Search Results (11)

High-gradient accelerating radio frequency (RF) ] cavities are currently being developed in several national laboratories for applications in high-energy physics. Ultra-high accelerating gradients, reaching up to the GV/m range, can be achieved using ultra-compact accelerating structures operating in the sub-terahertz (sub-THz) regime. However, accurately measuring the key RF parameters of such compact structures presents significant experimental challenges, and even minor inaccuracies can lead to substantial errors. Additionally, RF simulations for these cavities often require extensive computational resources. Among the most critical parameters to determine is the reflection coefficient. To provide a fast and accurate analytical estimation, we have developed an electromagnetic theory describing the coupling between a resonant cavity and an RF waveguide. This approach is based on Bethe’s small-aperture polarization method, further developed by Collin. An exact analytical expression for the reflection coefficient is presented, formulated as a function of the physical parameters of the cavity waveguide system and applicable to arbitrary geometries, materials, and frequencies. Full article

This study investigates the magnetic fields produced by a three-solenoid system configuration using both traditional numerical solvers and fractional integral methods. We focus on the role of mesh resolution in influencing simulation accuracy, examining coils with dimensions 80 mm × 160 mm and a radius of 15.5 mm, each carrying a current of 200 A. Magnetic field behavior is analyzed along a line parallel to the central axis at a distance equal to half the solenoid’s radius. The fractional integral formulation employed provides a refined understanding of field variations, especially in off-axis regions. Comparisons with the Poisson solver highlight consistency across methods and suggest pathways for further optimization. The results support the potential of fractional approaches in advancing electromagnetic field modeling, particularly in accelerator and beamline applications. Full article

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 $\pi /2$ 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. Full article

Purpose: The electron linac ElectronFlash installed at Institut Curie (Orsay, France) is entirely dedicated to FLASH irradiation for radiobiological and pre-clinical studies. The system was designed to deliver an ultra-high-dose rate per pulse (UHDR) (above ${10}^6$ Gy/s) and a very high average dose rate at different energies and pulse durations. A campaign of tests and measurements was performed to obtain a full reliable characterizations of the electron beam and of the delivered dose, which are necessary to the radiobiological experiments. Methods: A Faraday cup was used to measure the electron charges in a single RF pulse. The percentage depth dose (PDD) and the transverse dose profiles, at the energies of 5 MeV and 7 MeV, were evaluated employing Gafchromic films EBT-XD for two Poly-methylmethacrylate (PMMA) applicators with irradiation sizes of 30 mm and 120 mm, normally used for in vivo and in vitro experiments, respectively. The results were compared with Monte Carlo (MC) simulations. Results: The measurements were performed during a period of a few months in which the experimental set up was adapted and tuned in order to characterize the electron beam parameters and the values of delivered doses before the radiobiological experiments. The measurements showed that the dose parameters, obtained at the energy of 5 MeV and 7 MeV with different applicators, fulfill the FLASH regime, with a maximum value of an average dose rate of 4750 Gy/s, a maximum dose per pulse of 19 Gy and an instantaneous dose rate up to 4.75 $\times {10}^6$ Gy/s. By means of the PMMA applicators, a very good flatness of the dose profiles was obtained at the cost of a reduced total current. The flatness of the large field is reliable and reproducible in radiobiological experiments. The measured PDD and dose profiles are in good agreement with Monte Carlo simulations with more than $95\%$ of the gamma-index under the thresholds of 3 mm/$3\%$. Conclusions: The results show that the system can provide UHDR pulses totally satisfying the FLASH requirements with very good performances in terms of beam profile flatness for any size of the fields. The monitoring of electron beams and the measurement of the dose parameters played an important role in the in vivo and in vitro irradiation experiments performed at the Institut Curie laboratory. Full article

Advanced technical solution for the design of a low perveance electron gun with a high quality beam dedicated to high power Ka-band klystrons is presented in this paper. The proposed electron gun can be used to feed linear accelerating structures at 36 GHz with an estimated input power of 20 MW, thus achieving an effective accelerating electric field in the (100–150) MV/m range. Additionally, in the framework of the Compact Light XLS project, a short Ka-band accelerating structure providing an integrated voltage of at least 15 MV, has been proposed for bunch-phase linearization. For the klystron, a very small beam dimension is needed and the presented electron gun responds to this requirement. An estimate of the rotational velocity at beam edge indicates that the diamagnetic field due to rotational currents are small compared to the longitudinal volume. A detailed analysis of how this has been achieved, including compression of the beam, rotation in the magnetic field, and analysis of the subsequently generated diamagnetic field has been discussed. Full article

In this work, we show the damage induced by an intense coherent terahertz (THz) beam on copper surfaces. The metallic surface was irradiated by multiple picosecond THz pulses generated by the Free Electron Laser (FEL) at the ISIR facility of the Osaka University, reaching an electric field on the sample surface up to ~4 GV/m. No damage occurs at normal incidence, while images and spectroscopic analysis of the surface point out a clear dependence of the damage on the incidence angle, the electric field intensity, and polarization of the pulsed THz radiation. Ab initio analysis shows that the damage at high incidence angles could be related to the increase of the absorbance, i.e., to the increase of the temperature around or above 1000 °C. The experimental approach we introduced with multiple fast irradiations represents a new powerful technique useful to test, in a reproducible way, the damage induced by an intense electric gradient on copper and other metallic surfaces in view of future THz-based compact particle accelerators. Full article

Large electric gradients are required for a variety of new applications, notably including the extreme high brightness electron sources for X-ray free electron lasers (FELs), radio-frequency (RF) photo-injectors, industrial and medical accelerators, and linear accelerators for particle physics colliders. In the framework of the INFN-LNF, SLAC (USA), KEK (Japan), UCLA (Los Angeles) collaboration, the Frascati National Laboratories (LNF) are involved in the modelling, development, and testing of RF structures devoted to particles acceleration by high gradient electric fields of particles through metal devices. In order to improve the maximum sustainable gradients in normal-conducting RF-accelerating structures, both the RF breakdown and dark current should be minimized. To this purpose, studying new materials as well as manufacturing techniques are mandatory to identify better solutions to such extremely requested applications. In this contribution, we discuss the possibility of using a dedicated coating on a solid copper sample (and other metals) with a relatively thick film to improve and optimize breakdown performances and to minimize the dark current. We present here the first characterization of MoO₃ films deposited on copper by pulsed-laser deposition (PLD). Full article

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. Full article

We present a conceptual design for a compact X-ray Source BriXS (Bright and compact X-ray Source). BriXS, the first stage of the Marix project, is an Inverse Compton Source (ICS) of X-ray based on superconducting cavities technology for the electron beam with energy recirculation and on a laser system in Fabry-Pérot cavity at a repetition rate of 100 MHz, producing 20–180 keV monochromatic X-Rays devoted mainly to medical applications. An energy recovery scheme based on a modified folded push-pull CW-SC twin Energy Recovery Linac (ERL) ensemble allows us to sustain an MW-class beam power with almost one hundred kW active power dissipation/consumption. Full article

Structural changes of MoO₃ thin films deposited on thick copper substrates upon annealing at different temperatures were investigated via ex situ X-Ray Absorption Spectroscopy (XAS). From the analysis of the X-ray Absorption Near-Edge Structure (XANES) pre-edge and Extended X-ray Absorption Fine Structure (EXAFS), we show the dynamics of the structural order and of the valence state. As-deposited films were mainly disordered, and ordering phenomena did not occur for annealing temperatures up to 300 °C. At ~350 °C, a dominant α-MoO₃ crystalline phase started to emerge, and XAS spectra ruled out the formation of a molybdenum dioxide phase. A further increase of the annealing temperature to ~500 °C resulted in a complex phase transformation with a concurrent reduction of Mo⁶⁺ ions to Mo⁴⁺. These original results suggest the possibility of using MoO₃ as a hard, protective, transparent, and conductive material in different technologies, such as accelerating copper-based devices, to reduce damage at high gradients. Full article