L. Catani

Characterization of the THz radiation source at the Frascati linear accelerator

The linac driven coherent THz radiation source at the SPARC-LAB test facility is able to deliver broadband THz pulses with femtosecond shaping. In addition, high peak power, narrow spectral bandwidth THz radiation can be also generated, taking advantage of advanced electron beam manipulation techniques, able to generate an adjustable train of electron bunches with a sub-picosecond length and with sub-picosecond spacing. The paper reports on the manipulation, characterization, and transport of the electron beam in the bending line transporting the beam down to the THz station, where different coherent transition radiation spectra have been measured and studied with the aim to optimize the THz radiation performances.

The SPARC linear accelerator based terahertz source

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.

A large distributed digital camera system for accelerator beam diagnostics

Optical diagnostics, providing images of accelerated particle beams using radiation emitted by particles impinging a radiator, typically a fluorescent screen, has been extensively used, especially on electron linacs, since the 1970s. Higher intensity beams available in the last decade allow extending the use of beam imaging techniques to perform precise measurements of important beam parameters such as emittance, energy, and energy spread using optical transition radiation (OTR). OTR-based diagnostics systems are extensively used on the superconducting TESLA Test Facility (TTF) linac driving the vacuum ultraviolet free electron laser (VUV-FEL) at the Deutsches Elektronen-Synchrotron facility. Up to 30 optical diagnostic stations have been installed at various positions along the 250-m-long linac, each equipped with a high-performance digital camera. This paper describes the new approach to the design of the hardware and software setups required by the complex topology of such a distributed camera system.

Niobium Coating of Cavities Using Cathodic Arc

Niobium thin film coated copper RF cavities are an interesting alternative to niobium bulk cavities for the development of high performance superconducting accelerators. The main limiting factor in their use is the degradation of the quality factor Q with increasing accelerating field (the ldquoQ-Sloperdquo). To try and overcome this limitation, we have developed an alternative coating technique based on a Cathodic Arc system working under UHV conditions (UHVCA). High quality Nb samples have been synthesized under different deposition angles and their characteristics are presented. The UHVCA technique has been used to deposit 1.3 GHz TESLA-type single cell cavities. To further improve cavity performance the first critical field has to be enhanced. The use of multilayers consisting of alternating insulating and superconducting layers may produce the desired enhancement providing that the superconducting layer thickness is smaller than the London penetration depth. To this aim, we present also the experimental characterization of the superconducting properties (TC, BC1) of Nb/AlOx/Nb multilayers.

Analysis of optical transition radiation emitted by a 1 MeV electron beam and its possible use as diagnostic tool

Abstract The main features of optical transition radiation (OTR) backward emitted by a 1 MeV electron beam crossing a vacuum-to-metal boundary are presented. The possible use of OTR as a diagnostic tool for such a low energy beam is discussed, and some preliminary experimental data are presented.

Design and characterization of a movable emittance meter for low-energy electron beams

In order to characterize and optimize the beam emittance compensation scheme [L. Serafini and J. B. Rosenzweig, Phys. Rev. E 55, 7565 (1997)] of the Sorgente Pulsata Autoamplificata di Radiazione Coerente project [D. Alesini et al., Nucl. Instrum. Methods Phys. Res. A 507, 345 (2003)] high brightness preinjector a system to accurately measure the beam rms emittance evolution downstream of the rf gun has been developed. Since in a space charge dominated beam the quadrupole-scan method is not applicable, a movable emittance measurement device has been built based on the pepper-pot technique. The device consists of a double system of horizontal and vertical slit arrays and a downstream screen, all installed on a longitudinally movable support equipped with bellows and spanning the ≈1.2m long drift space between gun and first accelerating section. The system allows the measuring of the beam rms emittance all along the spanned region so as to accurately reconstruct its evolution along the beam trajectory. More...

Purity of Nb and Pb Films Deposited by an Ultrahigh Vacuum Cathodic Arc

This paper reports on recent progress in the application of ultrahigh vacuum arc technology, which was proposed as an alternative solution for the deposition of thin superconducting films of pure niobium upon the inner surfaces of RF cavities designed for particle accelerators. New experiments were conducted to deposit superconducting films of pure niobium and lead needed for the modern accelerator technology. Presented scanning electron microscopy, scattered ion mass spectroscopy technique, and glow discharge-optical emission spectroscopy studies of such produced Nb and Pb films showed that the concentration level of impurities is lower than 0.2% and 1%, respectively. Achieved cleanliness goes together with outstanding superconducting properties. The main experimental results and characteristics of arc-deposited thin superconducting films are discussed, and the progress achieved recently in the formation of such films is presented.

On line calorimetric measurement of the quality factor of superconducting accelerator cavities

Abstract A comparative precise method to measure the Q factor of installed superconducting cavities is described. Data taken on the cavities of the 25 MeV s

Experimental results with the SPARC emittance-meter

The SPARC project foresees the realization of a high brightness photo-injector to produce a 150-200 MeV electron beam to drive a SASE-FEL in the visible light. As a first stage of the commissioning a complete characterization of the photoinjector has been accomplished with a detailed study of the emittance compensation process downstream the gun-solenoid system with a novel beam diagnostic device, called emittance meter. In this paper we report the results obtained so far including the first experimental observation of the double emittance minimum effect on which is based the optimised matching with the SPARC linac.

Experimental Testing of Dynamically Optimized Photoelectron Beams

We discuss the design of and initial results from an experiment in space‐charge dominated beam dynamics which explores a new regime of high‐brightness electron beam generation at the SPARC photoinjector. The scheme under study employs the tendency of intense electron beams to rearrange to produce uniform density, giving a nearly ideal beam from the viewpoint of space charge‐induced emittance. The experiments are aimed at testing the marriage of this idea with a related concept, emittance compensation. We show that this new regime of operating photoinjector may be the preferred method of obtaining highest brightness beams with lower energy spread. We discuss the design of the experiment, including developing of a novel time‐dependent, aerogel‐based imaging system. This system has been installed at SPARC, and first evidence for nearly uniformly filled ellipsoidal charge distributions recorded.