Roger Pizzato Nunes

Simplified self-consistent model for emittance growth in charged beams with mismatched envelopes

This paper analyzes the envelope dynamics of magnetically focused, high-intensity charged particle beams. As known, mismatched envelopes decay into equilibrium with simultaneous emittance growth. To describe the emittance growth we develop a simplified self-consistent macroscopic model: emittance is evaluated in a partially analytical way which invokes the beam profile, with self-consistency resulting from the inclusion of the emittance growth into the envelope equation. The model is then compared with full N-particle beam simulations and the agreement is shown to be quite reasonable. The model helps to understand the physics of the problem and is computationally faster than full simulations. Other aspects are discussed in the paper.

An analytical model to determine equilibrium quantities of azimuthally symmetric and mismatched charged particle beams under linear focusing

The model developed here analytically allows to obtain equilibrium quantities of interest from high-intensity charged particle beams such as the emittance, beam envelope, and the number of beam halo particles. The results obtained in this work have been particularized to the case of initially homogeneous beams, with azimuthal symmetry, and focused by a constant magnetic field while confined in a linear channel. For validation, full self-consistent N-particle beam simulations have been carried out and its results compared with the predictions supplied by the developed hybrid numerical-analytical model. The agreement has been reasonable. Also, the model revealed to be useful to understand the basic physical aspects of the problem.

Relaxation of intense inhomogeneous charged beams

This work analyzes the dynamics of inhomogeneous, magnetically focused high intensity beams of charged particles. Initial inhomogeneities lead to density waves propagating transversely in the beam core, and the presence of transverse waves eventually results in particle scattering. Particle scattering off waves in the beam core ultimately generates a halo of particles with concomitant emittance growth. Emittance growth indicates a beam relaxing 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 inhomogeneous beam. To this end an average Lagrangian approach for the beam is developed. This approach, aided by the use of conserved quantities, produces results in nice agreement with those obtained with full N-particle numerical simulations.

A comparison of experimental results of soot production in laminar premixed flames

Abstract Soot emission has been the focus of numerous studies due to the numerous applications in industry, as well as the harmful effects caused to the environment. Thus, the purpose of this work is to analyze the soot formation in a flat flame burner using premixed compressed natural gas and air, where these quasi-adiabatic flames have one-dimensional characteristics. The measurements were performed applying the light extinction technique. The air/fuel equivalence ratiowas varied to assess the soot volume fractions for different flame configurations. Soot production along the flamewas also analyzed by measurements at different heights in relation to the burner surface. Results indicate that soot volume fraction increases with the equivalence ratio. The higher regions of the flamewere analyzed in order to map the soot distribution on these flames. The results are incorporated into the experimental database for measurement techniques calibration and for computational models validation of soot formation in methane premixed laminar flames, where the equivalence ratio ranging from 1.5 up to 8.

Nonlinear dynamics of inhomogeneous mismatched charged particle beams

This work analyzes the transversal dynamics of an inhomogeneous and mismatched charged particle beam. The beam is azimuthally symmetric, initially cold, and evolves in a linear channel permeated by an external constant magnetic field. Based on a Lagrangian approach, a low-dimensional model for the description of the beam dynamics has been obtained. The small set of nonlinear dynamical equations provided results that are in reasonable agreement with that ones observed in full self-consistent N-particle beam numerical simulations.

Nonlinear dynamics of relativistic charged particle beams

The idea behind this work is to analyze the transversal dynamics of a relativistic charged particle beam. The beam is azimuthally symmetric, focused by a constant magnetic field and supposed to be initially cold. While mismatched, nonrelativistic, and homogeneous beams oscillate with an invariant cold density profile, it is shown that relativistic homogeneous beams progressively heat and lose an important amount of constituents during its magnetic confinement. This heating process starts with phase-space wave-breaking, a mechanism observed before in initially inhomogeneous beams. The results have been obtained with full self-consistent N-particle beam numerical simulations.

Analytical method for determining at equilibrium the envelope and emittance of initially mismatched beams

This work presents a fully analytic way of determining relevant equilib- rium quantities of a high-intensity charged particle beam submitted to magnetic focusing while inside a linear channel. Through the current approach, some inter- mediate steps of our original hybrid model which had to be solved numerically can now be eliminated, leading to the obtainment of a fully analytic expression. This expression relates the initial beam parameters with those at equilibrium, allow- ing beam macroscopic quantities such as envelope and emittance to be naturally and analytically determined. For validation, full self-consistent N -particle beam numerical simulations have been carried out and the results compared with the predictions supplied by the full analytical model. The agreement is shown to be good with the simulations and also with the original hybrid numerical-analytical version of the model.

Transversal dynamics of relativistic charged particle beams

The idea behind this work is to analyse the transversal dynamics of a relativistic charged particle beam. The beam is azimuthally symmetric, focused by a constant magnetic field and supposed initially cold. While mismatched, nonrelativistic and homogeneous beams oscillate with an invariant cold density profile, it is shown that relativistic homogeneous beams progressively heat and lose an important amount of constituents during its magnetic confinement. This heating process starts with phase-space wave breaking, a mechanism observed before in initially inhomogeneous beams. The results have been obtained with full self-consistent N -particle beam numerical simulations.

The initial inhomogeneity and halo formation in intense charged particle beams

Although undesired in many applications, the intrinsic and spurious spatial inhomogeneity that permeates real systems is the forerunner instability that leads high-intensity charged particle beams to its equilibrium. In general, this equilibrium is reached in a particular way, by the development of a tenuous particle population around the original beam, conventionally known as the halo. In this direction, the purpose of this work is to analyze the influence of the magnitude of the initial inhomogeneity over the dynamics of quasi-homogeneous mismatched beams. For that, all beam constituent particles, which are initially disposed in an equidistant form, suffer a progressive perturbation through a noise of a variable amplitude. Beam quantities are quantified as functions of the noise amplitude, which indirectly is assumed a consistent measure of the initial beam inhomogeneity. The results have been obtained by the means of full self-consistent N-particle beam numerical simulations and seem to be an important complement to the investigations already carried out in prior works.

Wave breaking and particle jets in inhomogeneous beams

We analyze the dynamics of inhomogeneous, magnetically focused high-intensity beams of charged particles. 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. The theory presented in this paper 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.