• M. Migliorati
  Rome University La Sapienza, Roma
• M. Ferrario, C. Vaccarezza
  INFN/LNF, Frascati (Roma)
• C. Ronsivalle
  ENEA C.R. Frascati, Frascati (Roma)
• M. Venturini
  LBNL, Berkeley, California

Ve­loc­i­ty bunch­ing (or RF com­pres­sion) rep­re­sents a promis­ing tech­nique com­ple­men­tary to mag­net­ic com­pres­sion to achieve the high peak cur­rent re­quired in the linac drivers for FELs. Here we re­port on re­cent progress aimed at char­ac­ter­iz­ing the RF com­pres­sion from the point of view of the mi­crobunch­ing in­sta­bil­i­ty. We em­pha­size the de­vel­op­ment of a lin­ear the­o­ry for the gain func­tion of the in­sta­bil­i­ty and its val­i­da­tion against macropar­ti­cle sim­u­la­tions that rep­re­sents a use­ful tool in the eval­u­a­tion of the com­pres­sion schemes for FEL sources.

• C. Vaccarezza, E. Chiadroni, M. Ferrario
  INFN/LNF, Frascati (Roma)
• G. Dattoli, L. Giannessi, M. Quattromini, C. Ronsivalle
  ENEA C.R. Frascati, Frascati (Roma)
• M. Migliorati
  Rome University La Sapienza, Roma
• M. Venturini
  LBNL, Berkeley, California

The ef­fects of mi­crobunch­ing in­sta­bil­i­ty for the SPARX ac­cel­er­a­tor have been an­a­lyzed by means of dif­fer­ent nu­mer­i­cal sim­u­la­tion codes and an­a­lyt­i­cal ap­proach. The laser heater coun­ter­act­ing ac­tion has been also ad­dressed in order to op­ti­mize the pa­ram­e­ters of the com­pres­sion sys­tem, ei­ther hy­brid RF plus mag­net­ic chi­cane or only mag­net­ic, and pos­si­bly en­hance the FEL per­for­mance.

• G. Gatti, M. Bellaveglia, E. Chiadroni, L. Cultrera, M. Ferrario, D. Filippetto, C. Vicario
  INFN/LNF, Frascati (Roma)
• A. Bacci, A.R. Rossi
  Istituto Nazionale di Fisica Nucleare, Milano
• P. Musumeci
  UCLA, Los Angeles
• H. Tomizawa
  JASRI/SPring-8, Hyogo-ken

Shin­ing a pho­to­cath­ode at the same time with an UV laser able to ex­tract elec­trons and an IR laser prop­er­ly tuned could in­flu­ence the way the elec­tron beam is gen­er­at­ed. Such a pro­cess is under in­ves­ti­ga­tion at SPARC, through di­rect mea­sure­ments, as much as through com­put­er codes as­sess­ment stud­ies.

• M. Ferrario, D. Alesini, F. A. Anelli, M. Bellaveglia, M. Boscolo, L. Cacciotti, M. Castellano, E. Chiadroni, L. Cultrera, G. Di Pirro, L. Ficcadenti, D. Filippetto, S. Fioravanti, A. Gallo, G. Gatti, A. Mostacci, E. Pace, R.S. Sorchetti, C. Vaccarezza
  INFN/LNF, Frascati (Roma)
• A. Bacci, V. Petrillo, A.R. Rossi, L. Serafini
  Istituto Nazionale di Fisica Nucleare, Milano
• A. Cianchi, B. Marchetti
  INFN-Roma II, Roma
• L. Giannessi, A. Petralia, C. Ronsivalle
  ENEA C.R. Frascati, Frascati (Roma)
• O. Limaj
  University of Rome La Sapienza, Rome
• M. Moreno, M. Serluca
  INFN-Roma, Roma
• J.B. Rosenzweig
  UCLA, Los Angeles, California
• H. Tomizawa
  JASRI/SPring-8, Hyogo-ken
• C. Vicario
  PSI, Villigen

The pri­ma­ry goal of the SPARC pro­ject is the com­mis­sion­ing of the SASE FEL op­er­at­ing at 500 nm driv­en by a 150-200 MeV high bright­ness pho­toin­jec­tor. Ad­di­tion­al ex­per­i­ments are fore­seen also in the HHG Seed­ed con­fig­u­ra­tion at 266, 160 and 114 nm. A sec­ond beam line host­ing a THz source has been re­cent­ly com­mis­sioned. The re­cent suc­cess­ful op­er­a­tion of the SPARC in­jec­tor in the Ve­loc­i­ty Bunch­ing (VB) mode has opened new per­spec­tives to con­duct ad­vanced beam dy­nam­ics ex­per­i­ments with ul­tra-short elec­tron puls­es able to ex­tend the THz spec­trum and to drive the FEL in the SASE Sin­gle Spike mode. More­over a new tech­nique called Laser Comb, able to gen­er­ate a train of short puls­es with high rep­e­ti­tion rate, as the one re­quired to drive co­her­ent plas­ma wake field ex­ci­ta­tion, has been test­ed in the VB con­fig­u­ra­tion. The en­er­gy/den­si­ty mod­u­la­tion pro­duced by an in­frared laser pulse in­ter­act­ing with the elec­tron beam near the cath­ode has been also in­ves­ti­gat­ed. In this paper we re­port the ex­per­i­men­tal re­sults ob­tained so far and the com­par­i­son with sim­u­la­tions.

• E. Chiadroni, F. A. Anelli, M. Bellaveglia, M. Boscolo, M. Castellano, L. Cultrera, G. Di Pirro, M. Ferrario, L. Ficcadenti, D. Filippetto, S. Fioravanti, G. Gatti, E. Pace, R.S. Sorchetti, C. Vaccarezza
  INFN/LNF, Frascati (Roma)
• A. Bacci, A.R. Rossi
  Istituto Nazionale di Fisica Nucleare, Milano
• P. Calvani, S. Lupi, D. Nicoletti
  Università di Roma I La Sapienza, Roma
• L. Catani, B. Marchetti
  INFN-Roma II, Roma
• A. Cianchi
  Università di Roma II Tor Vergata, Roma
• O. Limaj
  University of Rome La Sapienza, Rome
• A. Mostacci
  Rome University La Sapienza, Roma
• C. Ronsivalle
  ENEA C.R. Frascati, Frascati (Roma)

The re­gion of the spec­trum from 0.3 to 5 THz is of great in­ter­est for sev­er­al ex­per­i­ments in dif­fer­ent areas of re­search. A THz ra­di­a­tion source can be pro­duced at SPARC as co­her­ent tran­si­tion ra­di­a­tion emit­ted by ei­ther a com­pressed or lon­gi­tu­di­nal­ly mod­u­lat­ed beam in­ter­cept­ing a metal foil placed at 45° with re­spect to the beam prop­a­ga­tion. Re­sults on the char­ac­ter­i­za­tion of the THz source at SPARC are de­scribed in the paper.

Slides

• R. Boni, D. Alesini, M. Bellaveglia, G. Di Pirro, M. Ferrario, L. Ficcadenti, A. Gallo, F. Marcellini, E. Pace, B. Spataro, C. Vaccarezza
  INFN/LNF, Frascati (Roma)
• A. Bacci
  Istituto Nazionale di Fisica Nucleare, Milano
• A. Mostacci, L. Palumbo, V. Spizzo
  Rome University La Sapienza, Roma
• C. Ronsivalle
  ENEA C.R. Frascati, Frascati (Roma)

In the frame of the SPARC-X pro­ject, the en­er­gy of the Pho­to-In­jec­tor SPARC, in op­er­a­tion at INFN-LNF, will be up­grad­ed from 180 to 250 MeV by re­plac­ing a low gra­di­ent S-band trav­el­ing wave ac­cel­er­at­ing sec­tion with two C-band units, de­signed and de­vel­oped at LNF. The new sys­tem will con­sist of a 50 MW klystron, sup­plied by a pulsed mod­u­la­tor, to feed the high gra­di­ent C-band struc­tures through a RF pulse com­pres­sor. This paper deals with the de­sign of the full sys­tem, the C-band R&D ac­tiv­i­ty and study of the re­lat­ed beam dy­nam­ics.

• J.B. Rosenzweig, G. Andonian, A. Fukasawa, E. Hemsing, G. Marcus, A. Marinelli, P. Musumeci, B.D. O'Shea, F.H. O'Shea, C. Pellegrini, D. Schiller, G. Travish
  UCLA, Los Angeles, California
• P.H. Bucksbaum, M.J. Hogan, P. Krejcik
  SLAC, Menlo Park, California
• M. Ferrario
  INFN/LNF, Frascati (Roma)
• S.J. Full
  Penn State University, University Park, Pennsylvania
• P. Muggli
  USC, Los Angeles, California

Re­cent ini­tia­tives at UCLA con­cern­ing ul­tra-short, GeV elec­tron beam gen­er­a­tion have been aimed at achiev­ing sub-fs puls­es ca­pa­ble of driv­ing X-ray free-elec­tron lasers (FELs) in sin­gle-spike mode. This uses of very low charge beams, which may allow ex­ist­ing FEL in­jec­tors to pro­duce few-100 at­tosec­ond puls­es, with very high bright­ness. To­wards this end, re­cent ex­per­i­ments at the Stan­ford X-ray FEL (LCLS, first of its kind, built with es­sen­tial UCLA lead­er­ship) have pro­duced ~2 fs, 20 pC elec­tron puls­es. We dis­cuss here ex­ten­sions of this work, in which we seek to ex­ploit the beam bright­ness in FELs, in tan­dem with new de­vel­op­ments at UCLA in cryo­genic un­du­la­tor tech­nol­o­gy, to cre­ate com­pact ac­cel­er­a­tor/un­du­la­tor sys­tems that can lase below 0.15 Angstroms, or be used to per­mit 1.5 Angstrom op­er­a­tion at 4.5 GeV. In ad­di­tion, we are now de­vel­op­ing ex­per­i­ments which use the pre­sent LCLS fs puls­es to ex­cite plas­ma wake­fields ex­ceed­ing 1 TV/m, per­mit­ting a table-top TeV ac­cel­er­a­tor for fron­tier high en­er­gy physics ap­pli­ca­tions.