• H. Kotaki, S.V. Bulanov, Y. Hayashi, T. Homma, M. Kando, K. Kawase, J. Koga, M. Mori
  JAEA, Kyoto

Laser wake­field ac­cel­er­a­tion (LWFA) is re­gard­ed as a basis for the next-gen­er­a­tion of charged par­ti­cle ac­cel­er­a­tors. In ex­per­i­ments, it has been demon­strat­ed that LWFA is ca­pa­ble of gen­er­at­ing elec­tron bunch­es with high qual­i­ty: quasi-mo­noen­er­get­ic, low in emit­tance, and a very short du­ra­tion of the order of ten fem­to-sec­onds. Such fem­tosec­ond bunch­es can be used to mea­sure ul­tra­fast phe­nom­e­na. In ap­pli­ca­tions of the laser ac­cel­er­at­ed elec­tron beam, it is nec­es­sary to gen­er­ate a sta­ble elec­tron beam and to con­trol the elec­tron beam. A 40 fs laser pulse with the en­er­gy of 200 mJ is fo­cused onto a su­per­son­ic gas jet. We suc­ceed to gen­er­ate a sta­ble elec­tron beam by using a Ni­tro­gen gas tar­get. The pro­file of the elec­tron beam can be ma­nip­u­lat­ed by ro­tat­ing the laser po­lar­iza­tion. When we use a S-po­lar­ized laser pulse, a 20 MeV elec­tron beam is ob­served with an os­cil­la­tion in the image of the en­er­gy spec­trum. From the os­cil­la­tion, the pulse width of the elec­tron beam is cal­cu­lat­ed to at most a few tens fs. The di­rec­tion of the elec­tron beam can be con­trolled by chang­ing the gas-jet po­si­tion. The self-in­ject­ed elec­tron beam can be con­trolled by the con­trol of the laser and gas jet.

Slides

• M. Mori, S.V. Bulanov, Y. Hayashi, K. Kawase, K. Kondo, A.S. Pirozhkov, A. Sugiyama
  JAEA, Kyoto
• M. Kando
  JAEA APRC, Ibaraki-ken
• H. Kotaki, K. Ogura
  JAEA/Kansai, Kyoto
• H. Nishimura
  ILE Osaka, Suita

The point­ing sta­bil­i­ty and the di­ver­gence of a quasi-mo­noen­er­get­ic elec­tron bunch gen­er­at­ed in a self-in­ject­ed laser-plas­ma ac­cel­er­a­tion regime were in­ves­ti­gat­ed. Gas-jet tar­gets have been ir­ra­di­at­ed with fo­cused 40 fs laser puls­es at the 4-TW peak power. A point­ing sta­bil­i­ty of 2.4 mrad root-mean-square (RMS) and a beam di­ver­gence of 10.6 mrad (RMS) were ob­tained using argon gas-jet tar­get for 50 se­quen­tial shots, while these val­ues were about three times small­er than at the op­ti­mum con­di­tion using he­li­um. In par­tic­u­lar, the peak elec­tron en­er­gy was 9 MeV using argon, which is al­most three times lower than that using he­li­um. This re­sult im­plies that the for­ma­tion of the wake-field is dif­fer­ent be­tween argon and he­li­um, and it plays an im­por­tant role in the gen­er­a­tion of a elec­tron bunch. This sta­bi­liza­tion scheme is avail­able for an­oth­er gas ma­te­ri­al such as ni­tro­gen. At ni­tro­gen gas-jet tar­get, the point­ing sta­bil­i­ty is more im­proved to 1.4 times small­er (1.7 mrad (RMS)) than that in argon gas-jet tar­get and the peak en­er­gy is in­creased to grater than 40 MeV. These re­sults prove that this method not only sta­bi­lize the e-beam but also al­lows con­trol­ling the elec­tron en­er­gy.

• A. Sagisaka, P.R. Bolton, S.V. Bulanov, H. Daido, T. Esirkepov, T. Hori, S. Kanazawa, H. Kiriyama, K. Kondo, S. Kondo, M. Mori, Y. Nakai, M. Nishiuchi, K. Ogura, H. Okada, S. Orimo, A.S. Pirozhkov, H. Sakaki, F. Sasao, H. Sasao, T. Shimomura, A. Sugiyama, H. Sugiyama, M. Tampo, M. Tanoue, D. Wakai, A. Yogo
  JAEA, Kyoto
• I.W. Choi, J. Lee
  APRI-GIST, Gwangju
• H. Nagatomo
  ILE Osaka, Suita
• K. Nemoto, Y. Oishi
  Central Research Institute of Electric Power Industry, Yokosuka-shi, Kanagawa

High-in­ten­si­ty laser and thin-foil in­ter­ac­tions pro­duce high-en­er­gy par­ti­cles, hard x-ray, high-or­der har­mon­ics, and ter­a­hertz ra­di­a­tion. A pro­ton beam driv­en by a high-in­ten­si­ty laser has re­ceived at­ten­tion as a com­pact ion source for med­i­cal ap­pli­ca­tions. We have per­formed the high in­ten­si­ty laser-mat­ter in­ter­ac­tion ex­per­i­ments using a thin-foil tar­get ir­ra­di­at­ed by Ti:sap­phire laser (J-KAREN) at JAEA. In this laser sys­tem, the pulse du­ra­tion is 40 fs (FWHM). The laser beam is fo­cused by an off-ax­is parabol­ic mir­ror at the tar­get. The es­ti­mat­ed peak in­ten­si­ty is ~5x10¹⁹ W/cm². We have de­vel­oped on-line real time mon­i­tors such as a time-of-flight pro­ton spec­trom­e­ter which is placed be­hind the tar­get and in­ter­fer­om­e­ter for elec­tron den­si­ty pro­file mea­sure­ment of pre­formed plas­ma. We ob­served the max­i­mum pro­ton en­er­gy of ~7 MeV.

• M. Nishiuchi, P.R. Bolton, T. Hori, K. Kondo, A.S. Pirozhkov, A. Sagisaka, H. Sakaki, A. Yogo
  JAEA, Ibaraki-ken
• Y. Iseki, T. Yoshiyuki
  Toshiba, Tokyo
• S. Kanazawa, H. Kiriyama, M. Mori, K. Ogura, S. Orimo
  JAEA/Kansai, Kyoto
• A. Noda, H. Souda, H. Tongu
  Kyoto ICR, Uji, Kyoto
• T. Shirai
  NIRS, Chiba-shi

The in­ter­ac­tion be­tween the high in­ten­si­ty laser and the solid tar­get pro­duces a strong elec­tro­stat­ic pro­ton ac­cel­er­a­tion field (1 TV/m) with ex­traor­di­nary small size, con­tribut­ing to down­siz­ing of the par­ti­cle ac­cel­er­a­tor. The pro­ton beam ex­hibits sig­nif­i­cant fea­tures. hav­ing very small source size(~10 um), short pulse du­ra­tion (~ps) and very low trans­verse emit­tance. How­ev­er it is a di­verg­ing beam (half angle of ~10 deg) with wide en­er­gy spread of ~100 %. Be­cause of these pe­cu­liar char­ac­ter­is­tics the pro­ton beam at­tracts many fields for ap­pli­ca­tions in­clud­ing med­i­cal ap­pli­ca­tions. To pre­serve these pe­cu­liar char­ac­ter­is­tics, which are not pos­sessed by those beams from the con­ven­tion­al ac­cel­er­a­tors, to­wards the ir­ra­di­a­tion points, we need to es­tab­lish a pe­cu­liar beam trans­port line. As the first step, here we re­port the demon­stra­tion of the pro­to-type laser-driv­en pro­ton med­i­cal ac­cel­er­a­tor beam line in which we com­bine the laser-driv­en pro­ton source with the beam trans­port tech­nique al­ready es­tab­lished in the con­ven­tion­al ac­cel­er­a­tor for the pur­pose of com­par­i­son be­tween the data and the par­ti­cle trans­port sim­u­la­tion code, PARMI­LA*.

*Harunori Takeda, 2005, Parmila LANL (LA-UR-98-4478).