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.
JAEA, Kyoto
JAEA APRC, Ibaraki-ken
JAEA/Kansai, Kyoto
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.
JAEA, Kyoto
APRI-GIST, Gwangju
ILE Osaka, Suita
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.
JAEA, Ibaraki-ken
Toshiba, Tokyo
JAEA/Kansai, Kyoto
Kyoto ICR, Uji, Kyoto
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).