Microwave accelerating structures: an innovative parallel coupled electron LINAC

Particle accelerators are employed in many fields of the physics, engineering and medicine science. Although the idea of acceleration of charged particles by means of time varying electromagnetic field is an almost century old, the research and development in this field is active more than ever. An efficient particle accelerator gives the opportunity to reach energy levels not yet achieved and allows the study of the deepest laws of the physics. Also a better performance of the particle accelerators is desirable in order to develop compact table-top machine for medical or industrial purpose. The work here presented takes place in this framework. A parallel coupled electron LINAC has been studied for high gradient operation in the X-band frequency. This kind of device can address some issues of high gradient accelerating LINAC. Due to decoupled propagation axes for RF power and beam it is possible to increase the structure shunt impedance without affecting the cell to cell coupling, combining the advantages of travelling and standing wave structures. Besides in case of a breakdown only the energy stored in one cell is involved in the discharge process and not the total energy stored of the section, thus the damages caused by the breakdown event are expected to be smaller. Following a discussion on how the proposed configuration was conceived, full wave simulations were carried out to numerically validate the idea and to optimize the single cell in order to minimize the probability of breakdowns. After a successful cold simulation a beam dynamics analysis has been done in order to estimate the properties of the beam moving inside the device. Due to the small irises dimension the transverse wakefield can be source of instability for the bunch propagation. Therefore this issue has been investigated by means of numerical methods. Finally, the problem of the beam alignment with respect to the accelerating section is addressed and the results of a device suitable to beam position measurement are presented.