22 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
Interference of diffraction and transition radiation and its application as a beam divergence diagnostic
The article of record as published may be found at http://dx.doi.org/10.1103/PhysRevSTAB.9.052802We have observed the interference of optical diffraction radiation (ODR) and optical transition radiation (OTR) produced by the interaction of a relativistic electron beam with a micromesh foil and a mirror. The production of forward directed ODR from electrons passing through the holes and wires of the mesh and their separate interactions with backward OTR from the mirror are analyzed with the help of a simulation code. By careful choice of the micromesh properties, mesh-mirror spacing, observation wavelength, and filter band pass, the interference of the ODR produced from the unperturbed electrons passing through the open spaces of the mesh and OTR from the mirror are observable above a broad incoherent background from interaction of the heavily scattered electrons passing through the mesh wires. These interferences (ODTRI) are sensitive to the beam divergence and can be used to directly diagnose this parameter. We compare experimental divergence values obtained using ODTRI, conventional OTRI, for the case when front foil scattering is negligible, and computed values obtained from transport code calculations and multiple screen beam size measurements. We obtain good agreement in all cases.This work is supported by the Office of Naval Research and the DOD Joint Technology Offic
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
DYNAMIC DUROMETER MEASUREMENT OF YOUNG'S MODULUS AND LOSS FACTOR
The Shore hardness tester is used extensively throughout industry to determine the static modulus of materials. The new apparatus described here extends the capability of an indentor type tester into the dynamic regime, and provides a measurement of the dynamic shear or Young's modulus and loss factor as a function of frequency. The instrument, model and data of typical rubber samples are given and compared to other dynamic measurements.L'essayeur de dureté Shore est utilisé du manière étendue dans l'industrie enfin de déterminer le coefficient statique des matériaux. Ce nouvelle appareil décrit ici étend les capacités d'usage l'essayeur de type dentelure dans le régime dynamique, et donne le mesurage de cisaillement dynamique ou coefficient Young et le facteur d'amortissement en fonction de la fréquence. L'appareil, le modèle et les donnés d'échantillon de caoutchouc typiques sont décrits et sont comparés avec différents mesures dynamiques
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
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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)
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
Polarized angular distributions of parametric x radiation and vacuum-ultraviolet transition radiation from relativistic electrons
We present quantifiable images of the angular distribution (AO's) of parametric X radiation (PXR) and vacuum-ultraviolet transition radiation (vuv TR) from 230 MeV electrons interacting with a silicon crystal. Both AD's are highly polarized. The vuv TR and optical TR data provide measurements of the beam energy and effective divergence angle. Using these quantities and separately known values of the electronic susceptibility |Xo|, we show that the measured PXR AD is in good agreement with the predictions of single crystal theory. Our analysis suggests a method to measure |Xo| using PXR AD's.Ths work was sponsored in part by DOE SBIR Grant No. DE-FG03-91er80199; NCI SBIR Grant no. 1-R43-CA60207-01 and the Canadian Natural Science and Engineering Research Counci
Parametric X-ray radiation for calibration of X-ray space telescopes and generation of several X-ray beams
ThéorieThe setup based on a moderate energy linear accelerator (linac) is proposed to provide users with a tunable, quasi-monochromatic, linearly polarized X-ray beam. The effect of parametric X-ray radiation (PXR) from relativistic electrons in a crystal is used in an X-ray source. The application of the setup for calibration of X-ray space telescopes and other equipment is considered. The setup allows calibration of angular, spectral, polarization parameters of telescopes with smooth tuning of X-ray energy from several keV to hundreds of keV. Estimates of X-ray flux intensities and spectral line widths on the telescope aperture at a distance of several hundred meters are presented. Besides, the PXR-based facility for simultaneous generation of several X-ray beams is proposed
INTERACTION OF AN INTENSE RELATIVISTIC ELECTRON BEAM WITH THE ATMOSPHERE
No abstract availabl