79 research outputs found

    Non-linearity observed in the direct sub-ps photoemission regime in Mo

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    The total charge emitted from a polycrystalline Mo surface by 500 fs-264 nm laser pulses has been measured. Though a one-photon photoelectric effect is expected, a non-linear increase of the photoelectric yield was observed as a function of laser peak intensity, confirming earlier observations on Au, W and Zr. The threshold intensity for this non-linearity is 2 between 0.1 and 0.2 GW/ cm . The linear and non-linear regimes were clearly discerned in the experimental data. The non-equilibrium heating of the conduction electrons is considered as the cause of the observed non-linear behaviour. © 1999 Elsevier Science B.V. All rights reserved

    Linear and nonlinear total-yield photoemission observed in the subpicosecond regime in Mo

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    The total charge emitted from a polycrystalline Mo sample by 500 fs laser pulses at normal incidence is measured as a function of the laser peak intensity. Total yield data are taken at wavelengths of 527 and 264 nm. In both cases, a nonlinearity higher than expected is measured. A thermally enhanced regime is clearly observed when using 264 nm pulses for laser peak intensity larger than 0.1--0.2 GW/cm2{\mathrm{G}\mathrm{W}/\mathrm{c}\mathrm{m}}^{2}. This effect is interpreted on the basis of the nonequilibrium heating of the conduction electrons. Pump and probe photoemission data at 527 nm show a significant enhancement of the photoelectric sensitivity when the probe pulse is delayed by 1 ps from the pump. This enhancement is related to the growth of the available electron density induced by the nonequilibrium heating. Single pulse photoemission at this wavelength is not properly explained by a thermally assisted photoemission regime. This may indicate that other processes have a role in determining the photoemission yield

    A study for the characterization of high QE photocathodes

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    Based on our experience on photocathode production, we present in this paper the results of the application of different optical diagnostic techniques on fresh and used photocathodes. These techniques allow studying effects like non uniformity, cathode aging, etc. In particular, photocathode optical parameters and QE characterization, both done at different wavelengths, give fundamentals information for the construction of a model of the photoemission process to be applied to Cs2Te photocathodes. These studies are useful for further improving key cathode features, such as its robustness and lifetime as well as to study and control the photocathodes thermal emittance


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    TRASCO-ADS is a national funded program in which INFN, ENEA, and Italian industries work on the design of an accelerator driven subcritical system for nuclear waste transmutation. TRASCO is the Italian acronym for Transmutation (TRAsmutazione) of Waste (SCOrie). One of the most critical aspects in the design of an Accelerator Driven System is related to the interface region, which is the part of the beamline located between the accelerator, operating under UHV conditions, and the pressurized reactor vessel, consisting of a contained plenum of Pb-Bi eutectic (LBE). A so-called window could separate these two environments, but thermomechanical considerations and radioprotection issues point out that this component could be critical. In the windowless interface, no window is located between the linac and the spallation target. Only a suitable pumping and trapping system, for the gases and the vapors outcoming from LBE, divides the UHV accelerator and the spallation target vacuum. Vacuum gas dynamics theoretical considerations and calculations are presented in this article. The need for a validation of the theoretical models gave the motivation for an experimental work, whose results are also discussed. Scale-up of the experimental setup to the full system needs accurate analyses for a proper dimensioning of the system in the interface region

    Performance analysis of the European X-ray Free Electron Laser 3.9 GHz superconducting cavities

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    The limits of performance of the European XFEL 3.9 GHz superconducting cavities were investigated. Most cavities exhibited high field Q slope, reaching the breakdown field at approximately 22  MV/m22\text{ }\text{ }\mathrm{MV}/\mathrm{m}. We hypothesize that this limit is a feature of high frequency cavities and can be explained by a thermal model incorporating field dependent surface resistance. The results obtained from simulations were in good agreement with experimental data obtained at 2 K

    GeV-Class two-fold CW linac driven by an arc-compressor

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    We present a study of an innovative scheme to generate high repetition rate (MHz-class) GeV electron beams by adopting a two-pass two-way acceleration in a super-conducting Linac operated in Continuous Wave (CW) mode. The beam is accelerated twice in the Linac by being re-injected, after the first pass, in opposite direction of propagation. The task of recirculating the electron beam is performed by an arc compressor composed by 14 Double Bend Achromat (DBA). In this paper, we study the main issues of the two-fold acceleration scheme, the electron beam quality parameters preservation (emittance, energy spread), together with the bunch compression performance of the arc compressor, aiming to operate an X-ray Free Electron Laser. The requested power to supply the cryogenic plant and the RF sources is also significantly reduced w.r.t a conventional one-pass SC Linac for the same final energy

    Towards a muon collider

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    A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work

    Conceptual Design of a Soft X‚Äźray SASE‚ÄźFEL Source

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    FELs based on SASE are believed to be powerful tools to explore the frontiers of basic sciences, from physics to chemistry to biology. Intense R&D programs have started in the USA and Europe in order to understand the SASE physics and to prove the feasibility of these sources. The allocation of considerable resources in the Italian National Research Plan (PNR) brought about the formation of a CNR‚ÄźENEA‚ÄźINFN‚ÄźUniversity of Roma "Tor Vergata" study group. A conceptual design study has been developed and possible schemes for linac sources have been investigated, bringing to the SPARX proposal. We report in this paper the results of a preliminary start to end simulation concerning one option we are considering based on an S‚Äźband normal conducting linac with high brightness photoinjector integrated in a RF compressor
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