IF-UFRGS, Porto Alegre
A theoretical framework that allows to accurately calculate the distribution functions and the emittance growth of an initially mismatched charged-particle beam after it relaxes to equilibrium is presented. The theory can be used to obtain the fraction of particles which will evaporate from the beam to form the halo. It is applied both to highly space charge dominated beams*, as well as to beams with finite initial emittance** with general initial distributions***. Results based on an approximation of the theory that allows simpler analytic expressions for the final stationary state are also presented. The calculated emittance growth and final beam distribution are found to be in good agreement with N-particle beam simulations.
* Nunes, Pakter, Rizzato, Phys. Plasmas 14, 023104 (2007).
** Levin, Pakter, Teles, Phys. Rev. Lett. 100, 040604 (2008).
*** Teles, Pakter, Levin, Appl. Phys. Lett. 95, 173501 (2009).
IF-UFRGS, Porto Alegre
UFPel, Pelotas
In this paper, the dynamics of inhomogeneous high-intensity charged particles beams is investigated. While for homogeneous beams the whole system oscillates with a single frequency, any inhomogeneity leads to propagating transverse density waves which eventually result in a singular density build up, causing wave breaking and jet formation*. A theory is presented which allows to analytically calculate the time at which the wave breaking takes place. It also gives a good estimate of the time necessary for the beam to relax into the final stationary state consisting of a cold core surrounded by a halo of highly energetic particles. The halo size and emittance growth are estimated using a core-particle type analysis where the inhomogeneous core density evolution is determined based on an average Lagrangian approach**. The role of envelope mismatches in the wave breaking process is also studied. The analysis reveals that the wave breaking time is very susceptible to the mismatch; judiciously chosen mismatches can largely extend beam lifetimes***.
*Anderson, Rosenzweig, PRST AB 3, 094201 (2000); Rizzato, Pakter, Levin, Phys Plas 14, 110701 (2007).
**Nunes, Pakter, etal, Phys Plas 16, 033107 (2009).
***Souza, etal , APL 96, 141503 (2010).
