Design of an X-band constant impedance LINAC for compact light project

Within the framework of Horizon 2020 project, Compact Light, in order to provide a high performance, high-gradient X-band technology, for the new generation of hard X-ray FEL, a travelling wave (TW) Linac, working on 2pi/3 mode at 11.9952 GHz, fed by two types of asymmetrically couplers, has been designed. The design was performed using CST Microwave Studio frequency domain solver. First, simulations have been conduct in order to obtain the best trade-off between single cell’s parameters, varying iris aperture. Then, the both couplers, with and without pumping port, has been tuned to avoid reflections at the input port. Finally, the entire structure, with 5 cells, was simulated. The main structure parameters will be present and we will also show and discuss the acceleranting gradient obtained vary with linac lenght and input power

Progress on the π-mode X-band RF cavity for SPARC

The Frascati photo-injector SPARC (Pulsed Self Amplified Coherent Radiation Source) will be equipped with a X-band RF cavity for linearizing emittance to enhance bunch compression and for reducing bunch longitudinal energy spread. The nine cells standingwave cavity prototype made of separated cells has been already built and measured. In this paper we report on characterisation of the first brazed prototype. Heat load studies have been performed as well to design the cooling system for the final device

Progress on the hybrid gun project at UCLA

UCLA/INFN-LNF/Univ. Rome has been developing the hybrid gun which has an RF gun and a short linac for velocity bunching in one structure. After the cavity was manufactured at INFN-LNF in 2012, tests of the gun was carried out at UCLA. The field in the standing wave part was 20 % smaller than the simulation but the phase advance was fine. The cavity was commissioned successfully up to 13 MW. The beam test was performed at 11.5 MW and demonstrated the bunch compression

Electrical transport properties of microcrystalline silicon grown by PECVD

The dark conductivity and Hall mobility of hydrogenated silicon films deposited varying the silane concentration f=SiH4/(SiH4+H2) in a conventional plasma enhanced chemical vapor deposition system have been investigated as a function of temperature, taking into account their structural properties. The electrical properties have been studied in terms of a structural two-phase model. A clear transition from the electrical transport governed by a crystalline phase, in the range 1%3%, has been evidenced. Some metastable effects of the dark conductivity have been noticed

Structural and electrical properties of nanostructured silicon carbon films

Abstract The effect of the rf power on the structural and electrical properties of nanostructured silicon carbon films deposited by Plasma Enhanced Chemical Vapour Deposition system, using silane and methane gas mixture highly diluted in hydrogen, has been investigated. The structural and electrical properties are found to depend strongly on rf power. The increase of the rf power decreases the size of the silicon crystallites as well as the crystalline fraction and increases the carbon content in the films. The study not only indicates the correlation between crystalline fraction and the electrical conductivity but also reveals the presence of nanocrystallites in the films deposited at high rf power

Optical and electrical behavior of synthetic melanin thin films spray-coated

AbstractWe investigated the optical and the electrical conductivity properties of synthetic melanin thin films spray-coated on glass. These films showed a broadband monotonic increase of the absorption coefficient, decreasing the wavelength in the Visible-NIR range. Conductivity as a function of the temperature evidenced a semiconductor like character and a hysteretic behaviour after thermal annealing up to 475 K. Thermal activation energies extrapolated by resistance curves have been explained by using the framework of a band-model as for an amorphous semiconductor

RF Design and measurements of a C-Band prototype structure for an Ultra-High Dose-Rate medical linac

In this paper, we illustrate the RF design and measurements of a C-band prototype structure for an Ultra High Dose Rate medical linac. (1) Background: FLASH Radiotherapy (RT) is a revolutionary new technique for cancer cure. It releases ultra-high radiation dose rates (above 100 Gy/s) in microsecond short pulses. In order to obtain a high dose in a very short time, accelerators with high-intensity currents (the order of 100 mA peak currents) have to be developed. In this contest, Sapienza University, in collaboration with SIT-Sordina IORT Technology spa, is developing a new C-band linac to achieve the FLASH regime. (2) Methods: We performed the RF electromagnetic design of the prototype of the C band linac using CST STUDIO Suite Code and the RF low power RF test at Sapienza University of Rome. The measurements of the field in the cavity have been done with the bead-pull technique. (3) Results: This device is a nine-cell structure operating on the (Formula presented.) mode at 5.712 GHz (C-band). We report and discuss the test measurement results on a full-scale copper prototype, showing good agreement with CST RF simulations. A tuning procedure has been implemented in order to ensure proper operating frequency and to reach a field profile flatness of the order of a few percent. (4) Conclusions: The prototype of a C-band linac for FLASH applications was successfully tested with low RF power at Sapienza University. The fabrication and ad hoc tuning procedures have been optimized and discussed in the paper

Tuning procedure for traveling wave structures and its application to the C-Band cavities for SPARC photo injector energy upgrade

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Electromagnetic and beam dynamics studies for high gradient accelerators at terahertz frequencies

THz radiation is one of the most appealing portion of the electromagnetic spectrum in terms of multi-disciplinary use in basic science and technology. Beyond the numerous applications, a great interest is its potential for future, compact linear accelerators. Conventional radio-frequency accelerating structures operating at the S and C band can reach gradients up to 30 - 50MV/m, respectively; higher accelerating gradients, of the order of 100MV/m, have been obtained with X-band cavities. THz-based accelerating structures enable operation at even higher gradient, potentially up to the GV/m scale, holding great potential for their application to free-electron lasers and linear colliders, for instance. Here we present electromagnetic and beam dynamics studies about the use of a dielectric loaded waveguide to accelerate electron bunches by mean of a narrow-band multi-cycle THz pulse. The excitation of the accelerating structure by the THz pulse and the bunch acceleration in the excited field are investigated through CST Microwave Studio and GPT simulations

Compact S-band linear accelerator system for ultrafast, ultrahigh dose-rate radiotherapy

Radiation therapy is currently the most utilized technique for the treatment of tumors by means ofionizing radiation, such as electrons, protons and x/gamma rays, depending on the type, size and depth ofthe cancer mass. Radiation therapy has in general fulfilled the main requirement of targeting thus damagingthe malignant cells and sparing the healthy tissues as best as possible. In this scenario, electron linearaccelerators have been operated as viable tools for the delivery of both high-energetic electrons and x-raybeams, which are obtained via the bremsstrahlung process of the electrons hitting on a high-Z material.Recently, it has been experimentally demonstrated that ultrahigh dose-rate bursts of electrons and x-raybeams increase the differential response between healthy and tumor tissues. This beneficial response isreferred to as the FLASH effect. For this purpose, we have developed the first dedicated compactS-bandlinear accelerator for FLASH radiotherapy. This linac is optimized for a nominal energy of 7 MeV and apulsed electron beam current of 100 mA and above. The accelerator is mounted on a remote-controlledsystem for preclinical research studies in the FLASH regime. We will show the rf and beam dynamicsdesign of theS-band linac as well as the commissioning and high-power rf tests. Furthermore, the results ofthe dosimetric measurements will be illustrate