25 research outputs found
Diffraction Radiation Diagnostics for Moderate to High Energy Charged Particle Beams
Diffraction radiation (DR) is produced when a charged particle passes through
an aperture or near a discontinuity in the media in which it is traveling. DR
is closely related to transition radiation (TR), which is produced when a
charged particle traverses the boundary between media with different dielectric
constants. In contrast to TR, which is now extensively used for beam diagnostic
purposes, the potential of DR as a non-interceptive, multi-parameter beam
diagnostic remains largely undeveloped. For diagnostic measurements it is
useful to observe backward reflected DR from an circular aperture or slit
inclined with respect to the beam velocity. However, up to now, well founded
equations for the spectral-angular intensities of backward DR from such
apertures have not been available. We present a new derivation of the spectral
angular intensity of backward DR produced from an inclined slit for two
orientations of the slit axis, i.e. perpendicular and parallel to the plane of
incidence. Our mathematical approach is generally applicable to any geometry
and simpler than the Wiener Hofp method previously used to calculate DR from
single knife edges. Our results for the slit are applied to the measurement of
orthogonal beam size and divergence components. We discuss the problem of
separating the simultaneous effects of these beam parameters on the angular
distribution of DR and provide solutions to this difficulty. These incude using
the horizontal and vertical polarization components of the radiation from a
single slit and interferences from two inclined slits. Examples of DR
diagnostics for a 500 MeV beam are presented and the current limitations to the
technique are discussed.Comment: 32 pages,including 14 figures; submitted to NIM
Recommended from our members
Initial Search for 9-keV XTR from a 28-GeV Beam at SPPS
The potential to use x-ray transition radiation (XTR) as a beam diagnostic and coherent XTR (CXTR) as a gain diagnostic in an x-ray FEL was proposed previously. At that time we noted that the unique configuration of the SLAC Sub-picosecond Photon Source (SPPS) with its known x-ray wiggler source, a special three-element x-ray monochromator, x-ray transport line, and experimental end station with x-ray detectors made it an ideal location for an XTR feasibility experiment. Estimates of the XTR compared to the SPPS source strength were done, and initial experiments were performed in September 2005. Complementary measurements on optical transition radiation (OTR) far-field images from a 7-GeV beam are also discussed
Higher order parametric X-ray spectra in mosaic graphite and single silicon crystals
We have observed up to eight orders (n) in the spectra of parametric x-radiation, in the range 5-40
keV, produced by the interaction of a 90 Mev electron beam with mosaic graphite and 90 and 35 Mev beams with single silicon crystals. The measured yields and intensity ratios, I(2)/I(n= I), in graphite
are not in agreement with the theory of PXR for mosaic crystals. In comparison, the yield and
ratios of intensities in silicon are close to the predictions of PXR theory for perfect crystals.
The bandwidths of spectral lines measured in both silicon and graphite are in good agreement with
theoretical predictions, and are determined by the angular field of view of the detector.U.S. Department of EnergyDNANaval Postgraduate SchoolContract No. DE-FG03-91ER8109
Production of x-rays by the interaction of charged particle beams with periodic structures and crystalline materials
We describe our recent experimental study of the production of x-rays by an electron beam interacting with a crystal lattice, i.e. parametric x-ray (PX) generation. In this radiation process the virtual photon field associated with a relativistic electron traveling in a crystal is diffracted by the crystal lattice in the same way that real x-rays are diffracted by crystals. The radiation produced satisfies the Bragg condition associated with the diffraction of the virtual photons which are nearly parallel to the velocity of the electrons. This phenomenon is associated with a more general class of radiation production
mechanisms which include transition radiation (TR), diffraction radiation (DR), and Smith-Purcell radiation. In each case, radiation is produced when the particle's fields are altered by interacting with a
material whose dielectric constant varies along or near the particle's trajectory. The usual acceleration mechanism for the production of radiation is not involved in these phenomena. In the case of a crystal,
the periodic electric susceptibility interacting with the particle's field produces parametric x-rays. We will also present a theoretical overview of this phenomenon which can be used to generate monochromatic,
linearly polarized, directional x-rays. Accelerators with energies ranging from a few MeV to hundreds of MeV may be used as drivers for novel parametric x-ray generators for various applications requiring the unique properties of these sources
Recommended from our members
A concept for Z-dependent microbunching measurements with coherent X-ray transition radiation in a sase FEL
We present an adaptation of the measurements performed in the visible-to-VUV regime of the z-dependent microbunching in a self-amplified spontaneous emission (SASE) free-electron laser (FEL). In these experiments a thin metal foil was used to block the more intense SASE radiation and to generate coherent optical transition radiation (COTR) as one source in a two-foil interferometer. However, for the proposed x-ray SASE FELs, the intense SASE emission is either too strongly transmitted at 1.5 Angstrom or the needed foil thickness for blocking scatters the electron beam too much. Since x-ray transition radiation (XTR) is emitted in an annulus with opening angle 1/g = 36 mrad for 14.09-GeV electrons, we propose using a thin foil or foil stack to generate the XTR and coherent XTR (CXTR) and an annular crystal to wavelength sort the radiation. The combined selectivity in angle and wavelength will favor the CXTR over SASE by about eight orders of magnitude. Time-dependent GINGER simulations support the z-dependent gain evaluation plan
Recommended from our members
A method for measuring dark current electron beams in an RF linac
X-ray fluorescence from thin foils
inserted into the Naval Postgraduate School linac
has been used to measure the integrated electron
beam intensity when the accelerator is operating
with dark current. The measured x-ray flux, the
known inner shell ionization cross sections and
radiative transition probabilities are used to
obtain measurements of dark currents of the order
of 10-14 Amperes. The same arrangement allows
continuous, in-situ energy calibration of our SiLi
detector in the electromagnetic noise environment
of the linac. This technique was originally
developed to perform absolute production
efficiency measurements of parametric x-ray
generation in the 5 - 50 keV range.This work was partially supported by the Defense Nuclear Agency, the Naval Postgraduate School and USDOE SBIR Contract (No. DE-FGO3- 9 1ER8 1099)
Recommended from our members
A concept for Z-dependent microbunching measurements with coherent X-ray transition radiation in a sase FEL
We present an adaptation of the measurements performed in the visible-to-VUV regime of the z-dependent microbunching in a self-amplified spontaneous emission (SASE) free-electron laser (FEL). In these experiments a thin metal foil was used to block the more intense SASE radiation and to generate coherent optical transition radiation (COTR) as one source in a two-foil interferometer. However, for the proposed x-ray SASE FELs, the intense SASE emission is either too strongly transmitted at 1.5 Angstrom or the needed foil thickness for blocking scatters the electron beam too much. Since x-ray transition radiation (XTR) is emitted in an annulus with opening angle 1/g = 36 mrad for 14.09-GeV electrons, we propose using a thin foil or foil stack to generate the XTR and coherent XTR (CXTR) and an annular crystal to wavelength sort the radiation. The combined selectivity in angle and wavelength will favor the CXTR over SASE by about eight orders of magnitude. Time-dependent GINGER simulations support the z-dependent gain evaluation plan
A compact tunable x-ray source based on parametric x-ray generation by moderate energy linacs
Parametric x-radiation can be described as
the diffraction of virtual photons associated with
the electric field of a relativistic charged particle
passing through a crystal. In analogy with Bragg
reflection of x-rays, these diffracted photons
appear as real photons, with an energy which
satisfies Bragg's law for the reflecting crystal
planes. We describe the results of experiments
performed on the Naval Postgraduate School linac
which were designed to explore the basic
properties of PXR in order to assess its potential
application as a compact tunable x-ray source.
Experiments using a mosaic graphite radiator
show that this radiator produced multiple order,
narrow bandwidth reflections from 5 - 45 keV.
The measured production efficiency is found to
exceed that predicted for spectral orders n > 1.
We demonstrated the tunability of PXR by
rotating the crystal in order to change the Bragg
angle relative to the incident 90 MeV electron
beam.This work was partially supported by the Defense Nuclear Agency, the Naval Postgraduate School and USDOE SBIR Contract (No. DE-FG03-9lER81099