21 research outputs found
Resonant Diffraction Radiation from an Ultrarelativistic Particle Moving Close to a Tilted Grating
A simple model for calculating the diffraction radiation characteristics from
an ultrarelativistic charged particle moving close to a tilted ideally
conducting strip is developed. Resonant diffraction radiation (RDR) is treated
as a superposition of the radiation fields for periodically spaced strips. The
RDR characteristics have been calculated as a function of the number of grating
elements, tilted angle, and initial particle energy. An analogy with both the
resonant transition radiation in absorbing medium and the parametric X-ray
radiation is noted.Comment: 17 pages, 12 figures, RevTe
Focusing of transition radiation and diffraction radiation from concave targets
In the article the transition radiation from a relativistic charge crossing a
finite radius paraboloid target with taking into account the pre-wave zone
effect is considered. It is shown that in this case the radiation cone
narrowing occurs in contrast with the transition radiation from the flat target
if the detector is situated at the distance, which is smaller than the focus
distance (the focusing effect) from the target. At the charged particle passage
through the central hole in a paraboloid target the diffraction radiation
focusing (DR) occurs too. The focusing of coherent DR for the non-invasive
measuring of the electron bunch length is proposed.Comment: 11 pages, 10 figures; Talk presented at the RC2005, Frascati, Ital
Resonant Diffraction Radiation and Smith-Purcell Effect
An approach has been developed where the Smith-Purcell radiation (SPR), i.e.
emission of electrons moving close to a periodic structure, is treated as the
resonant diffraction radiation. Simple formulas have been designed for the SPR
intensity for a grating having perfectly conducting strips spaced by a vacuum
gap. The results have been compared with those obtained via other techniques.
It has been shown that the intensity of radiation for the said gratings for a
relativistic case sufficiently exceeds the SPR intensity for the grating made
up by a periodically deformed continuous surface.Comment: 9 pages, LATEX, 3 Postscript figures, uses epsf.sty, submitted to
Phys.Letters
Investigation of resonant polarization radiation of relativistic electrons in gratings at small angles
The Resonant Optical Polarization Radiation (ROPR) in the Smith-Purcell
geometry and the one from the inclined grating at the Tomsk synchrotron and
6-MeV microtron have been investigated. The polarization radiation was observed
at 4.2o from the 200 MeV electron beam and at 5o from the 6.2 MeV electron
beam. Two methods of measurement of ROPR maxima in these two cases have been
used. In the first case (the experiment on synchrotron) we have fixed the
wavelength of radiation using an optical filter; the orientation dependence of
this radiation was measured. In this dependence we have observed two peaks of
radiation from electrons in gold foil grating of 0.1 mm period. The first large
peak is a zeroth order peak in direction of specular reflection, and the second
one is the 1-st order peak of resonant polarization radiation. In the
experiment on microtron the spectra of ROPR from aluminum foil strip grating of
0.2 mm period in the Smith-Purcell geometry were measured, and the peak of the
1-st order Smith-Purcell radiation in these spectra was observed. The
comparison of data obtained with the simulation results has been performed
Generalized surface current method in the macroscopic theory of diffraction radiation
The surface current method known in the theory of electromagnetic waves
diffraction is generalized to be applied for the problems of diffraction
radiation generated by a charged particle moving nearby an ideally-conducting
screen in vacuum. An expression for induced surface current density leading to
the exact results in the theory of transition radiation is derived, and by
using this expression several exact solutions of diffraction radiation problems
are found. Limits of applicability for the earlier known models based on the
surface current conception are indicated. Properties of radiation from a
semi-plane and from a slit in cylinder are investigated at the various
distances to observer.Comment: 8 pages, 8 figure
Experimental study of positron production from a 2.55-mm-thick silicon crystal target using 8-GeV channeling electron beams with high-bunch charges
We have investigated quenching phenomena of channeling radiation through positron production from a silicon crystal hit by a single-bunch electron beam with high-bunch charge at the 8-GeV electron/positron injector linac. The crystal axis, left angle bracket1 1 0right-pointing angle bracket, was aligned to the electron beam with a precise goniometer, and positrons produced in the forward direction with a momentum of 20 MeV/c were detected with a magnetic spectrometer. Positron yields were measured by varying the charge in a bunch with a typical bunch length of not, vert, similar10 ps from 0.1 nC to 2 nC. The corresponding instantaneous current density ranged from 0.15 Ă— 104 to 1.2 Ă— 104 A/cm2. The results show that, at these current densities, the positron yield is proportional to the bunch charge within the experimental accuracy, which implies that no non-linear phenomena are observed in channeling radiation