Y. Takabayashi

Quantum effects for parametric X-ray radiation during channeling: Theory and first experimental observation

The theory of X-ray radiation from relativistic channeled electrons at the Bragg angles—parametric X-ray radiation (PXR) during channeling (PXRC)—is developed while accounting for two quantum effects: the initial population of bound states of transverse motion and the transverse “form-factor” of channeled electrons. An experiment was conducted using a 255 MeV electron beam from a linac at the SAGA Light Source. We have identified a difference in the angular distributions of PXR and PXRC and obtained a fairly good agreement between the theoretical and experimental results.

Peculiarities of Angular Distribution of Electrons at Si Channeling

The properties of both angular and spatial distribution of 255 MeV electrons at channeling in silicon crystal has been investigated experimentally at the linac injector of SAGA light source and by computer simulations. The simulation of trajectories, angular and spatial distributions of electrons on the screen monitor has been performed taking into account initial spatial as well as angular beam divergence of electron beam. Both experimental data and simulations show the brilliant effect of so-called doughnut scattering.

The SAGA Light Source

Saga prefectural government operates a synchrotron light facility mainly for industrial applications of the synchrotron light. The facility comprises a 1.4 GeV storage ring, a 250 MeV linac as an electron injector and beamlines. The lattice of the storage ring is designed to perform as small emittance as 25 nm‐radian and has long straight sections of 2.9 m length for installing insertion devices. Three beam lines have been prepared by Saga prefectural government and one by Saga University.

Planar channelling of relativistic electrons in half-wave silicon crystal and corresponding radiation

Half-wavelength crystal (HWC) is a thin crystal, when a channeled particle experiences only one collision with crystallographic plane during its motion through a HWC crystal. Recently, the authors of Ref. [1] experimentally demonstrated that planar channeled 2 MeV protons were successfully mirrored by a thin silicon HWC. In continuation of this work, the mirroring effect was observed at very high energy at CERN-SPS [2]. In Ref. [3] we performed the detailed experimental investigations and computer simulations of channeling of 255 MeV electrons in the 1 μm thickness silicon HWC. Here, we present new experimental data on planar and axial channeling of 255 MeV electrons in a 0.7 μm Si HWC resently obtained at SAGA LS Facility and comparison with computer simulations. The angular distribution of electrons after penetration through the HWC crystal revealed the number of peculiarities. Also we present calculated radiation spectra from electrons channeled in HWC and compare that with radiation spectra of electrons moving in an arc [4] (never studied experimentally).

Parametric Channeling Radiation and its Application to the Measurement of Electron Beam Energy

We have proposed a method for observing parametric channeling radiation (PCR) and of applying it to the measurement of electron beam energy. The PCR process occurs if the energy of the channeling radiation coincides with the energy of the parametric X‐ray radiation (PXR). The PCR process can be regarded as the diffraction of “virtual channeling radiation”. We developed a scheme for beam energy measurement and designed an experimental setup. We also estimated the beam parameters, and calculated the angular distributions of PXR and PCR. These considerations indicate that the observation of PCR is promising.