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

Plasmonic lenses for tunable ultrafast electron emitters at the nanoscale

Simultaneous spatiotemporal confinement of energetic electron pulses to femtosecond and nanometer scales is a topic of great interest in the scientific community, given the potential impact of such developments across a wide spectrum of scientific and industrial applications. For example, in ultrafast electron scattering, nanoscale probes would enable accurate maps of structural dynamics in materials with nanoscale heterogeneity, thereby leading to an understanding of the role of boundaries and defects on macroscopic properties. On the other hand, advances in this field are mostly limited by the brightness and size of the electron source. We present the design, fabrication, and optical characterization of bullseye plasmonic lenses for next-generation ultrafast electron sources. Using electromagnetic simulations, we examine how the interplay between light-plasmon coupling, plasmon propagation, dispersion, and resonance governs the properties of the photoemitted electron pulse. We also illustrate how the pulse duration and strength can be tuned by geometric design and predict that sub-10-fs pulses with nanoscale diameter can be achieved. We then fabricate lenses in gold films and characterize their plasmonic properties using cathodoluminescence spectromicroscopy, demonstrating suitable plasmonic behavior for ultrafast nanoscale photoemission

Impedance measurements and simulations on the TCT and TDI LHC collimators

The LHC collimation system is a critical element for the safe operation of the LHC machine and it 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 injection protection target dump (TDI), 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. Con- cerning the TDI, we will present the RF measurements per- formed 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) intro- duced 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 simula- tions. The presence of undamped low frequency modes is proved not to be detrimental to the safe LHC operation

Coherence properties and diagnostics of betatron radiation emitted by an externally-injected electron beam propagating in a plasma channel

A 3-dimensional time-domain simulation of X-ray produced by a laser wakefield accelerated electron beam was performed in order to know its properties like intensity, spectrum, divergence and coherence. Particular attention was paid to the coherence around the acceleration axis. The broad spectrum of betatron radiation (1–10 keV) leads to a short coherence length. Nevertheless we observe that under particular detection condition the spatial coherence has a characteristic enlargement. We give a simplified interpretation of this effect in terms of phase shift of the electric field on a virtual detector. Moreover we describe a near field scattering technique to characterize the betatron radiation. This diagnostics will be used to map the transverse spatio-temporal coherence of X-ray radiation in the laser wakefield accelerator under development at Frascati National Laboratories (LNF)

On trapped modes in the LHC recombination chambers: numerical and experimental results

The recombination chamber in LHC (Large Hadron Collider) allows the separated proton beams to merge into a common vacuum chamber surrounding the interaction points. It has been subject of thorough studies concerning its interaction with the circulating beam. In this paper we present the numerical and experimental results of our investigation. We show that in the smooth transitions between pipes of different diameters a trapped mode may exist. The mode results to be not harmful for the LHC operation, both for the beam stability and power loss

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