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Träfflista för sökning "L773:1098 4402 OR L773:1098 4402 "

Sökning: L773:1098 4402 OR L773:1098 4402

  • Resultat 1-10 av 54
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1.
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2.
  • Adli, E., et al. (författare)
  • X-band rf power production and deceleration in the two-beam test stand of the Compact Linear Collider test facility
  • 2011
  • Ingår i: Physical Review Special Topics - Accelerators and Beams. - 1098-4402. ; 14:8, s. 081001-
  • Tidskriftsartikel (refereegranskat)abstract
    • We discuss X-band rf power production and deceleration in the two-beam test stand of the CLIC test facility at CERN. The rf power is extracted from an electron drive beam by a specially designed power extraction structure. In order to test the structures at high-power levels, part of the generated power is recirculated to an input port, thus allowing for increased deceleration and power levels within the structure. The degree of recirculation is controlled by a splitter and phase shifter. We present a model that describes the system and validate it with measurements over a wide range of parameters. Moreover, by correlating rf power measurements with the energy lost by the electron beam, as measured in a spectrometer placed after the power extraction structure, we are able to identify system parameters, including the form factor of the electron beam. The quality of the agreement between model and reality gives us confidence to extrapolate the results found in the present test facility towards the parameter regime of CLIC.
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3.
  • Angelova, G., et al. (författare)
  • Observation of two-dimensional longitudinal-transverse correlations in an electron beam by laser-electron interactions
  • 2008
  • Ingår i: Physical Review Special Topics - Accelerators and Beams. - 1098-4402. ; 11:7
  • Tidskriftsartikel (refereegranskat)abstract
    • During the preparatory work for the optical-replica synthesizer experiment in the free-electron laser FLASH at DESY, we were able to superimpose a short, approximately 200 fs long pulse from a frequencydoubled mode-locked erbium laser with titanium-sapphire amplifier and an approximately 20 ps long electron bunch in an undulator. This induces an energy modulation in a longitudinal slice of the electron bunch. A magnetic chicane downstream of the undulator converts the energy modulation into a density modulation within the slice that causes the emission of coherent optical transition radiation from a silver-coated silicon screen. Varying the relative timing between electron and laser, we use a camera to record two-dimensional images of the slices as a function of the longitudinal position within the electron bunch.
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4.
  • Apyan, A., et al. (författare)
  • Coherent bremsstrahlung, coherent pair production, birefringence, and polarimetry in the 20-170 GeV energy range using aligned crystals
  • 2008
  • Ingår i: Physical Review Special Topics - Accelerators and Beams. - 1098-4402. ; 11:4, s. 041001-
  • Tidskriftsartikel (refereegranskat)abstract
    • The processes of coherent bremsstrahlung (CB) and coherent pair production (CPP) based on aligned crystal targets have been studied in the energy range 20-170 GeV. The experimental arrangement allowed for measurements of single photon properties of these phenomena including their polarization dependences. This is significant as the theoretical description of CB and CPP is an area of active debate and development. With the approach used in this paper, both the measured cross sections and polarization observables are predicted very well. This indicates a proper understanding of CB and CPP up to energies of 170 GeV. Birefringence in CPP on aligned crystals is applied to determine the polarization parameters in our measurements. New technologies for high-energy photon beam optics including phase plates and polarimeters for linear and circular polarization are demonstrated in this experiment. Coherent bremsstrahlung for the strings-on-strings (SOS) orientation yields a larger enhancement for hard photons than CB for the channeling orientations of the crystal. Our measurements and our calculations indicate low photon polarizations for the high-energy SOS photons.
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5.
  • Bagdasarian, Z., et al. (författare)
  • Measuring the polarization of a rapidly precessing deuteron beam
  • 2014
  • Ingår i: Physical Review Special Topics - Accelerators and Beams. - 1098-4402. ; 17:5, s. 052803-
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper describes a time-marking system that enables a measurement of the in-plane (horizontal) polarization of a 0.97-GeV/c deuteron beam circulating in the Cooler Synchrotron (COSY) at the Forschungszentrum Julich. The clock time of each polarimeter event is used to unfold the 120-kHz spin precession and assign events to bins according to the direction of the horizontal polarization. After accumulation for one or more seconds, the down-up scattering asymmetry can be calculated for each direction and matched to a sinusoidal function whose magnitude is proportional to the horizontal polarization. This requires prior knowledge of the spin tune or polarization precession rate. An initial estimate is refined by resorting the events as the spin tune is adjusted across a narrow range and searching for the maximum polarization magnitude. The result is biased toward polarization values that are too large, in part because of statistical fluctuations but also because sinusoidal fits to even random data will produce sizable magnitudes when the phase is left free to vary. An analysis procedure is described that matches the time dependence of the horizontal polarization to templates based on emittance-driven polarization loss while correcting for the positive bias. This information will be used to study ways to extend the horizontal polarization lifetime by correcting spin tune spread using ring sextupole fields and thereby to support the feasibility of searching for an intrinsic electric dipole moment using polarized beams in a storage ring. This paper is a combined effort of the Storage Ring EDM collaboration and the JEDI collaboration.
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6.
  • Biedron, Sandra G., et al. (författare)
  • Impact of electron beam quality on nonlinear harmonic generation in high-gain free-electron lasers
  • 2002
  • Ingår i: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 5:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Nonlinear harmonic generation can be a very useful and important phenomenon for single-pass free-electron lasers (FELs) operating in the high-gain regime. Strong bunching at the fundamental wavelength and its associated higher harmonic content allow significant radiation at shorter wavelengths to be emitted without serious effects upon the output power at the fundamental. Here, we analyze the relative sensitivities to beam quality variations of the output fundamental and harmonic powers for a visible-wavelength FEL operating in the high-gain regime.
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7.
  • Bogan, M. J., et al. (författare)
  • Single-shot femtosecond x-ray diffraction from randomly oriented ellipsoidal nanoparticles
  • 2010
  • Ingår i: Physical Review Special Topics - Accelerators and Beams. - 1098-4402. ; 13:9, s. 094701-
  • Tidskriftsartikel (refereegranskat)abstract
    • Coherent diffractive imaging of single particles using the single-shot "diffract and destroy" approach with an x-ray free electron laser (FEL) was recently demonstrated. A high-resolution low-noise coherent diffraction pattern, representative of the object before it turns into a plasma and explodes, results from the interaction of the FEL with the particle. Iterative phase retrieval algorithms are used to reconstruct two-dimensional projection images of the object from the recorded intensities alone. Here we describe the first single-shot diffraction data set that mimics the data proposed for obtaining 3D structure from identical particles. Ellipsoidal iron oxide nanoparticles (250 nm x 50 nm) were aerosolized and injected through an aerodynamic lens stack into a soft x-ray FEL. Particle orientation was not controlled with this injection method. We observed that, at the instant the x-ray pulse interacts with the particle, a snapshot of the particle's orientation is encoded in the diffraction pattern. The results give credence to one of the technical concepts of imaging individual nanometer and subnanometer-sized objects such as single molecules or larger clusters of molecules using hard x-ray FELs and will be used to help develop robust algorithms for determining particle orientations and 3D structure.
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8.
  • Bruce, Roderik, et al. (författare)
  • Beam losses from ultraperipheral nuclear collisions between Pb-208(82+) ions in the Large Hadron Collider and their alleviation
  • 2009
  • Ingår i: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 12:7
  • Tidskriftsartikel (refereegranskat)abstract
    • Electromagnetic interactions between colliding heavy ions at the Large Hadron Collider (LHC) at CERN will give rise to localized beam losses that may quench superconducting magnets, apart from contributing significantly to the luminosity decay. To quantify their impact on the operation of the collider, we have used a three-step simulation approach, which consists of optical tracking, a Monte Carlo shower simulation, and a thermal network model of the heat flow inside a magnet. We present simulation results for the case of Pb-208(82+) ion operation in the LHC, with focus on the ALICE interaction region, and show that the expected heat load during nominal Pb-208(82+) operation is 40% above the quench level. This limits the maximum achievable luminosity. Furthermore, we discuss methods of monitoring the losses and possible ways to alleviate their effect.
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9.
  • Bruce, Roderik, et al. (författare)
  • Measurements of heavy ion beam losses from collimation
  • 2009
  • Ingår i: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 12:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The collimation efficiency for Pb-208(82+) ion beams in the LHC is predicted to be lower than requirements Nuclear fragmentation and electromagnetic dissociation in the primary collimators create fragments with a wide range of Z/A ratios, which are not intercepted by the secondary collimators but lost where the dispersion has grown sufficiently large. In this article we present measurements and simulations of loss patterns generated by a prototype LHC collimator in the CERN SPS. Measurements were performed at two different energies and angles of the collimator. We also compare with proton loss maps and find a qualitative difference between Pb-208(82+) ions and protons, with the maximum loss rate observed at different places in the ring. This behavior was predicted by simulations and provides a valuable benchmark of our understanding of ion beam losses caused by collimation.
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10.
  • Bungau, Cristian, et al. (författare)
  • Induced activation in accelerator components
  • 2014
  • Ingår i: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 17:8
  • Tidskriftsartikel (refereegranskat)abstract
    • The residual activity induced in particle accelerators is a serious issue from the point of view of radiation safety as the long-lived radionuclides produced by fast or moderated neutrons and impact protons cause problems of radiation exposure for staff involved in the maintenance work and when decommissioning the facility. This paper presents activation studies of the magnets and collimators in the High Energy Beam Transport line of the European Spallation Source due to the backscattered neutrons from the target and also due to the direct proton interactions and their secondaries. An estimate of the radionuclide inventory and induced activation are predicted using the GEANT4 code.
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  • Resultat 1-10 av 54

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