An Efficient Computation of Coherent Synchrotron Radiation in a Rectangular Chamber, Applied to Resistive Wall Heating

We study coherent synchrotron radiation (CSR) in a perfectly conducting vacuum chamber of rectangular cross section, in a formalism allowing an arbitrary sequence of bends and straight sections. We apply the paraxial method in the frequency domain, with a Fourier development in the vertical coordinate but with no other mode expansions. A line charge source is handled numerically by a new method that rids the equations of singularities through a change of dependent variable. The resulting algorithm is fast compared to earlier methods, works for short bunches with complicated structure, and yields all six field components at any space-time point. As an example we compute the tangential magnetic field at the walls. From that one can make a perturbative treatment of the Poynting flux to estimate the energy deposited in resistive walls. The calculation was motivated by a design issue for LCLS-II, the question of how much wall heating from CSR occurs in the last bend of a bunch compressor and the following straight section. Working with a realistic longitudinal bunch form of r.m.s. length $10.4~\mu$m and a charge of 100 pC we conclude that the radiated power is quite small (28 W at a 1 MHz repetition rate), and all radiated energy is absorbed in the walls within 7 m along the straight section.Comment: 47 pages, 24 figure

La collaborazione tra consumatori e imprese nel passaparola on line. Analisi teorica ed empirica della comunita Zzub.it.

La tesi consiste in un approfondimento sul passaparola online (Word of Mouth, WOM) con particolare riferimento alla collaborazione in questo campo tra consumatori e aziende. Nello specifico si analizza il caso della comunità online del passaparola ZZUB.it, sia da un punto di vista teorico, sia empirico. I capitoli iniziali riguardano la teoria legata al passaparola (evoluzione negli studi, dove si misura, perché i consumatori fanno passaparola, Le aziende del passaparola, le problematiche) e alle virtual communities (definizioni, Corporate Community, Consumer community). Segue, la parte empirica sull’impresa case study, con particolare riferimento al suo funzionamento, al profilo degli utenti che ne fanno parte e al tipo di communit

Studies of Coherent Synchrotron Radiation with the Discontinuous Galerkin Method

In this thesis, we present methods for integrating Maxwell\u27s equations in Frenet-Serret coordinates in several settings using discontinuous Galerkin (DG) finite element method codes in 1D, 2D, and 3D. We apply these routines to the study of coherent synchrotron radiation, an important topic in accelerator physics. We build upon the published computational work of T. Agoh and D. Zhou in solving Maxwell\u27s equations in the frequency-domain using a paraxial approximation which reduces Maxwell\u27s equations to a Schrödinger-like system. We also evolve Maxwell\u27s equations in the time-domain using a Fourier series decomposition with 2D DG motivated by an experiment performed at the Canadian Light Source. A comparison between theory and experiment has been published (Phys. Rev. Lett. 114, 204801 (2015)). Lastly, we devise a novel approach to integrating Maxwell\u27s equations with 3D DG using a Galilean transformation and demonstrate proof-of-concept. In the above studies, we examine the accuracy, efficiency, and convergence of DG