Development of Yb-Based Laser System for Crab Crossing Laser-Compton Scattering

We are going to demonstrate the principle of crab crossing in laser-Compton scattering which creates head-on collision in a pseudo manner to enhance the intensity of laserCompton X-ray. When the electron beam is tilted by half of the collision angle, the scattered X-rays becomes the largest. Calculation shows that more than threefold luminosity will be achieved in our system and could be larger luminosity depending on the beam parameters. The intensity of scattered light can be efficiently enhanced by using a collision laser with high intensity, high quality and ultrashort pulse duration. Thus, we have introduced a regenerative amplifier using ceramics thin-disk as a collision laser and developed a dedicated laser system. In this conference, we will report on our laser system and results of crab crossing laser-Compton scattering. INTRODUCTION Laser-Compton scattering (LCS) is a phenomenon in which the energy of an electron is transferred to a laser photon and a high energy photon beam can be generated. The experiment using the 6GeV electron storage ring and ruby laser in 1965 is the beginning of the LCS experiment [1], and since then, the development of the LCS technology is progressing with that of the electron accelerator and the laser technology. In the present circumstances, an X-ray tube is used for X-ray imaging and non-destructive inspection, but the wide energy width causes a reduction in resolution and contrast of X-ray images. There are large synchrotron radiation facilities (ex: SPring-8) as an X-ray source with high brightness and high stability, but the facility is huge and not suitable for industrial applications. On the other hand, laser-Compton X-ray is quasi-monochromatic, high brightness, excellent in directivity and short pulse characteristics. In LCS X-ray source, since the energy of the electron beam is lower by about two orders, the accelerator facility can be miniaturized. LCS is expected for industrial application as a compact X-ray source, but for that purpose it is necessary to enhance intensity of X-ray. In this paper, we report on laser system development for increasing the scattered Xray and collision experiment. LCS AND CRAB CROSSING Laser-Compton Scattering Figure 1: Schematic of LCS. The maximum X-ray energy (�� ��) would be obtained along the electron beam axis � = and written as �� �� ≃ 2�0 + cos� (1) Here, is � � ⁄ , where c and v the velocities of light and electrons, respectively. The energy of the scattered light is variable by adjusting the beam energy and the collision angle of the laser. Further, the polarization of the scattered Xray follows the polarization characteristics of the collision laser and exhibits high polarization. In the case of collisions between pulses, the scattered X-ray also becomes pulses and exhibits short pulse characteristics. The number of scattered photons is given by the product of cross section and luminosity, as follows. � = � × � (2) Since the total cross section is unchangeable once the laser wavelength and beam energy is decided, it is necessary to increase the luminosity as much as possible to obtain the high brightness X-ray. Luminosity can be expressed as seen in Eq. (3). �� is the number of electrons in a bunch and � is the number of photons in a laser pulse. Assuming that the electron beam and the laser are Gaussian, ��, �� , �� represents the sizes of the horizontal, vertical, and longitudinal respectively. The subscripts e is for the electron beam and l is for the laser. Table 1 shows the expected experimental parameters assumed for the system. Table 1: Parameters of Electron Beam and Laser Pulse Electron Beam Laser Pulse Energy 4.2 MeV 1.2 eV(1030nm) Intensity 40 pC 10 mJ Transverse Size 100 μm 50 μm Duration 3 ps(rms) 1 ps(FWHM) The relationships between the collision angle and the luminosity are shown in Figure 2. Figure 1 shows the collisional scattering (LCS) of the electron beam (Lorentz factor γ) and the laser (energy of laser photon 0). ____________________________________________ † ryosuke-0706@asagi.waseda.jp 10th Int. Particle Accelerator Conf. IPAC2019, Melbourne, Australia JACoW Publishing ISBN: 978-3-95450-208-0 doi:10.18429/JACoW-IPAC2019-THPGW035 MC2: Photon Sources and Electron Accelerators T25 Lasers THPGW035 3657 Co nt en tf ro m th is w or k m ay be us ed un de rt he te rm so ft he CC BY 3. 0 lic en ce (© 20 19 ). A ny di str ib ut io n of th is w or k m us tm ai nt ai n at tri bu tio n to th e au th or (s ), tit le of th e w or k, pu bl ish er ,a nd D O I