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We report on the growth and characterization of a new class of photocathode structures for use as electron sources to produce high brightness electron beams for accelerator applications. The sources are realized using III-nitride materials and are designed to leverage the strong polarization field, which is characteristic of this class of materials when grown in their wurtzite crystal structure, to produce a negative electron affinity condition without the use of Cs, possibly allowing these materials to be operated in radio frequency guns. A Quantum Efficiency (QE) of about 1 × 10 − 3 and an emitted electrons' Mean Transverse Energy (MTE) of about 100 meV are measured at a wavelength of 265 nm. In a vacuum level of 3 × 10 − 10 Torr, the QE does not decrease after more than 24 h of continuous operation. The lowest MTE of about 50 meV is measured at 300 nm along with a QE of 1.5 × 10 − 5 . Surface characterizations reveal a possible contribution to the MTE from surface morphology, calling for more detailed studies. [ABSTRACT FROM AUTHOR]

Abstract: Mg-based films have been prepared by pulsed laser deposition technique for photocathode applications. We have investigated the influence of pulse laser duration on morphology and photoemissive properties. Two laser sources have been used, generating pulses of 30ns at 308nm (XeCl excimer laser), 5ps and 500fs at 248nm (KrF excimer laser) to grow Mg films onto Si and Cu substrates in high vacuum (∼10−7 Pa) and at room temperature. Morphological investigations carried out by scanning electron microscopy (SEM) have revealed that, in our experimental conditions, the number and the mean size of the droplets on the films surfaces decreases as the pulse laser duration shortens. The contamination level of Mg film surfaces have been studied by energy dispersive X-ray spectroscopy (EDX). The photoelectron performances in terms of quantum efficiency (QE) and emission stability have been tested in a UHV DC photodiode cell (10−7 Pa). Measures of the QE of the samples surfaces have revealed a decrease on the initial value for Mg-based photocathodes prepared by fs laser (from 7.8×10−4 to 6.6×10−4) PLD with respect to ps (from 6.2×10−4 to 7.4×10−4) and ns lasers (from 5.0×10−4 to 1.6×10−3). A comparison among Mg-based photocathodes prepared by ns, ps and fs PLD for the production of high brightness electron beams has been presented and discussed. [Copyright &y& Elsevier]

Ultra-short electron beams, produced through the velocity bunching compression technique, are used to drive the SPARC linear accelerator based source, which relies on the emission of coherent transition radiation in the terahertz range. This paper reports on the main features of this radiation, as terahertz source, with spectral coverage up to 5 THz and pulse duration down to 200 fs, with an energy per pulse of the order of several micro-joule, and as electron beam longitudinal diagnostics. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we review the status of bright electron sources. High peak current (up to kA) low emittance (< 1 mm rad) electron beams have been one of the critical components in the development of XFELs. The outlook for the field is even more promising as progress in the understanding of photoemission physics, development of novel photocathode materials, gun and laser technology, enable further progress in advanced light sources as well as novel applications such as ultrafast electron diffraction and microscopy. We outline here the more recent research trends which pave the way for potentially orders of magnitude brightness improvements with respect to the current state-of-the-art. [ABSTRACT FROM AUTHOR]

Abstract: The advance in laser–plasma acceleration techniques pushes the regime of the resulting accelerated particles to higher energies and intensities. In particular, the upcoming experiments with the 250TW laser at the FLAME facility of the INFN Laboratori Nazionali di Frascati, will enter the GeV regime with more than 100pC of electrons. At the current status of understanding of the acceleration mechanism, relatively large angular and energy spreads are expected. There is therefore the need for developing a device capable to measure the energy of electrons over three orders of magnitude (few MeV to few GeV), with still unknown angular divergences. Within the PlasmonX experiment at FLAME, a spectrometer is being constructed to perform these measurements. It is made of an electro-magnet and a screen made of scintillating fibers for the measurement of the trajectories of the particles. The large range of operation, the huge number of particles and the need to focus the divergence, present challenges in the design and construction of such a device. We present the design considerations for this spectrometer that lead to the use of scintillating fibers, multichannel photo-multipliers and a multiplexing electronics, a combination which is innovative in the field. We also present the experimental results obtained with a high intensity electron beam performed on a prototype at the LNF beam test facility. [Copyright &y& Elsevier]

Abstract: The PLasma Acceleration and MONochromatic X-ray generation (PLASMONX) project foresees the installation at LNF of a 0.3PW (6J, 20fs pulse) Ti:Sa laser system, named Frascati Laser for Acceleration and Multidisciplinary Experiments (FLAME), to operate in close connection with the existent SPARC electron photo-injector, allowing for advanced laser/e-beam interaction experiments. Among the foreseen scientific activities, a Thomson scattering experiment between the SPARC electron bunch and the high power laser will be performed. At the present time the linac has been tested and the electron beam characterized up to the maximum operating energy (150MeV). The beam lines transporting the beam to the interaction chamber with the laser have been designed. The electron final focusing system, featuring a quadrupole triplet and large radius solenoid magnet (ensuring an e-beam waist of 5–10μm) as well as the whole interaction chamber layout has been defined. The optical transfer line issues: transport up to the interaction; tight focusing; diagnostics and fine positioning; have been solved within the final design. The construction of the building hosting the laser has been completed; delivering and installation of the laser, as much of the beam lines elements will take place in the next months. [Copyright &y& Elsevier]