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Register a new userPolarization of Radiation from Planar Channeled Positrons
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The Stokes parameters have been found in the framework of quantum electrodynamics for the description of polarization of radiation emitted by relativistic positrons channeled between (110) planes in Si crystal. The degree of polarization, which is simply given by the contribution of channeling radiation, has been analyzed. Numerical calculation are presented for the frequencies that are most interesting for the sources of polarized high-energy photons.
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A periodically bent Si crystal is shown to efficiently serve for producing highly monochromatic radiation in a gamma-ray energy spectral range. A short-period small-amplitude bending yields narrow undulator-type spectral peaks in radiation from multi-GeV electrons and positrons channeling through the crystal. Benchmark theoretical results on the undulator are obtained by simulations of the channeling with a full atomistic approach to the projectile-crystal interactions over the macroscopic propagation distances. The simulations are facilitated by employing the MBN Explorer package for molecular dynamics calculations on the meso- bio- and nano-scales. The radiation from the ultra-relativistic channeling projectiles is computed within the quasi-classical formalism. The effects due to the quantum recoil are shown to be significantly prominent in the gamma-ray undulator radiation.
Radiation of charged particles passing through a set of equidistant ridges on the surface of a single crystal is calculated. The ridges are rectangular in shape, each of thickness of half of the particle trajectory period at planar channeling in a thick crystal. Positively charged particle entering the first ridge with angle smaller than the critical channeling angle is captured into channeling and changes the direction of its transversal velocity to reversed. Between the half-wave ridges the particle moves along a straight line. Passing through such set of half-wave crystal plates the particle moves on quasi-undulator trajectories. Properties of the particle radiation emitted during their passage through such multicrystal undulator are calculated. The radiation spectrum in each direction is discrete, and the frequency of the first harmonic and the number of harmonics in the spectrum depends on the distance between the plates, on energy of the particles and on the averaged potential energy of atomic planes of the crystal. The radiation is bound to a narrow cone in the direction of the average particle velocity and polarized essentially in a plane orthogonal to the atomic planes of the crystal.
A new scheme to produce very low emittance muon beams using a positron beam of about 45~GeV interacting on electrons on target is presented. One of the innovative topics to be investigated is the behaviour of the positron beam stored in a low emittance ring with a thin target, that is directly inserted in the ring chamber to produce muons. Muons can be immediately collected at the exit of the target and transported to two $mu^+$ and $mu^-$ accumulator rings and then accelerated and injected in muon collider rings. We focus in this paper on the simulation of the e$^+$ beam interacting with the target, the effect of the target on the 6-D phase space and the optimization of the e$^+$ ring design to maximize the energy acceptance. We will investigate the performance of this scheme, ring plus target system, comparing different multi-turn simulations. The source is considered for use in a multi-TeV collider in ref.[1]
A version for intense $gamma $-ray radiation based on the multiphoton scattering of strong laser radiation on relativistic particle beam channeled in a crystal is proposed. The scheme is considered when the incident laser beam and charged paricles beam are counter-propagating and the laser radiation is resonant to the energy levels of transversal motion of channeled particles.
Fast polarization switching of light sources is required over a wide spectral range to investigate the symmetry of matter. In this Letter, we report the first experimental demonstration of the crossed-planar undulator technique at a seeded free-electron laser, which holds great promise for the full control and fast switching of the polarization of short-wavelength radiation. In the experiment, the polarization state of the coherent radiation at the 2nd harmonic of the seed laser is switched successfully. The experiment results confirm the theory, and pave the way for applying the crossed-planar undulator technique for the seeded X-ray free electron lasers.
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