2,105 research outputs found
Microscopic kinetic analysis of space-charge induced optical microbunching in a relativistic electron beam
Longitudinal space-charge forces from density fluctuations generated by shot noise can be a major source of microbunching instability in relativistic high brightness electron beams. The gain in microbunching due to this effect is broadband, extending at least up to optical frequencies, where the induced structure on the beam distribution gives rise to effects such as coherent optical transition radiation. In the high-frequency regime, theoretical and computational analyses of microbunching formation require a full three-dimensional treatment. In this paper we address the problem of space-charge induced optical microbunching formation in the high-frequency limit when transverse thermal motion due to finite emittance is included for the first time. We derive an analytical description of this process based on the beam's plasma dielectric function. We discuss the effect of transverse temperature on the angular distribution of microbunching gain and its connection to the physics of Landau damping in longitudinal plasma oscillations. Application of the theory to a relevant experimental scenario is discussed. The analytical results obtained are then compared to the predictions arising from high resolution three-dimensional molecular dynamics simulations
Comparative study of nonideal beam effects in high gain harmonic generation and self-seeded free electron lasers
In this paper we investigate and compare the properties of two narrow-bandwidth free-electron laser (FEL) schemes, one using self-seeding and the other high gain harmonic generation (HGHG). The two systems have been thoroughly studied analytically and numerically in the past. The aim of this work is to compare their performances when the FEL is driven by an electron beam with nonideal properties, thus including effects such as shot-to-shot energy fluctuations and nonlinear energy chirp. In both cases nonlinearities produce a bandwidth larger than the Fourier transform limited value. However, our analysis indicates that, for approximately the same output power levels, the self-seeding scheme is less affected than the HGHG scheme by quadratic energy chirps in the electron beam longitudinal phase space. This is confirmed by a specific numerical example corresponding to SPARX parameters where the electron beam was optimized to minimize the FEL gain length. The work has been carried out with the aid of the time dependent FEL codes GENESIS 1.3 (3D) and PERSEO (1D)
Longitudinal dispersion of orbital angular momentum modes in high-gain free-electron lasers
The physical effects of optical mode dispersion in the electron beam of a free-electron laser are investigated for modes that carry orbital angular momentum. The analysis is performed using a derived equivalence between two different formulations that describe the radiation fields in the linear regime
Nonlinearly Shaped Pulses in Photoinjectors and Free-Electron Lasers
Photoinjectors and Free Electron Lasers (FEL) are amongst the most advanced
systems in accelerator physics and have consistently pushed the boundaries of
emittance and x-ray peak power. In this paper, laser shaping at the cathode is
proposed to further lower the emittance and reduce electron beam tails, which
would result in brighter x-ray production. Using dispersion controlled
nonlinear shaping (DCNS), laser pulses and beam dynamics were simulated in
LCLS-II. The photoinjector emittance was optimized and the resulting e-beam
profiles were then simulated and optimized in the linac. Finally, the expected
FEL performance is estimated and compared to the current technology: Gaussian
laser pulses on the cathode. The e-beams produced by DCNS pulses show a
potential for 35% increase in x-ray power per pulse during SASE when compared
to the standard Gaussian laser pulses
RETRACTED: Ehlers-Danlos syndrome caused by the c.934C>T, p. Arg312Cys mutation in COL1A1 gene: an Italian family without cardiovascular events
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Characterization of Single-Shot Attosecond Pulses with Angular Streaking Photoelectron Spectra
Most of the traditional attosecond pulse retrieval algorithms are based on a so-called attosecond streak camera technique, in which the momentum of the electron is shifted by an amount depending on the relative time delay between the attosecond pulse and the streaking infrared pulse. Thus, temporal information of the attosecond pulse is encoded in the amount of momentum shift in the streaked photoelectron momentum spectrogram S(p, Ï„), where p is the momentum of the electron along the polarization direction and Ï„ is the time delay. An iterative algorithm is then employed to reconstruct the attosecond pulse from the streaking spectrogram. This method, however, cannot be applied to attosecond pulses generated from free-electron x-ray lasers where each single shot is different and stochastic in time. However, using a circularly polarized infrared laser as the streaking field, a two (or three)-dimensional angular streaking electron spectrum can be used to retrieve attosecond pulses for each shot, as well as the time delay with respect to the circularly polarized IR field. Here we show that a retrieval algorithm previously developed for the traditional streaking spectrogram can be modified to efficiently characterize single-shot attosecond pulses. The methods have been applied to retrieve 188 single shots from recent experiments. We analyze the statistical behavior of these 188 pulses in terms of pulse duration, bandwidth, pulse peak energy, and time delay with respect to the IR field. The retrieval algorithm is efficient and can be easily used to characterize a large number of shots in future experiments for attosecond pulses at free-electron x-ray laser facilities
Thaumatotibia leucotreta (Meyrick) (Lepidoptera Tortricidae) intercepted for the first time in Italy
In June 2014, Thaumatotibia leucotreta (Meyrick) (Lepidoptera Tortricidae) was found during the inspection of the Italian Phytosanitary Service of Tuscany Region in the port of Leghorn, in a container from South Africa containing Navel oranges. The degree of damage is high, reaching the 2% of the harvested fruits. This is the first interception of this polyphagous pest for Italy
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