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We present the conceptual design of a compact light source named BriXSinO. BriXSinO was born as demonstrator of the Marix project, but it is also a dual high flux radiation source Inverse Compton Source (ICS) of X-ray and Free-Electron Laser of THz spectral range radiation conceived for medical applications and general applied research. The accelerator is a push-pull CW-SC Energy Recovery Linac (ERL) based on superconducting cavities technology and allows to sustain MW-class beam power with almost just one hundred kW active power dissipation/consumption. ICS line produces 33 keV monochromatic X-Rays via Compton scattering of the electron beam with a laser system in Fabry-Pérot cavity at a repetition rate of 100 MHz. The THz FEL oscillator is based on an undulator imbedded in optical cavity and generates THz wavelengths from 15 to 50 micron., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

High order modes (HOMs) in multi-cell superconducting cavities are of particular concern in beam dynamics of linear accelerators, mainly those operating in CW mode with high current and high repetition rate. These undesired modes may invoke beam instabilities, beam breakup and increase the energy spread if not correctly pulled out and damped. The study reported in this paper is applied for damping the HOMs in the main Linac of BriXSinO, an ongoing project of an Energy Recovery Linac at LASA INFN laboratory. We developed a numerical model to study the interaction of monopole HOMs with the beam in long timescale. The presented model, named HOMEN (High Order Modes Evolution based on eNergy budget), allows the evaluation of the loss factor Kloss, crucial for evaluating the perturbing modes. At the same time, electromagnetic simulations of the standing wave multicell cavity, highlighted the dangerous modes and revealed a tolerable beam energy spread induced by HOMs. This method allows us to distinguish all dangerous modes of our interest for implementing the necessary damping mechanisms., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

The Damping Rings (DRs) complex of the Compact LInear Collider (CLIC) has to provide ultra low emittances to the linear accelerating sections in order to reach a luminosity of $2\times10^{34}$ cm$^2$ s$^{-1}$ at the centre of mass energy $3$ TeV. Due to the high intensity, short bunches and low transverse emittances, collective effects are expected to seriously affect the performance of the DRs, limiting the electron and positron beam intensity at extraction, or causing an intolerable degradation of the beam quality. The design of the machine has to be optimized already at a very early stage in order to ensure that all the instability thresholds stay above the operational target intensities with sufficient safety margin. To this end, the impedance model of the DRs is developed and used for studying instability thresholds with the PyHEADTAIL code. Starting from a simplified model of the whole machine, the code allows to take into account the radiation damping and quantum excitation effects due to the synchrotron radiation emission and also the resistive wall contribution. The knowledge of the surface impedance up to hundreds of GHz, to which the bunch spectrum extends, is essential for the correct resistive wall impedance modeling of the coatings deposited on the vacuum chambers of the machine. Specifically, Non Evaporable Getter (NEG) is a commonly used coating to allow a distributed and continuous pumping in vacuum chambers and the amorphous Carbon (a-C) is deposited in order to avoid the onset of the Electron Cloud (EC) in the accelerator vacuum chamber. The core of this thesis consists in the development of a reliable, handy, and inexpensive measurement system for the Electromagnetic Characterization (EMC), in the sub-THz frequency range, of coating materials. The method is based on time domain measurements of an electromagnetic wave passing through a Device Under Test (DUT) made of a waveguide with a thin central slab, where the coating material is deposited on both sides. This device has two main advantages: the deposition homogeneity with predictable thickness and the possibility to reuse the system for further measurements on different coating materials. The assessment of the signal attenuation through the DUT is analytically evaluated and confirmed with numerical simulations. This novel technique is tested on slabs coated with NEG and allows the electromagnetic characterization and the surface impedance evaluation up to hundreds of GHz.

The LHC collimation system is a critical element for the safe operation of the LHC machine and is subject to continuous performance monitoring, hardware upgrade and optimization. In this work we will address the impact on impedance of the upgrades performed on the TDI injection protection collimator, where the absorber material has been changed to mitigate the device heating observed in machine operation, and on selected secondary (TCS) and tertiary (TCT) collimators, where beam position monitors (BPM) have been embedded for faster jaw alignment. Concerning the TDI, we will present the RF measurements performed before and after the upgrade, comparing the result to heating and tune shift beam measurements. For the TCTs, we will study how the higher order modes (HOM) introduced by the BPM addition have been cured by means of ferrite placement in the device. The impedance mitigation campaign has been supported by RF measurements whose results are in good agreement with GdfidL and CST simulations. The presence of undamped low frequency modes is proved not to be detrimental to the safe LHC operation., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

The presentation will cover approaches and strategies of modeling and implementing collective effects in modern simulation codes. We will review some of the general approaches to numerically model collective beam dynamics in circular accelerators. We will then look into modern ways of implementing collective effects with a focus on plainness, modularity and flexibility, using the example of the PyHEADTAIL framework, and highlight some of the advantages and drawbacks emerging from this method. To ameliorate one of the main drawbacks, namely a potential loss of performance compared to the classical fully compiled codes, several options for speed improvements will be mentioned and discussed. Finally some examples and application will be shown together with future plans and perspectives., Proceedings of the 57th ICFA Advanced Beam Dynamics Workshop on High-Intensity and High-Brightness Hadron Beams, HB2016, Malmö, Sweden

One of the most significant technological problems to achieve the nominal performances in the Large Hadron Collider (LHC) concerns the system of collimation of particle beams. The use of collimators crystals, exploiting the channeling effect on extracted beam, has been experimentally demonstrated. The first part of this thesis is about the optimization of UA9 goniometer at CERN, this device used for beam collimation will replace a part of the vacuum chamber. The optimization process, however, requires the calculation of the coupling impedance between the circulating beam and this structure in order to define the threshold of admissible intensity to do not trigger instability processes. Simulations have been performed with electromagnetic codes to evaluate the coupling impedance and to assess the beam-structure interaction. The results clearly showed that the most concerned resonance frequencies are due solely to the open cavity to the compartment of the motors and position sensors considering the crystal in operational position. The numerical modeling is complicated for not-elementary geometry structures, especially when the materials inside the structure have unknown or complex electromagnetic properties. The second part of the thesis illustrates a numerical/experimental methodology benchmark to evaluate the coupling impedance also for complicated structures. A canonical pillbox has been characterized for the validation of this methodology. A comparison among analytical formulas, numerical results and experimental measurements has been performed. The results are encouraging and also applicable to different geometries.

The UA9 piezo-goniometer has been designed to guarantee micro-radians-accuracy angular positioning of a silicon crystal for a crystal collimation experiment in the LHC, and to minimize the impact on the LHC beam-coupling impedance. This paper presents a Finite Element Method (FEM) study of the device, in both parking and operational positions, to evaluate its impact on the LHC impedance budget. The study has been a progressive simulation work, started from the simplification of the original detailed design, and aimed at highlighting the effect of single details (e.g. objects in confining chambers) on the longitudinal and transverse components of beam-coupling impedance. In addition, the shielding contribution of the RF gaskets has been carefully evaluated, with the objective to assess the consequences for operation in case of their failure. Sensitivity analyses to simulation parameters are also performed, in order to test the FEM model robustness. A final word is drawn on the overall device impedance criticality., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

Resistive-wall impedance constitutes a significant percentage of the total beam-coupling impedance budget of an accelerator. A number of different reduction techniques have been proposed during the years depending on the specific applications, ranging from higher order modes damping to solutions entailing high electrical-conductivity coatings of the pipe. This article investigates the use of metamaterial-based absorbers for sensibly reducing or nearly canceling the beam-coupling impedance. We design and fabricate subwavelength 2-D metallic resonant structures based on the split-ring resonator (SRR) geometry that can be employed as mode dampers in accelerating structures. A number of prototypes have been fabricated and measured in a “test model” pillbox cavity. Experimental results, combined with full-wave electromagnetic simulations, prove the efficiency of the SRR-based metamaterials. This article opens up to the possibility of considering metamaterials as a valid alternative to other devices for impedance mitigation in experimental setups commonly operating along a particle beamline, such as accelerating cavities or collimators, and more in general for the development of filters with a large out-of-band signal rejection in specific applications.