Beam-beam simulations for separated beams in the LHC

We present beam-beam simulation results from a strong-strong gaussian code for separated beams for the LHC. We focus on the possible detrimental effects of the beam-beam interaction in cases when the beams are: (1) periodically swept about each other, and (2) brought into collision from separated orbits. For 10{sup 5}-turn runs we do not see significant emittance blowup for nominal bunch intensities, although there is significant blowup at intensities 10 times the nominal value

Beam-beam simulations for separated beams

We present beam-beam simulation results from a strong-strong gaussian code for separated beams for the LHC and RHIC. The frequency spectrum produced by the beam-beam collisions is readily obtained and offers a good opportunity for experimental comparisons. Although our results for the emittance blowup are preliminary, we conclude that, for nominal parameter values, there is no significant difference between separated beams and center-on-center collisions

Progress on electron cloud effects calculations for the FNAL main injector

We have studied the response of the beam to an electron cloud for the Fermilab Main Injector using the Quasistatic Model [1] implemented into the particle-in-cell code Warp [2]. Specifically, we have addressed the effects due to varying the beam intensity, electron cloud density and chromaticity. In addition, we have estimated the contribution to emittance evolution due to beam space-charge effects. We have carried out a comparison between how the beam responds at injection energy and at top energy. We also present some results on the validation of the computational model, and report on progress towards improving the computational model

SIMULATION AND ANALYSIS OF MICROWAVE TRANSMISSION THROUGH ANELECTRON CLOUD, A COMPARISON OF RESULTS

Simulation studies for transmission of microwaves through electron clouds show good agreement with analytic results. The electron cloud produces a shift in phase of the microwave. Experimental observation of this phenomena would lead to a useful diagnostic tool for accessing the local density of electron clouds in an accelerator. These experiments are being carried out at the CERN SPS and the PEP-II LER at SLAC and is proposed to be done at the Fermilab main injector. In this study, a brief analysis of the phase shift is provided and the results are compared with that obtained from simulations

Modeling of E-Cloud Build-Up in Grooved Vacuum Chambers using POSINST

Use of grooved vacuum chambers have been suggested as a way to limit electron cloud accumulation in the ILCDR. We report on simulations carried out using an augmented version of POSINST, accounting for e-cloud dynamics in the presence of grooves, and make contact with previous estimates of an effective secondary electron yield for grooved surfaces

Electron Cyclotron Resonances in Electron Cloud Dynamics

We report a previously unknown resonance for electron cloud dynamics. The 2D simulation code"POSINST" was used to study the electron cloud buildup at different z positions in the International Linear Collider positron damping ring wiggler. An electron equilibrium density enhancement of up to a factor of 3 was found at magnetic field values for which the bunch frequency is an integral multiple of the electron cyclotron frequency. At low magnetic fields the effects of the resonance are prominent, but when B exceeds ~;;(2 pi mec/(elb)), with lb = bunch length, effects of the resonance disappear. Thus short bunches and low B fields are required for observing the effect. The reason for the B field dependence, an explanation of the dynamics, and the results of the 2D simulations and of a single-particle tracking code used to elucidate details of the dynamics are discussed

Electron Cloud induced instabilities in the Fermilab Main Injector(MI) for the High Intensity Neutrino Source (HINS) project

The electrostatic particle-in-cell codeWARP is currently being expanded in order to study electron cloud effects on the dynamics of the beam in storage rings. Results for the Fermilab main injector (MI) show the existence of a threshold in the electron density beyond which there is rapid emittance growth. The Fermilab MI is being considered for an upgrade as part of the high intensity neutrino source (HINS) effort, which will result in a significant increasing of the bunch intensity relative to its present value, placing it in a regime where electron-cloud effects are expected to become important. Various results from the simulations using WARP are discussed here

Self-Consistent 3D Modeling of Electron Cloud Dynamics and Beam Response

We present recent advances in the modeling of beam electron-cloud dynamics, including surface effects such as secondary electron emission, gas desorption, etc, and volumetric effects such as ionization of residual gas and charge-exchange reactions. Simulations for the HCX facility with the code WARP/POSINST will be described and their validity demonstrated by benchmarks against measurements. The code models a wide range of physical processes and uses a number of novel techniques, including a large-timestep electron mover that smoothly interpolates between direct orbit calculation and guiding-center drift equations, and a new computational technique, based on a Lorentz transformation to a moving frame, that allows the cost of a fully 3D simulation to be reduced to that of a quasi-static approximation

Stochastic comparisons of distorted variability measures

In this paper, we consider the dispersive order and the excess wealth order to compare the variability of distorted distributions. We know from Sordo (2009a) that the excess wealth order can be characterized in terms of a class of variability measures associated to the tail conditional distribution which includes, as a particular measure, the tail variance. Given that the tail conditional distribution is a particular distorted distribution, a natural question is whether this result can be extended to include other classes of variability measures associated to general distorted distributions. As we show in this paper, the answer is yes, by focussing on distorted distributions associated to concave distortion functions. For distorted distributions associated to more general distortions, the characterizations are stated in terms of the stronger dispersive order.Ministerio de Ciencia e Innovación (proyecto MTM2009-08326) y Consejería de Eonomía, Innovación y Ciencia (proyecto P09-SEJ-4739