Design of a plasma discharge circuit for particle wakefield acceleration

Abstract

a b s t r a c tPlasma wakefield acceleration is the most promising acceleration technique known nowadays, able to provide very high accelerating fields (10-100 GV m À 1 ), enabling acceleration of electrons to GeV energy in few centimetres. However, the quality of the electron bunches accelerated with this technique is still not comparable with that of conventional accelerators; radiofrequency-based accelerators, in fact, are limited in the accelerating field (10-100 MV m À 1 ) requiring therefore kilometric distances to reach the GeV energies, but can provide very bright electron bunches. Combining high brightness electron bunches from conventional accelerators and high accelerating fields reachable with plasmas could be a good compromise allowing to further accelerate high brightness electron bunches coming from LINAC while preserving electron beam quality. Following the idea of plasma wave resonant excitation driven by a train of short bunches, we have started to study the requirements in terms of plasma for SPARC-LAB [1,2]. In particular, here we focus on the ionization process; we show a simplified model to study the evolution of plasma induced by discharge, very useful to design the discharge circuit able to fully ionize the gas and bring the plasma at the needed temperature and density.

Modeling and diagnostics for plasma discharge capillaries

“…In gases, in fact, there is always a very low percentage of free electrons, due to natural reasons such as heat exchange with the environment and environmental radiation. The resistivity of a gas evolving into a plasma can be written as [15,16] ρ tot = ρ ei + ρ ae = m e n e e 2 (ν ei + ν ae ),…”

“…Our description is not able to give local values of the plasma current density, of the associated magnetic field [14], and of the plasma density, but it can efficiently take into account the plasma heating, the heating of the capillary walls, i.e., the heat flux moving from the plasma to the walls of its container, and finally all the radiative losses due to bremsstrahlung radiation (BR) and the radiative recombination (RR). In this sense, the presented macroscopic model consists in an improvement of a preexisting one [15,16], where many of these physical mechanisms were not included. Jointly, we propose an analytic model for the study of plasma discharge capillaries at thermal equilibrium, stressing the relevance of the radiation losses to the transverse profile of the plasma temperature and all the related quantities.…”