• S. Kashiwagi, K. Furuhashi, G. Isoyama, R. Kato, M. Morio, N. Sugimoto, Y. Terasawa
  ISIR, Osaka
• H. Hayano, H. Sugiyama, T. Takatomi, J. Urakawa
  KEK, Ibaraki
• H. Iijima, M. Kuriki
  HU/AdSM, Higashi-Hiroshima

We con­duct re­search on Free Elec­tron Laser (FEL) in the in­frared re­gion and pulse ra­di­ol­y­sis for ra­di­a­tion chem­istry using the 40 MeV, 1.3 GHz L-band linac of Osaka Uni­ver­si­ty. At pre­sent, the L-band linac is equipped with a thermion­ic elec­tron gun. It can ac­cel­er­ate a high-in­ten­si­ty sin­gle-bunch beam with charge up to 91 nC but the nor­mal­ized emit­tance is large. In order to ad­vance the re­search, we have begun de­vel­op­ment of a pho­to­cath­ode RF gun for the L-band elec­tron linac in col­lab­o­ra­tion with KEK and Hi­roshi­ma Uni­ver­si­ty. We start the basic de­sign of the RF gun cav­i­ty for the L-band linac at ISIR, Osaka Uni­ver­si­ty, based on the 1.5 cells, which is a nor­mal con­duct­ing pho­to­cath­ode RF gun. A ma­te­ri­al of the cath­ode should be Cs2Te, which has the high quan­tum ef­fi­cien­cy of a few per­cents, to pro­duce a beam with high charge up to 30 nC/bunch. We im­prove the cool­ing sys­tem of the cav­i­ty for high duty op­er­a­tion to sup­press the ther­mal de­for­ma­tion due to the heat load of input rf power. The sim­u­la­tion study has been also per­formed for the L-band linac at ISIR with a high charge elec­tron beam. In this con­fer­ence, we de­scribe the de­tails of the L-band pho­to­cath­ode RF gun de­vel­op­ment.

• R. Kato, K. Furuhashi, G. Isoyama, S. Kashiwagi, M. Morio, S. Suemine, N. Sugimoto, Y. Terasawa
  ISIR, Osaka
• K. Tsuchiya, S. Yamamoto
  KEK, Ibaraki

We have been de­vel­op­ing a Ter­a­hertz free elec­tron laser (FEL) based on the 40 MeV, 1.3 GHz L-band elec­tron linac at the In­sti­tute of Sci­en­tif­ic and In­dus­tri­al Re­search (ISIR), Osaka Uni­ver­si­ty. After the FEL las­ing at the wave­length of 70 um (4.3 THz)*, next tar­gets of the FEL de­vel­op­ment are to ex­tend the avail­able laser wave­length, to in­crease the FEL power, and to eval­u­ate char­ac­ter­is­tics of FEL. Since the low­est en­er­gy of the linac was re­strict­ed by a fixed-ra­tio power di­vider be­tween the ac­cel­er­a­tion tube and the bunch­er, we have pre­pared the new one with a dif­fer­ent ratio to ex­tend the wave­length longer side. As a re­sult, the wave­length re­gion is able to be ex­tend­ed to 25 - 147 um (12.5 - 2 THz). The max­i­mum out­put en­er­gy of the FEL macropulse so far ob­tained is 3.6 mJ at 66 um. The peak macropulse power avail­able to user ex­per­i­ments is es­ti­mat­ed to be 1 kW or less, given that the pulse du­ra­tion is 3 us. Three users groups have begun ex­per­i­ments using the FEL. We will re­port these re­cent ac­tiv­i­ties on the Ter­a­hertz FEL.

* G. Isoyama, R. Kato, S. Kashiwagi, T. Igo, Y. Morio, Infrared Physics & Technology 51 (2008) 371-374.

• S. Kashiwagi, G. Isoyama, R. Kato
  ISIR, Osaka
• K. Tsuchiya, S. Yamamoto
  KEK, Ibaraki

The edge-fo­cus­ing (EF) wig­gler has been fab­ri­cat­ed to eval­u­ate its per­for­mance rig­or­ous­ly with the mag­net­ic field mea­sure­ment. It is a 5-pe­ri­od pla­nar wig­gler with an edge angle of 2° and a pe­ri­od length of 60 mm. The mag­net­ic field is mea­sured using Hall probes at four dif­fer­ent wig­gler gaps. It is ex­per­i­men­tal­ly con­firmed that a high field gra­di­ent of 1.0 T/m is re­al­ized, as de­signed, along the beam axis. The mag­net­ic field gra­di­ent of the EF wig­gler is de­rived as a func­tion of the mag­net­ic gap. The field gra­di­ent de­creas­es with in­creas­ing mag­net gap more slow­ly than the peak mag­net­ic field does for the pre­sent ex­per­i­men­tal model. An an­a­lyt­ic for­mu­la for the field gra­di­ent of the EF wig­gler is de­rived and it is shown that the slope of the field gra­di­ent with the mag­net gap can be changed by vary­ing the mag­net width of the EF wig­gler. We an­a­lyzed the re­la­tion be­tween the ori­en­ta­tion er­rors of the mea­sure­ment sys­tem and the mea­sured mag­net­ic field or field gra­di­ent using a model mag­net­ic field of the EF wig­gle. We cor­rect­ed the mea­sure­ment mag­net­ic field based on this anal­y­sis and eval­u­at­ed the per­for­mance of the EF wig­gler.

• G. Isoyama, M. Fujimoto, K. Furuhashi, S. Kashiwagi, R. Kato, M. Morio, J. Shen, S. Suemine, N. Sugimoto, Y. Terasawa
  ISIR, Osaka
• S. Hirata
  Hiroshima University, Faculty of Science, Higashi-Hirosima

The 40 MeV L-band elec­tron linac at the In­sti­tute of Sci­en­tif­ic and In­dus­tri­al Re­search, Osaka Uni­ver­si­ty is ex­ten­sive­ly used for var­i­ous ap­pli­ca­tions on ad­vanced beam sci­ences in­clud­ing ra­di­a­tion chem­istry by means of pulse ra­di­ol­y­sis and de­vel­op­ment of the free elec­tron laser in the THz re­gion. It was con­struct­ed in 1975-78 and has been re­mod­eled some­times for im­prov­ing its per­for­mance. The most re­cent one was made in 2002-2004 for high­er op­er­a­tional sta­bil­i­ty and re­pro­ducibil­i­ty, re­sult­ing in sig­nif­i­cant ad­vances in the stud­ies. We will re­port the pre­sent sta­tus of the linac and re­sults of its per­for­mance eval­u­a­tion.

• M. Kuriki, H. Iijima
  HU/AdSM, Higashi-Hiroshima
• H. Hayano, Y. Honda, H. Sugiyama, J. Urakawa
  KEK, Ibaraki
• G. Isoyama, S. Kashiwagi, R. Kato
  ISIR, Osaka
• E. Katin, E. Khazanov, V. Lozhkarev, G. Luchinin, A. Poteomkin
  IAP/RAS, Nizhny Novgorod
• G. Shirkov, G.V. Trubnikov
  JINR, Dubna, Moscow Region

Aim of Su­per-con­duct­ing Test Fa­cil­i­ty (STF) at KEK is demon­strat­ing tech­nolo­gies for In­ter­na­tion­al Lin­ear Col­lid­er. In STF, one full RF unit will be de­vel­oped and beam ac­cel­er­a­tion test will be made. In su­per-con­duct­ing ac­cel­er­a­tor, pre­cise RF con­trol in phase and power is es­sen­tial be­cause the input RF power should be bal­anced to beam ac­cel­er­at­ing power. To demon­strate the sys­tem fea­si­bil­i­ty, the beam ac­cel­er­at­ing test is an im­por­tant step in R&D phase of STF and ILC. To pro­vide ILC for­mat beam for STF, we de­vel­op an elec­tron source based on pho­to-cath­ode L-band RF gun. To gen­er­ate ILC for­mat beam, we de­vel­oped a laser sys­tem based on Yb fiber os­cil­la­tor in 40.6 MHz. The pulse rep­e­ti­tion is de­creased by pick­ing puls­es in 2.7 MHz, which meets ILC bunch spac­ing, 364 ns. The pulse is then am­pli­fied by YLF laser up to 8 uJ per pulse in 1 mm. The light is con­vert­ed to 266 nm by SHG and FHG. Fi­nal­ly, 1.5 uJ per pulse is ob­tained and 3.2 nC bunch charge will be made. We re­port the basic per­for­mance of the laser sys­tem from the ac­cel­er­a­tor tech­nol­o­gy point of a view.