260 research outputs found
Electron Beam Dynamics in the 50 MeV ThomX Compact Storage Ring
International audienceThomX is a high flux compact X-ray source based on Compton back scattering between a relativistic electron beam and an intense laser pulse. To increase the repetition rate, the electron beam is stored in a ring. The main drawback of such a scheme is the low energy of the electrons regarding collective effects and intrabeam scattering. These effects tend to enlarge or even disrupt the stored bunch and they limit its charge, especially in a system where damping plays a negligible role. Thus such collective effects reduce the maximum X-ray flux and it is important to investigate them to predict the performance of this type of X-ray source. In addition, the Compton back scattering acts on the electron beam by increasing its energy spread. This presentation will show firstly the impact of collective effects on the electron beam, essentially during the first turns when they are the most harmful. Then, the reduction of the X-ray flux due to Compton back scattering and intrabeam scattering will be investigated on a longer time scale
The Transparency of Solar Coronal Active Regions
Resonance scattering has often been invoked to explain the disagreement
between the observed and predicted line ratios of Fe XVII 15.01 A to Fe XVII
15.26 A (the ``3C/3D'' ratio). In this process photons of 15.01, with its much
higher oscillator strength, are preferentially scattered out of the line of
sight, thus reducing the observed line ratio. Recent laboratory measurements,
however, have found significant inner-shell Fe XVI lines at 15.21 and 15.26
Angstroms, suggesting that the observed 3C/3D ratio results from blending.
Given our new understanding of the fundamental spectroscopy, we have
re-examined the original solar spectra, identifying the Fe XVI 15.21 line and
measuring its flux to account for the contribution of Fe XVI to the 15.26 flux.
Deblending brings the 3C/3D ratio into good agreement with the experimental
ratio; hence, we find no need to invoke resonance scattering. Low opacity in Fe
XVII 15.01 also implies low opacity for Fe XV 284.2, ruling out resonance
scattering as the cause of the fuzziness of TRACE and SOHO EIT 284-Angstrom
images. The images must, instead, be unresolved due to the large number of
structures at this temperature. Insignificant resonance scattering implies that
future instruments with higher spatial resolution could resolve the active
region plasma into its component loop structures.Comment: accepted to Ap J Letter
Compact Ring for the ThomX-ray Source
THPE060International audienceOne advantage of X-ray sources based on Compton Back Scattering (CBS) processes is that such compact machines can produce an intense flux of monochromatic X-rays. CBS results from collisions between laser pulses and relativistic electron bunches. Aiming at high X-ray flux, one possible configuration combining a low emittance linear accelerator with a compact storage ring and a high gain laser cavity has been adopted by the ThomX project. We present here the main ring lattice characteristics in terms of baseline optics, possible other tunings such as low or negative momentum compaction, and orbit correction schemes. In addition, non-linear beam dynamics aspects including fringe field components as well as higher multipole tolerances are presented
A Compact Ring for Thom X-Ray Source
International audienceThe goal of X-ray sources based on Compton back scattering processes is to develop a compact device, which could produce an intense flux of monochromatic X-rays. Compton back-scattering resuls from collisions between laser pulses and relativistic electron bunches. Due to the relative low value of the Compton cross section, a high charge electron beam, a low emittance and a high focusing at the interaction point are required for the electron beam. In addition, the X-ray flux is related to the characteristics of the electron beam, which are themselves dynamically affected by the Compton interaction. One possible configuration is to inject frequently into a storage ring with a low emittance linear accelerator without waiting for the synchrotron equilibrium. As a consequence, the optics should be designed taking into account the characteristics of the electron beam from the linear accelerator. The accelerator ring design for a 50 MeV electron beam, aiming at producing a flux higher than 1013 ph/s, will be presented
LUNEX5 : A FEL PROJECT TOWARDS THE FIFTH GENERATION IN FRANCE
ISBN978-3-95450-117-5 - http://accelconf.web.cern.ch/AccelConf/FEL2011/papers/tupa09.pdfInternational audienc
First Application of the Fe XVII I(17.10 A)/I(17.05 A) Line Ratio to Constrain the Plasma Density of a Cosmic X-ray Source
We show that the Fe XVII I(17.10 A)/I(17.05 A) line ratio observed in the
Chandra HETG spectrum of the intermediate polar EX Hydrae is significantly
smaller than that observed in the Sun or other late-type stars. Using the
Livermore X-ray Spectral Synthesizer, which calculates spectral models of
highly charged ions based on HULLAC atomic data, we find that the observed
I(17.10 A)/I(17.05 A) line ratio can be explained if the plasma density n_e >
3x10^{14} cm^{-3}. However, if photoexcitation is included in the level
population kinetics, the line ratio can be explained for any density if the
photoexcitation temperature T_bb > 55 kK. For photoexcitation to dominate the
Fe XVII level population kinetics, the relative size of the hotspot on the
white dwarf surface must be f < 2%. This constraint and the observed X-ray flux
requires a density n > 2x10^{14} cm^{-3} for the post-shock flow. Either way,
then, the Chandra HETG spectrum of EX Hya requires a plasma density which is
orders of magnitude greater than that observed in the Sun or other late-type
stars.Comment: 13 pages including 1 table and 4 encapsulated postscript figures;
LaTeX format, uses aastex.cls; accepted on 2001 June 27 for publication in
The Astrophysical Journa
CHIANTI - an Atomic Database for Emission Lines. Paper VI: Proton Rates and Other Improvements
The CHIANTI atomic database contains atomic energy levels, wavelengths,
radiative transition probabilities and electron excitation data for a large
number of ions of astrophysical interest. Version 4 has been released, and
proton excitation data is now included, principally for ground configuration
levels that are close in energy. The fitting procedure for excitation data,
both electrons and protons, has been extended to allow 9 point spline fits in
addition to the previous 5 point spline fits. This allows higher quality fits
to data from close-coupling calculations where resonances can lead to
significant structure in the Maxwellian-averaged collision strengths. The
effects of photoexcitation and stimulated emission by a blackbody radiation
field in a spherical geometry on the level balance equations of the CHIANTI
ions can now be studied following modifications to the CHIANTI software. With
the addition of H I, He I and N I, the first neutral species have been added to
CHIANTI. Many updates to existing ion data-sets are described, while several
new ions have been added to the database, including Ar IV, Fe VI and Ni XXI.
The two-photon continuum is now included in the spectral synthesis routines,
and a new code for calculating the relativistic free-free continuum has been
added. The treatment of the free-bound continuum has also been updated.Comment: CHIANTI is available at http://wwwsolar.nrl.navy.mil/chianti.htm
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