JAEA, Kyoto
Parametric X-ray generation is one of the ways to obtain a monochromatic X-ray. The X-ray is generated through the interaction between high energy electrons and a crystal. The relationship between an X-ray wavelength and an angle of emission is followed by the Bragg condition. Therefore the monochromatic energy of the X-ray can be varied continuously by rotating the crystal. This tunability of X-ray wavelength is suitable for various applications. Usually a single photon counting method is utilized for measuring of the parametric X-rays. Although this method has an advantage to obtain clear energy spectrum, it takes long time. Here, we have measured 10 keV parametric X-rays with applying a rocking curve method. In this scheme, a large number of parametric X-rays are detected simultaneously. This enables us to find and tune the parametric X-ray quickly. As a result, we could find the sharp peak from this method with the Microtron accelerator (150MeV, 20 - 30 pC) at JAEA and a Si crystal. Since the peak angle is consistent to the Bragg condition for the 10 keV parametric X-ray generation, we think 10 keV photons have been generated through the parametric X-ray mechanism.
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/Kansai, Kyoto
Intense laser pulse is utilized to generate compact sources of electrons, ions, x-rays, neutrons. Recently, high energy negative ions are also observed in experiments using cluster or gas target*. To explain the acceleration of negative ions from laser-generated plasmas, we proposed Coulomb implosion mechanism**. When clusters or underdense plasmas are irradiated by an intense laser pulse, positive ions are accelerated inside the clusters or in the self-focusing channel by the Coulomb explosion. This could lead to the acceleration of negative ions towards target center. The maximum energy of negative ions is typically several times lower than that of positive ions. A theoretical description and corresponding Particle-in-Cell simulations of Coulomb implosion mechanism are presented. We show the evidence of the negative ion acceleration observed in our experiments using high intensity laser pulse and the cluster-gas targets.
* S.Ter-Avetisyan et al., J. Phys. B 37 (2004) 3633.
** T.Nakamura et al., Phys. Plasmas 16 (2009) 113106.
WERC, Tsuruga , Fukui
We have operated the accelerator system which consists of a tandem accelerator and a synchrotron since the completion of the construction and beam commissioning at the Wakasa-wan Energy Research Center, Tsuruga, Japan in 2000. The acceleration voltage of the tandem accelerator amounts to 5 MV and is generated by the Dynamitron-type cascade voltage doubler rectifier. The beam from the tandem accelerator is transported to the MeV-ion experimental area for the irradiation to the industrial or biological material and for the ion beam analysis. The tandem beam is also injected to the 200 MeV proton synchrotron. The synchrotron beam has been used for the high energy irradiation and the cancer therapy. The tandem accelerator is used for a lot of purposes including cancer therapy, therefore, stable operation of the system and efficient sharing of the operation duration are required. Developments of the accelerator are presented putting a stress on the stable and efficient operation of the system in this paper.