• R. Pakter, L.C. Martins, F.B. Rizzato
  IF-UFRGS, Porto Alegre

Funding: Work supported by CNPq, Brazil and the US-AFOSR under Grant No. FA9550-06-1-0345.

In this paper, we investigate the combined envelope-centroid dynamics of relativistic continuous charged beams transported through a uniform focusing field and surrounded by a conducting wall. For such beams, the conducting wall screens the electric field but allows magnetic field penetration, enhancing the induced charges effect on the beam transport. As a consequence, in contrast to the case of nonrelativistic beams where the walls are shown to have little effect*, relativistic beams may have their centroid motion severely affected, leading to limitations in the total current and area occupied by the beam inside the conductor. Self-consisted simulation are used to verify the findings.

*K. Fiuza, F. B. Rizzato, and R. Pakter, Phys. Plasmas, 13, 023101 (2006).

• F.B. Rizzato, A. Endler, R.P. Nunes, R. Pakter, E.G. Souza
  IF-UFRGS, Porto Alegre

Funding: CNPq, Brazil; AFOSR FA9550-06-1-0345, USA

In this work we analyze the dynamics of mismatched inhomogeneous beams of charged particles. Initial inhomogeneities lead to propagating density waves across the beam core, and the presence of density waves eventually results in density build up and particle scattering. Particle scattering off waves in the beam core and the presence of resonances due to envelope mismatches ultimately generate a halo of particles with concomitant emittance growth. Emittance growth directly indicates when the beam relaxes to its final stationary state, and the purpose of the present paper is to describe halo and emittance in terms of test particles moving under the action of the mismatched inhomogeneous beam. To this end we develop an average Lagrangian approach for the beam where both density and envelope mismatches are incorporated. Test particle results compare well with full simulations.

• A. Bonatto, R. Pakter, F.B. Rizzato
  IF-UFRGS, Porto Alegre

Funding: This work has received financial support from AFOSR, Arlington, VA (under Grant FA9550-06-1-0345) and from CNPq, Brazil.

In the present analysis we study the self consistent propagation of intense laser pulses in a cold relativistic ideal-fluid underdense plasma, with particular interest in how the envelope dynamics is affected by the plasma frequency. Analysis of the linear system associated with the chosen model shows the existence of thresholds that can led propagating pulses to distinct modulational instabilities, according to the relation between its transversal wave vector and the plasma frequency.