Measurement of Electron Clouds in Large Accelerators by Microwave Dispersion

Clouds of low energy electrons in the vacuum beam pipes of accelerators of positively charged particle beams present a serious limitation for operation at high currents. Furthermore, it is difficult to probe their density over substantial lengths of the beam pipe. We have developed a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave transmitted over a section of the accelerator and used it to measure the average electron cloud density over a 50 m section in the positron ring of the PEP-II collider at the Stanford Linear Accelerator Center

CERN SPS Impedance in 2007

Each year several measurements of the beam coupling impedance are performed in both longitudinal and transverse planes of the CERN Super Proton Synchrotron to keep track of its evolution. In parallel, after the extensive and successful campaign of identification, classification and cure of the possible sources of (mainly longitudinal) impedance between 1998 and 2001, a new campaign (essentially for the transverse impedance this time) has started few years ago, in view of the operation of the SPS with higher intensity for the LHC luminosity upgrade. The present paper summarizes the results obtained from the measurements performed over the last few years and compares them to our predictions. In particular, it reveals that the longitudinal impedance is reasonably well understood and the main contributors have already been identified. However, the situation is quite different in the transverse plane: albeit the relative evolution of the transverse impedance over the last few years can be well explained by the introduction of the nine MKE kickers necessary for beam extraction towards the LHC, significant contributors to the SPS transverse impedance have not been identified yet

Tune shift induced by nonlinear resistive wall wake field of flat collimator

We present formulae for the coherent and incoherent tune shifts due to the nonlinear resistive wall wake field for a single beam traveling between two parallel plates. In particular, we demonstrate that the nonlinear terms of the resistive-wall wake field become important if the gap between the plates is comparable to the transverse rms beam size. We also compare the theoretically predicted tune shift as a function of gap size with measurements for an LHC prototype graphite collimator in the CERN SPS and with simulations

SPS Impedance

For many years several measurements of the beam coupling impedance have been performed each year in both longitudinal and transverse planes of the CERN Super Proton Synchrotron to keep track of the evolution of its hardware. Copious types of equipments had to be modified or added in the past to allow the SPS to produce the nominal LHC beam. The next challenge would be the operation of the SPS with higher intensity for the LHC luminosity upgrade, which requires a good knowledge of the machine impedance and in particular of its major contributors. The current understanding of the measurements performed over the last few years is presented in this paper. In particular, this analysis reveals that the longitudinal impedance is reasonably well understood, while the situation is less satisfactory in the transverse planes, where about half of the measured impedance still needs to be identified

Microwave Transmission Measurements of the Electron Cloud Density In The Positron Ring of PEP-II

Clouds of electrons in the vacuum chambers of accelerators of positively charged particle beams present a serious limitation for operation of these machines at high currents. Because of the size of these accelerators, it is difficult to probe the low energy electron clouds over substantial lengths of the beam pipe. We applied a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave which is independently excited and transmitted over a straight section of the accelerator. The modulation in the wave transmission which appear to increase in depth when the clearing solenoids are switched off, seem to be directly correlated to the electron cloud density in the section. Furthermore, we expect a larger phase shift of a wave transmitted through magnetic dipole field regions if the transmitted wave couples with the gyration motion of the electrons. We have used this technique to measure the average electron cloud density (ECD) specifically for the first time in magnetic field regions of a new 4-dipole chicane in the positron ring of the PEP-II collider at SLAC. In this paper we present and discuss the measurements taken in the Low Energy Ring (LER) between 2006 and 2008

Transverse Impedance of LHC Collimators

The transverse impedance in the LHC is expected to be dominated by the numerous collimators, most of which are made of Fibre-Reinforced-Carbon to withstand the impacts of high intensity proton beams in case of failures, and which will be moved very close to the beam, with full gaps of few millimetres, in order to protect surrounding super-conducting equipments. We present an estimate of the transverse resistive-wall impedance of the LHC collimators, the total impedance in the LHC at injection and top energy, the induced coupled-bunch growth rates and tune shifts, and finally the result of the comparison of the theoretical predictions with measurements performed in 2004 and 2006 on a prototype collimator installed in the SPS

New Insight Into Avian Papillomavirus Ecology and Evolution From Characterization of Novel Wild Bird Papillomaviruses

Viruses in the family Papillomaviridae have circular dsDNA genomes of approximately 5.7–8.6 kb that are packaged within non-enveloped, icosahedral capsids. The known papillomavirus (PV) representatives infect vertebrates, and there are currently more than 130 recognized PV species in more than 50 genera. We identified 12 novel avian papillomavirus (APV) types in wild birds that could represent five distinct species and two genera. Viruses were detected in paired oropharyngeal/cloacal swabs collected from six bird species, increasing the number of avian species known to harbor PVs by 40%. A new duck PV (DuPV-3) was found in mallard and American black duck (27.6% estimated prevalence) that was monophyletic with other known DuPVs. A single viral type was identified in Atlantic puffin (PuPV-1, 9.8% estimated prevalence), while a higher genetic diversity was found in other Charadriiformes. Specifically, three types [gull PV-1 (GuPV-1), -2, and -3] were identified in two gull species (estimated prevalence of 17% and 2.6% in American herring and great black-backed gull, respectively), and seven types [kittiwake PV-1 (KiPV-1) through -7] were found in black-legged kittiwake (81.3% estimated prevalence). Significantly higher DuPV-3 circulation was observed in spring compared to fall and in adults compared to juveniles. The studied host species’ tendencies to be in crowded environments likely affect infection rates and their migratory behaviors could explain the high viral diversity, illustrating how host behavior can influence viral ecology and distribution. For DuPV-3, GuPV-1, PuPV-1, and KiPV-2, we obtained the complete genomic sequences, which showed the same organization as other known APVs. Phylogenetic analyses showed evidence for virus–host co-divergence at the host taxonomic levels of family, order, and inter-order, but we also observed that host-specificity constraints are relaxed among highly related hosts as we found cross-species transmission within ducks and within gulls. Furthermore, the phylogeny of viruses infecting the Charadriiformes did not match the host phylogeny and gull viruses formed distinct monophyletic clades with kittiwake viruses, possibly reflecting past host-switching events. Considering the vast PV genotype diversity in other hosts and the large number of bird species, many more APVs likely remain to be discovered

The CERN PS multi-turn extraction based on beam splittting in stable islands of transverse phase space: Design Report

Since 2001 considerable effort has been devoted to the study of a possible replacement of the continuous-transfer extraction mode from the PS to the SPS. Such an approach, called Multi-Turn Extraction (MTE), is based on capture of the beam inside stable islands of transverse phase space, generated by sextupoles and octupoles, thanks to a properly chosen tune variation. Both numerical simulations and measurements with beam were performed to understand the properties of this new extraction mode. The experimental study was completed at the end of 2004 and by the end of 2005 a scheme to implement this novel approach in the PS machine was defined and its performance assessed. This design report presents the outcome of the studies undertaken both in terms of technical issues as well as of resources necessary to implement the proposed scheme

The SPL (II) at CERN, a Superconducting 3.5 GeV H- Linac

A revision of the physics needs and recent progress in the technology of superconducting (SC) RF cavities have triggered major changes in the design of a SC H-linac at CERN. With up to 5MW beam power, the SPL can be the proton driver for a next generation ISOL-type radioactive beam facility (âEURISOLâ) and/or supply protons to a neutrino () facility (conventional superbeam + beta-beam or -factory). Furthermore the SPL can replace Linac2 and the PS booster (PSB), improving significantly the beam performance in terms of brightness, intensity, and reliability for the benefit of all proton users at CERN, including LHC and its luminosity upgrade. Compared with the first conceptual design, the beam energy is almost doubled (3.5GeV instead of 2.2 GeV) while the length is reduced by 40%. At a repetition rate of 50 Hz, the linac reuses decommissioned 352.2MHz RF equipment from LEP in the low-energy part. Beyond 90MeV the RF frequency is doubled, and from 180MeV onwards high-gradient SC bulkniobium cavities accelerate the beam to its final energy of 3.5GeV. This paper presents the overall design approach, together with the technical progress since the first conceptual design in 2000

Linac4 Technical Design Report

Linac4 is an H- linear accelerator, intended to replace Linac2 as injector to the PS Booster (PSB). By delivering to the PSB a beam at 160 MeV energy, Linac4 will provide the conditions to double the brightness and intensity of the beam from the PSB, thus removing the first bottleneck towards higher brightness for the LHC and simplifying operation. Moreover, this new linac constitutes an essential component of any of the envisaged LHC upgrade scenarios and could open the way to future extensions of the CERN accelerator complex towards higher performance. This Technical Design Report presents a detailed technical overview of the Linac4 design as it stands at end 2006