We determine the second-order correction to the gain function of the microbunching instability in single-pass systems of interest for the next generation of light sources. The calculation applies to the case where the instability is seeded by shot noise. We examine an analytically treatable model of beam dynamics where collective forces are active only in non-dispersive sections of the linac. We find that the second order term can augment the linear gain significantly while affecting the spectrum of the overall gain only marginally. The weight of the second-order correction relative to the linear gain is found to scale quadratically with respect to R56. The qualitative behavior predicted by the model is consistent with exact numerical solutions of the Vlasov equations for realistic lattices.

# Your search: "author:"Venturini, Marco""

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## Scholarly Works (32 results)

We simulate electron cloud build-up in a grooved vacuum chamber including the effect of space charge from the electrons. We identify conditions for e-cloud suppression and make contact with previous estimates of an effective secondary electron yield for grooved surfaces.

Characterization of single-bunch instabilities in the International Linear Collider (ILC) damping rings (DRs) has been indicated as a high-priority activity toward completion of an engineering design. In this paper we report on a first estimate of the current thresholds for the instability using numerical and analytical models of the wake potentials associated with the various machine components. The numerical models were derived (upon appropriate scaling) from designs of the corresponding components installed in existing machines. The current thresholds for instabilities were determined by numerical solution of the Vlasov equation for the longitudinal dynamics. For the DR baseline lattice as of Feb. 2007 we find the critical current for instability to be safely above the design specifications leaving room for further optimization of the choice of the momentum compaction.

Space-charge effects in the low-energy ring of the proposed Super-B Factory are studied using a weak-strong model of dynamics as implemented in the code Marylie/Impact (MLI). The impact of space charge appears noticeable but our results suggest the existence of workable regions of the tune space where the design emittance is minimally affected. However, additional studies are recommended to fully substantiate this conclusion.

Using first-order perturbation theory for maps, we extend the familiar formulae for space-charge tuneshift to encompass the case of a fully coupled lattice.

Use of a one-dimensional model of longitudinal space-charge (SC) impedance has been proposed for studying the microbunching instability in single-pass delivery systems relevant for the next generation of FELs. For beams with uniform transverse density and circular cross-section of radius r_b the SC impedance can be expressed in a handy analytical form, making this model particularly convenient. In this report we show how with an appropriate choice of r_b one can use this as an effective-beam model to approximate beams with non-axis symmetric and non-uniform transverse densities.

We apply a recently developed Vlasov solver to the study of themicrobunching instability generated by shot noise in the beamdelivery systems of x-ray Free Electron Lasers (FELs). We discusstwo lattices presently under consideration for the FEL FERMI project at Elettra and show that at least one of the two lattices appears capable of delivering a beam with the desired quality in the longitudinal phase space.

As they are expected to occupy a large portion of the lattice, wiggler insert ions will introduce significant linear and nonlinear perturbations to the single-particle dynamics in the NLC Main Dampig Rings (MDR). The nonlinearities are of particular concernas a sufficiently large Dynamic Aperture (DA) is required for high injection efficiency. The main content of this report is a study of the wigglers impact on the DA of the NLC-MDR latest lattice design. The particle dynamics is modelled by transfer maps calculated by integration through the wiggler fields. For field representation we employed a 3D multipole expansion derived from the field data that were obtained with the aid of a magnet design code. Additional contents of this paper include an investigation of a simplified model of wiggler consisting of a sequence of standard magnet elements (where thin octupoles are used to represent the dominant nonlinearities) and the suggestion of a possible correction scheme to compensate the wiggler nonlinearities.