Simulation of single bunch instabilities driven by electron cloud in the SPS

Photoemission, or gas ionization, and secondary emission can give rise to a quasi-stationary electron cloud inside the beam pipe through a beam-induced multipacting process. We investigate single bunch instabilities driven by a quasi-stationary electron cloud by means of a computer simulation. The model that we apply makes use of two sets of macroparticles for both the bunch particles and for the electrons, which interact at one or more locations along the beam orbit. Two different schemes have been implemented for the electron cloud field calculation (PIC and soft-Gaussian), and their efficiencies are compared. The code is used to simulate possible instability mechanisms in the SPS. The options of a broad-band wake-field and space charge includuced tune spread have ben also introduced in order to follow the bunch evolution under the combined effect of the elctron-cloud and a broad-band impedance

Two-Stream Problems in Accelerators

Electron beams are perturbed by positively charged ions in a similar way as proton and positron beams may be affected by electrons which are generated via gas ionization, photoemission, or multipacting. In particular, the ions or electrons can induce fast instabilities. These instabilities become more severe in accelerators operating with high current or close bunch spacing. They might even affect less intense muon beams during ionization cooling. Theories, simulations and observations of two-stream instabilities between a charged particle beam and either ions or electrons are reviewed

Interplay of Ionization and Sputtering with the Electron Cloud

The electron cloud enhances the generation and accumulation of ions, which in turn might increase both electron density and electron decay time. We report analytical considerations and simulations of ion motion under the combined influence of beam, electron cloud, and various external magnetic fields. From these, we infer ion survival times, ion impact energies and the equilibrium ion density. All of these are shown to be small. Only in a dipole field whose ion cyclotron frequency is resonant with the bunch spacing (2.62 T for hydrogen ions in the LHC) some ions may acquire kinetic energies of several keV. We argue that additional contributions from ion reflection and sputtering are insignificant

Simulation study on the beneficial effect of linear coupling for the transverse mode-coupling instability in the CERN Super Proton Synchrotron

The intensity threshold of the transverse mode-coupling instability in a flat vertical chamber, as in the CERN Super Proton Synchrotron, is much higher in the horizontal plane than in the vertical one. This asymmetry between the transverse planes led us to the idea that linear coupling from skew quadrupoles could be used to increase the intensity threshold. This technique is already applied, for instance, in the CERN Proton Synchrotron, where a slow head-tail horizontal instability due to the resistive-wall impedance is stabilized by linear coupling only, i.e. with neither octupoles nor feedbacks. This paper presents the results of the study of the effect of linear coupling on the transverse mode-coupling instability, using the HEADTAIL simulation code

Single Bunch Instabilities in FCC-ee

FCC-ee is a high luminosity lepton collider with a centre-of-mass energy from 91 to 365 GeV. Due to the machine parameters and pipe dimensions, collective effects due to electromagnetic fields produced by the interaction of the beam with the vacuum chamber can be one of the main limitations to the machine performance. In this frame, an impedance model is required to analyze these instabilities and to find possible solutions for their mitigation. This paper will present the contributions of specific machine components to the total impedance budget and their effects on the beam stability. Single bunch instability thresholds will be estimated in both transverse and longitudinal planes

Electron cloud simulations: Beam instabilities and wakefields

HEADTAIL is a simulation program developed at CERN which is aimed at studying the single-bunch instability arising from the interaction on successive turns of a single bunch with the cloud generated by the previous bunches. The code includes chromaticity, space charge tune spread, broad-band impedance, and detuning with amplitude for more realistic simulation. Examples of application are shown. Transverse and longitudinal wake functions are also outputs of the HEADTAIL code. (20 refs)

Summary of session 2: high intensity effects

The CARE-HHH-APD workshop LHC-LUMI-05 on Scenarios for the LHC Luminosity Upgrade was held in Arcidosso, Italy, from August 31st to September 3rd, 2005. The workshop was organized in four plenary morning sessions supported by afternoon sessions of two parallel working groups on LHC IR Upgrade and High Energy Injectors. In this report we review the presentations and discussions in Session 2, devoted to High-Intensity Effects, emphasizing the suggestions for future studies and pointing out the open issues

Contributions of the SL-AP Group to the Two-Stream Instabilities Workshop

This paper summarizes the presentations and discussions in the session on theory and simulation at the international workshop on Two-Stream Instabilities, held at KEK, September 11-14, 2001

Collective Effect Studies of a Beta Beam Decay Ring

The Beta Beam, the concept of generating a pure and intense (anti) neutrino beam by letting accelerated radioactive ions beta decay in a storage ring called the Decay Ring (DR), is the basis of one of the proposed next generation neutrino oscillation facilities, necessary for a complete study of the neutrino oscillation parameter space. Sensitivities of the unknown neutrino oscillation parameters depend on the DR's ion intensity and of its duty factor (the filled ratio of the ring). Different methods, including analytical calculations and multiparticle tracking simulations, were used to estimate the DR's potential to contain enough ions in as small a part of the ring as needed for the sensitivities. Studies of transverse blow up of the beams due to resonance wake fields show that a very challenging upper limit of the transverse broadband impedance is required to avoid instabilities and beam loss.Comment: NUFACT2010, 3 pages, 2 figure