou, C. Adolphsen, Y.T. Ding, Z. Li, A.E. Vlieks
  SLAC, Menlo Park, California

SLAC is study­ing the fea­si­bil­i­ty of using an X-band RF pho­to­cath­ode gun to pro­duce low emit­tance bunch­es for ap­pli­ca­tions such as an MeV gamma source (in col­lab­o­ra­tion with LLNL) and an in­jec­tor for a com­pact FEL. Sys­tem­at­ic beam dy­nam­ics study are being done for a 5.5 cell X-band gun fol­lowed by sev­er­al 53 cm long high-gra­di­ent X-band ac­cel­er­a­tor struc­tures. A fully 3D pro­gram, Im­pactT*, is used to track par­ti­cles tak­ing into ac­count space charge forces, short-range lon­gi­tu­di­nal and trans­verse wake­fields and the 3D rf fields in the struc­tures, in­clud­ing the quadrupole com­po­nent of the cou­plers. The ef­fect of mis­align­ments of the var­i­ous el­e­ments (drive-laser, gun, solenoid and ac­cel­er­a­tor struc­tures) are being eval­u­at­ed. This paper pre­sents these re­sults and es­ti­mates of the ex­pect­ed bunch emit­tance ver­sus bunch charge and cath­ode gra­di­ent.

*Ji Qiang, LBNL-62326, January 25, 2007.

• F.V. Hartemann, F. Albert, S.G. Anderson, C.P.J. Barty, A.J. Bayramian, T.S. Chu, R.R. Cross, C.A. Ebbers, D.J. Gibson, R.A. Marsh, D.P. McNabb, M. J. Messerly, M. Shverdin, C. Siders
  LLNL, Livermore, California
• E.N. Jongewaard, T.O. Raubenheimer, S.G. Tantawi, A.E. Vlieks
  SLAC, Menlo Park, California
• V. A. Semenov
  UCB, Berkeley, California

Re­cent progress in ac­cel­er­a­tor physics and laser tech­nol­o­gy have en­abled the de­vel­op­ment of a new class of tun­able gam­ma-ray light sources based on Comp­ton scat­ter­ing be­tween a high-bright­ness, rel­a­tivis­tic elec­tron beam and a high in­ten­si­ty laser pulse pro­duced via chirped-pulse am­pli­fi­ca­tion (CPA). A pre­ci­sion, tun­able Mono-En­er­get­ic Gam­ma-ray (MEGa-ray) source driv­en by a com­pact, high-gra­di­ent X-band linac is cur­rent­ly under de­vel­op­ment and con­struc­tion at LLNL. High-bright­ness, rel­a­tivis­tic elec­tron bunch­es pro­duced by an X-band linac de­signed in col­lab­o­ra­tion with SLAC will in­ter­act with a Joule-class, 10 ps, diode-pumped CPA laser pulse to gen­er­ate tun­able γ-rays in the 0.5-2.5 MeV pho­ton en­er­gy range via Comp­ton scat­ter­ing. This MEGa-ray source will be used to ex­cite nu­cle­ar res­o­nance flu­o­res­cence in var­i­ous iso­topes. Ap­pli­ca­tions in­clude home­land se­cu­ri­ty, stock­pile sci­ence and surveil­lance, nu­cle­ar fuel assay, and waste imag­ing and assay. The source de­sign, key pa­ram­e­ters, and cur­rent sta­tus are pre­sent­ed, along with im­por­tant ap­pli­ca­tions, in­clud­ing nu­cle­ar res­o­nance flu­o­res­cence, pho­to-fis­sion, and med­i­cal imag­ing.

• A.E. Vlieks, V.A. Dolgashev, S.G. Tantawi
  SLAC, Menlo Park, California
• S.G. Anderson, F.V. Hartemann, R.A. Marsh
  LLNL, Livermore, California

In sup­port of the T-REX pro­gram at LLNL and the High Gra­di­ent re­search pro­gram at SLAC, a new X-band mul­ti-cell RF gun is being de­vel­oped. This gun, sim­i­lar to an ear­li­er gun de­vel­oped at SLAC for Comp­ton X-ray source pro­gram, will be a stand­ing wave struc­ture made of 5.5 cells op­er­at­ing in the pi mode with cop­per cath­ode. This gun was de­signed fol­low­ing cri­te­ria used to build SLAC X-band high gra­di­ent ac­cel­er­at­ing struc­tures. It is an­tic­i­pat­ed that this gun will op­er­ate with sur­face elec­tric fields on the cath­ode of 200MeV/m with low break­down rate. RF will be cou­pled into the struc­ture through a sym­met­ric final cell with a shape op­ti­mized to elim­inable both dipole and quadru­ple field com­po­nents. In ad­di­tion, ge­om­e­try changes to the orig­i­nal gun, op­er­at­ed with Comp­ton X-ray source, will in­clude a wider RF mode sep­a­ra­tion, re­duced sur­face elec­tric and mag­net­ic fields.

• D.W. Sprehn, A.A. Haase, A. Jensen, E.N. Jongewaard, C.D. Nantista, A.E. Vlieks
  SLAC, Menlo Park, California

A 12 GHz 50MW X-band klystron is under de­vel­op­ment at the SLAC Na­tion­al Ac­cel­er­a­tor Lab­o­ra­to­ry Klystron De­part­ment. The klystron will be fab­ri­cat­ed to sup­port pro­grams cur­rent­ly un­der­way at three Eu­ro­pean Labs; CERN, PSI, and INFN Tri­este. The choice of fre­quen­cy se­lec­tion was due to the CLIC RF fre­quen­cy chang­ing from 30 GHz to the Eu­ro­pean X-band fre­quen­cy of 11.9942 GHz in 2008. Since the Klystron De­part­ment cur­rent­ly builds 50MW klystrons at 11.424 GHz known col­lec­tive­ly as the XL4 klystrons, it was deemed cost-ef­fec­tive to uti­lize many XL4 com­po­nents by leav­ing the gun, elec­tron beam trans­port, solenoid mag­net and col­lec­tor un­changed. To re­al­ize the rf pa­ram­e­ters re­quired, the rf cav­i­ties and rf out­put hard­ware were nec­es­sar­i­ly al­tered. Some im­prove­ments to the rf de­sign have been made to re­duce op­er­at­ing gra­di­ents and in­crease re­li­a­bil­i­ty. Changes in the mul­ti-cell out­put struc­ture, waveg­uide com­po­nents, and the win­dow will be dis­cussed along with test­ing of the de­vices. Five klystrons known as XL5 klystrons are sched­uled for pro­duc­tion over the next two years.

• T.S. Chu, S.G. Anderson, C.P.J. Barty, D.J. Gibson, F.V. Hartemann, R.A. Marsh, C. Siders
  LLNL, Livermore, California
• C. Adolphsen, E.N. Jongewaard, T.O. Raubenheimer, S.G. Tantawi, A.E. Vlieks, J.W. Wang
  SLAC, Menlo Park, California

A Mono-En­er­get­ic Gam­ma-Ray Comp­ton scat­ter­ing light source is being de­vel­oped at LLNL. The elec­tron beam for the in­ter­ac­tion will be gen­er­at­ed by a X-band RF gun and LINAC at the fre­quen­cy of 11.424 GHz. High power RF in ex­cess of 500 MW is need­ed to ac­cel­er­ate the elec­trons to en­er­gy of 250 MeV or greater. Two high power klystrons, each ca­pa­ble of gen­er­at­ing 50 MW, 1.5 msec puls­es, will be the main RF sources for the sys­tem. These klystrons will be pow­ered by state of the art sol­id-state high volt­age mod­u­la­tors. A RF pulse com­pres­sor, sim­i­lar to the SLED II pulse com­pres­sor, will com­press the klystron out­put pulse with a power gain fac­tor of five. For com­pact­ness con­sid­er­a­tion, we are look­ing at a fold­ed RF line. The goal is to ob­tain 500 MW at out­put of the com­pres­sor. The com­pressed pulse will then be dis­tribut­ed to the RF gun and to six trav­el­ing wave ac­cel­er­a­tor sec­tions. Phase shifter and am­pli­tude con­trol are lo­cat­ed at the RF gun input and ad­di­tion­al con­trol points along the LINAC to allow for pa­ram­e­ter con­trol dur­ing op­er­a­tion. This high power RF sys­tem is being de­signed and con­struct­ed. In this paper, we will pre­sent the de­sign, lay­out, and sta­tus of this RF sys­tem.

• R.A. Marsh, S.G. Anderson, C.P.J. Barty, T.S. Chu, C.A. Ebbers, D.J. Gibson, F.V. Hartemann
  LLNL, Livermore, California
• C. Adolphsen, E.N. Jongewaard, T.O. Raubenheimer, S.G. Tantawi, A.E. Vlieks, J.W. Wang
  SLAC, Menlo Park, California

In sup­port of Comp­ton scat­ter­ing gam­ma-ray source ef­forts at LLNL, a mul­ti-bunch test stand is being de­vel­oped to in­ves­ti­gate ac­cel­er­a­tor op­ti­miza­tion for fu­ture up­grades. This test stand will en­able work to ex­plore the sci­ence and tech­nol­o­gy paths re­quired to boost the cur­rent 10 Hz mono-en­er­get­ic gam­ma-ray (MEGa-Ray) tech­nol­o­gy to an ef­fec­tive rep­e­ti­tion rate ex­ceed­ing 1 kHz, po­ten­tial­ly in­creas­ing the av­er­age gam­ma-ray bright­ness by two or­ders of mag­ni­tude. Mul­ti­ple bunch­es must be of ex­ceed­ing­ly high qual­i­ty to pro­duce nar­row-band­width gam­ma-rays. Mod­el­ing ef­forts will be pre­sent­ed, along with plans for a mul­ti-bunch test stand at LLNL. The test stand will con­sist of a 5.5 cell X-band rf pho­toin­jec­tor, sin­gle ac­cel­er­a­tor sec­tion, and beam di­ag­nos­tics. The pho­toin­jec­tor will be a high gra­di­ent stand­ing wave struc­ture, fea­tur­ing a dual feed race­track cou­pler. The ac­cel­er­a­tor will in­crease the elec­tron en­er­gy so that the emit­tance can be mea­sured using quadrupole scan­ning tech­niques. Mul­ti-bunch di­ag­nos­tics will be de­vel­oped so that the beam qual­i­ty can be mea­sured and com­pared with the­o­ry. De­sign will be pre­sent­ed with mod­el­ing sim­u­la­tions, and lay­out plans.

• K.M. Schirm, S. Curt, S. Döbert, G. McMonagle, G. Rossat, I. Syratchev, L. Timeo
  CERN, Geneva
• A.A. Haase, A. Jensen, E.N. Jongewaard, C.D. Nantista, D.W. Sprehn, A.E. Vlieks
  SLAC, Menlo Park, California
• A. Hamdi, F. Peauger
  CEA, Gif-sur-Yvette
• S.V. Kuzikov, A.A. Vikharev
  IAP/RAS, Nizhny Novgorod

The CLIC RF fre­quen­cy has been changed in 2008 from the ini­tial 30 GHz to the Eu­ro­pean X-band 11.9942 GHz per­mit­ting beam in­de­pen­dent power pro­duc­tion using klystrons for CLIC ac­cel­er­at­ing struc­ture test­ing. A de­sign and fab­ri­ca­tion con­tract for five klystrons at that fre­quen­cy has been signed by dif­fer­ent par­ties with SLAC. France (CEA Saclay) is con­tribut­ing a solid state mod­u­la­tor pur­chased in in­dus­try to the CLIC study. RF puls­es over 120 MW peak at 230 ns length will be ob­tained by using a novel SLED I type pulse com­pres­sion scheme de­signed and fab­ri­cat­ed in Nizh­ny Nov­gorod, Rus­sia. The X-band power test stand has been in­stalled in the CLIC Test Fa­cil­i­ty CTF3 for in­de­pen­dent struc­ture and com­po­nent test­ing in a bunker, but al­low­ing, in a later stage, for pow­er­ing RF com­po­nents in the CTF3 beam lines. The de­sign of the fa­cil­i­ty, re­sults from com­mis­sion­ing of the RF power source and the per­for­mance of the Test Fa­cil­i­ty are re­port­ed.