1,721,127 research outputs found
Design realization and commissioning of RF Power system and accelerating structures for a Gamma Source
Full text linkThanks to the recent technological progress in the fields of high power lasers and high brightness linac accelerators, new Gamma and X ray sources based on electron-photon interaction are under development in several laboratory world-wide. These kind of sources uses Inverse Compton scattering in the collision between a relativistic high quality electron beam and high power optical laser pulses to generate secondary photon beams of unique performances. These photon beams are suitable for a wide range of applications and open new perspectives in many research fields. In particular gamma rays in the energy interval between 1-20~MeV are of great interest for basic research and application studies in the fields of nuclear physics and photonics. In this framework, a very innovative Compton source is under construction in Magurele (RO), by the EuroGammaS association, with the aim to generate photon beams in that energy range, characterized by unprecedented performances in terms of mono-chromaticity, brilliance, spectral density, tunability and polarization. The realization of this source called ELI-NP-GBS is in the framework of the European Extreme Light infrastructure (ELI) project that pursues the creation of an international laser research infrastructure. The challenging parameters of this source rely on the performances of the Linac and in particular of his radiofrequency (RF) system. The electron accelerator is a high brightness normal conducting RF Linac consisting of two S-band (2856 MHz) and twelve C-band (5712 MHz) RF structures. The main advantages of using a Linac accelerator are the energy "tunability" and the excellent electron beam quality that is possible to obtain. The accelerator will be operated at a repetition rate of 100 Hz. For every RF pulse up to 32 electron bunches, each one carrying 250 pC of charge, separated by 16 ns, will be accelerated. The Linac is required to achieve a normalized emittance in both planes better than 0.5 mm mrad and energy spread below 0.1\%. To guarantee these performances in a reliable and stable way, innovative and advance RF components have been developed. The aim of this thesis is the study, design and commissioning of the main components of RF system used for the realization of a state of the art gamma source such as the ELI-NP-GBS. High power RF sources driven by solid state modulators have to feed the accelerating structures with high pulse to pulse amplitude stability and RF pulse uniformity in order to minimize the electron beam energy spread. An innovative C-band High Order Mode (HOM) damped RF cavity has been conceived and designed in order to avoid beam emittance and energy spread degradation due to the Beam Break-Up instability along the Linac. In addition the S-band RF Gun has been realized with an innovative technique called "Gasket-clamping technique'' and implements new radiofrequency features to sustain the 100 Hz repetition rate operation. All these devices have been realized and tested and the results obtained are reported in this work. Taking into account the extremely good results obtained by RF Gun realized with the gasket-clamping technique, in the last part of this dissertation, it has been explored the possibility to extend this fabrication procedure to the realization of an entire travelling wave Linac structure. This technique, thanks to the use of RF/vacuum special gaskets, allows avoiding the brazing process thus reducing the fabrication costs, the risk of failure and improving the performances of the device in terms of reachable peak electric field. To demonstrate the feasibility of the implementation of such technique an accurate electromagnetic and mechanical design of an S-band travelling wave structure has been performed
Design and measurements of the high gradient accelerating structures
Full text linkThe purpose of this thesis was to study on design and measurements of the high gradient accelerating structures. After introducing the main parameters to characterize Linacs we explained the application of the periodic accelerating structure. Then we studied TW accelerating structure operating at K-band frequency in order to linearize longitudinal space phase to increase beam brightness in the framework of the Compact Light XLS project in order to produce hard x-ray. We estimated group velocity as a function of frequency both analytically and numerically. Analytical results have a good agreement with the numerical results. The main parameters such as shunt impedance, quality factor (Geometric factor) and R/Q independently from the operating frequency for the TM010, TM110 and TM011 for a single cylindrical “pill-box” have been determined analytically as they provide accurate model for the accelerating structures.
In order to characterize a normal conducting high accelerating structure with maximum gradients operating at X-band with extremely low probability of RF breakdown, an electroformed SW structures has been fabricated and characterized by SLAC and INFN with collaboration of other institute around the world at 11.424 GHz, coated with Au-Ni. We designed a gold plate RF high gradient structure operating at the X- band coated with Au-Ni. Bench measurements have been performed in the Department of SBAI of the University of Rome “La Sapienza”. The Slater method for the SW cavity has been employed in order to quantify the electric field inside the structure. Comparing the results with the results exposed from HFSS we report the features that have been quantified, showing good agreement. We continued working on the perturbation effect due to the aperture coupled between a waveguide and a cavity but for our application in SW multi-cell high gradient accelerating structure we studied on theoretical approach for reflection coefficient calculation in a SW cavity coupled to a waveguide. One method was based on circuit theory in which we found the overall Q of a resonant circuit for a cavity coupled to an external waveguide containing the RF generator. Q calculation led to the determining of the shunt impedance and consequently the reflection coefficient calculation. Comparison of the results shows a good agreement with the numerical results carried out by using the numerical code, HFSS. Another method of reflection coefficient calculation has been accomplished. We applied the modified Bethe’s theory presented by Collin and developed by De santis, Mostacci and L.Palumbo for TM01 mode cavities coupled by a small hole with a thickness size comparable to the wavelength. The amplitudes of forward and backward waves due to polarizabilites have been determined and we found equations for reflection and transmission coefficients. We demonstrated that our equation for reflection coefficient calculation is an analogous of the reflection coefficient obtained by Collin for TE10 using the circuit theory
Longitudinal beam dynamics simulation in electron rings in strong rf focusing regime
No full textObtaining very short bunches in an electron storage ring is one of the frontiers of the accelerator physics. The strong rf focusing (SRFF) is a way to have short bunches at a given position in the ring, thanks to the principle of the bunch length modulation. Until now, the bunch length modulation has been studied only in the limit of zero current; in this paper we present the results of a simulation code suitable to study the effects of coherent synchrotron radiation and vacuum chamber wakefields on the single bunch longitudinal dynamics in the SRFF regime. The code has been applied to three different lattices that can be realized in the Frascati e(+)/e(-) collider DA Phi NE for a possible experiment on bunch length modulation
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