Electron Cyclotron Resonances in Electron Cloud Dynamics (original) (raw)
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Electron cloud cyclotron resonances in the presence of a short-bunch-length relativistic beam
Physical Review Special Topics - Accelerators and Beams, 2008
Computer simulations using the 2D code "POSINST" were used to study the formation of the electron cloud in the wiggler section of the positron damping ring of the International Linear Collider. In order to simulate an x-y slice of the wiggler (i.e., a slice perpendicular to the beam velocity), each simulation assumed a constant vertical magnetic field. At values of the magnetic field where the cyclotron frequency was an integral multiple of the bunch frequency, and where the field strength was less than approximately 0.6 T, equilibrium average electron densities were up to three times the density found at other neighboring field values. Effects of this resonance between the bunch and cyclotron frequency are expected to be non-negligible when the beam bunch
Investigation into electron cloud effects in the International Linear Collider positron damping ring
Physical Review Special Topics - Accelerators and Beams, 2014
We report modeling results for electron cloud buildup and instability in the International Linear Collider positron damping ring. Updated optics, wiggler magnets, and vacuum chamber designs have recently been developed for the 5 GeV, 3.2-km racetrack layout. An analysis of the synchrotron radiation profile around the ring has been performed, including the effects of diffuse and specular photon scattering on the interior surfaces of the vacuum chamber. The results provide input to the cloud buildup simulations for the various magnetic field regions of the ring. The modeled cloud densities thus obtained are used in the instability threshold calculations. We conclude that the mitigation techniques employed in this model will suffice to allow operation of the damping ring at the design operational specifications.
Electron cloud in the wigglers of the position dampling ring of the international linear collider
The ILC positron damping ring comprises hundreds of meters of wiggler sections, where many more photons than in the arcs are emitted, and with the smallest beam-pipe aperture of the ring. A significant electron-cloud density can therefore be accumulated via photo-emission and via beam-induced multipacting. In field-free regions the electron-cloud build up may be suppressed by adding weak solenoid fields, but the electron cloud remaining in the wigglers as well as in the arc dipole magnets can still drive single-bunch and multi-bunch beam instabilities. This paper studies the electron-cloud formation in an ILC wiggler section for various scenarios, as well as its character, and possible mitigation schemes.
Electron-cloud effects in the TESLA and CLIC positron damping rings
2005
Damping rings reduce the emittances delivered by the particle sources to the small values required for the linear collider. Electron-cloud effects in such a damping ring can cause transverse single bunch instabilities leading finally to an emittance blow up. In this paper, the density of the electron cloud is calculated for the beam and vacuum chamber parameters of the TESLA and CLIC damping rings. The arc and the damping wiggler section are studied separately. For the TESLA dogbone ring also the electron cloud in the long straight sections is investigated. The distribution of photons incident on the vacuum chamber around either ring is simulated for various antechamber parameters, in order to estimate the local production rates of photoelectrons, which is a critical parameter for the electron build up. From the computed final electron densities, an effective transverse single bunch wakefield due to the electron cloud is obtained and a first assessment made of the resulting single-bunch instabilities. Both analytical estimates and numerical simulations suggest that, for the TESLA damping ring, the design bunch intensity is below the threshold of the electron-driven single-bunch instability, if the arcs and the wigglers are equipped with an antechamber intercepting 90% of the photons, if synchrotron-radiation masks or additional bending magnets are added to protect the long straights, and if the maximum secondary emission yield is δ max ≤ 1.6. According to the numerical simulations a special coating of the wiggler vacuum chamber by a material with a low secondary emission yield would be necessary to keep the electron cloud density below 2.0 × 10 12 m −3. In the arcs of the CLIC damping ring about 99% to 99.9% of the photons need to be absorbed by antechambers, which looks possible from photon-flux simulations. For the CLIC wiggler, the antechamber absorption efficiency should be about 95% or higher and the maximum secondary yield δ max ≤ 1.2, in order to avoid single-bunch blow up due to the electron cloud. The results for CLIC are similar to those for the NLC/GLC damping ring [1]. The CLIC requirements may become more relaxed as the design parameters evolve towards lower bunch charges.
Japanese Journal of Applied Physics, 2011
In this paper, the effects of electron cloud are discussed for the ultra low emittance positron beam in Cornell Electron Storage Ring Test Accelerator (Cesr-TA) and the International Linear Collider (ILC) damping ring. We have investigated the electron-cloud instabilities with Cesr-TA which has been operating to experiment for the ILC damping ring with different positron beam energies: 2 and 5 GeV. The electron phase factor, ! e;y z =c, is given differently to each case. The single-bunch instability is investigated with a simulation based on the strong-strong model by using the simplified lattice. The threshold densities obtained by simulations agree with the predicted values within a factor 1.3. We investigate the effects of the bunch-by-bunch feedback of about 50 turns and non-zero dispersion. The simulation results show that the feedback system suppresses the dipole motion and increases the threshold density in 2 GeV case, but is less effective in 5 GeV case. The threshold densities are degraded with non-zero dispersion in both cases, but the rates of degradation appear differently. We discuss an incoherent emittance growth using the realistic lattice model for Cesr-TA. Below the threshold, the incoherent emittance growth may not be serious in Cesr-TA and the ILC damping ring.
2003
In the beam pipe of the Main Damping Ring (MDR) of the Next Linear Collider (NLC), ionization of residual gasses and secondary emission give rise to an electroncloud which stabilizes to equilibrium after few bunch trains. In this paper, we present recent computer simulation results for the main features of the electron cloud at the NLC and preliminary simulation results for the TESLA main damping rings, obtained with the code POSINST that has been developed at LBNL, and lately in collaboration with SLAC, over the past 7 years. Possible remedies to mitigate the effect are also discussed. We have recently included the possibility to simulate different magnetic field configurations in our code including solenoid, quadrupole, sextupole and wiggler. * Work supported by the US DOE under contracts DE-AC03-76SF00515 and DE-AC03-76SF00098.
Mitigation of electron cloud effects in the FCC-ee collider
EPJ Techniques and Instrumentation
Electron clouds forming inside the beam vacuum chamber due to photoemission and secondary emission may limit the accelerator performance. Specifically, the electron clouds can blow up the vertical emittance of a positron beam, through a head-tail-type single-bunch instability, if the central electron density exceeds a certain threshold value, that can be estimated analytically. Using the codes PyECLOUD and VSim, we carried out detailed simulations of the electron-cloud build up for the main arcs and the damping ring of the FCC-ee collider, in order to identify the effective photoemission rate and secondary emission yield required for achieving and maintaining the design emittance. To this end, we present the simulated electron density at the centre of the beam pipe for various bunch spacings, secondary emission yields, and photoemission parameters, in the damping ring and in the arcs of the collider positron ring. To gain further insight into the underlying dynamics, the obtained sp...
Electron Cloud Build Up and Instability in the CLIC Damping Rings
Electron cloud can be formed in the CLIC positron damping ring and cause intolerable tune shift and beam instability. Build up simulations with the Faktor2 code, developed at CERN, have been done to predict the cloud formation in the arcs and wigglers of the damping rings. HEADTAIL simulations have been used to study the effect of this electron cloud on the beam and assess the thresholds above which the electron cloud instability would set in.