MICROSCOPIC INVESTIGATION OF FIELD EMITTERS LOCATED BY THERMOMETRY IN 1.5 GHz SUPERCONDUCTING NIOBIUM CAVITIES
A new high resolution, high speed thermometry system has been built to permit the study of eld emitters in 1.5 GHz superconducting niobium cavities. Following a cavity test, the cavity is dissected for examination of the emitters in an electron microscope. Presented below is a survey of the topographical characterstics and composition of various defects found so far. A correlation between the current characteristics of emitters and their ability to process away was observed. It has been found that plasma production in the vicinity of an emitter is of importance in determining how much heat an emitter deposits on the rf surface as the electric eld in the cavity is increased. In particular, this plasma plays a pivotal role in the extinction of emitters.

title: FABRICATION , TREATMENT AND TESTING OF A 1 . 6 CELL PHOTO- INJECTOR CAVITY FOR HZB
abstract: As an amendment to a CRADA (Cooperative Research and Development Agreement) between Forschungszentrum Dresden (FZD) and JLab we have fabricated and tested after appropriate surface treatment a 1.6 cell, 1300 MHz RRR niobium photo-injector cavity to be used in a demonstration test at HZB. Following a baseline test at JLab, the cavity received a lead spot coating of ~8 mm diameter deposited with a cathode arc at the Soltan Institute on the endplate made from large grain niobium. It had been demonstrated in earlier tests with a DESY built 1.6 cell cavity – the original design – that a lead spot of this size can be a good electron source, when irradiated with a laser light of 213 nm. In the initial test with the lead spot we could measure a peak surface electric field of ~29 MV/m; after a second surface treatment, carried out to improve the cavity performance, but which was not done with sufficient precaution, the lead spot was destroyed and the cavity had to be coated a second time. This contribution reports about the experiences and results obtained with this cavity.

title: FIRST CHARACTERIZATION OF A FULLY SUPERCONDUCTING RF PHOTOINJECTOR CAVITY
abstract: As a first step towards a high brightness, high average current electron source for the BERLinPro ERL a fully superconducting photo-injector was developed by HZB in collaboration with JLab, DESY and the A. Soltan Institute. This cavity-injector ensemble is made up of a 1.6-cell superconducting cavity with a superconducting lead cathode deposited on the half-cell backwall. A superconducting solenoid is used for emittance compensation. This system, including a diagnostics beamline, has been installed in the HoBiCaT facility to serve as a testbed for beam dynamics studies and to test the combination SRF cavity and superconducting solenoid. This paper summarizes the characterization of the cavity in this configuration including Q measurements, dark current tests and field-stability analyses.

title: EUROFEL: Europe Tackles Key Issues of Free Electron Lasers
abstract: During the last few years Europe has made enormous progress towards free electron laser (FEL)-based research infrastructures. The FLASH facility  at DESY in Hamburg, Germany, has been in user operation since the summer of 2005; FERMI@Elettra  in Trieste, Italy, is under construction; the European XFEL  in Hamburg will start construction in summer 2008; and several other FEL projects are being prepared in France, Germany, Italy, Poland, Sweden, Switzerland and the UK. In addition, a number of dedicated test facilities have become available, including the photo-injector test facility (PITZ)  and the cryomodule test bench (CMTB)  at DESY, the HoBiCaT facility for testing superconducting cavities [6] at BESSY, Berlin, Germany, the SPARC facility [7] at INFN-LNF in Frascati, Italy, and the ERL Prototype (ERLP)  at Daresbury Laboratory, UK. They have been strongly supported by the national stakeholders in order to prepare the design of new FEL sources.

title: First Considerations Concerning an Optimized Cavity Design for the Main Linac of BERLinPro
abstract: The Berlin Energy Recovery Linac Project (BERLinPro) is designed to develop and demonstrate CW linac technology and expertise required to drive next-generation Energy Recovery Linacs. Strongly HOM-damped multicell 1.3 GHz cavities are required for the main linac. The optimization of the cavities presented here is primarily based on the CEBAF 1.5 GHz 5-cell high-current cavity design, including HOM waveguide couplers. The cavity was scaled to 1.3 GHz and extended to 7 cells. Modifications to the end group design have also been studied. An effort was also made to reduce the ratio Epk/Eacc while still permitting HOMs to propagate.

title: First Demonstration of Electron Beam Generation and Characterization with an All Superconducting Radio-frequency (SRF) Photoinjector
abstract: In preparation for a high brightness, high average current electron source for the energy recovery linac BERLinPro an all superconducting radio-frequency (SRF) photoinjector is now in operation at Helmholtz-Zentrum Berlin. The aim of this experiment is beam demonstration with a high brightness electron source able to generate short, few ps long pulse length electron bunches from a superconducting (SC) cathode film made of Pb coated on the backplane of a Nb SRF cavity. This paper describes the setup of the experiment, first results from beam measurements and capabilities of the source derived from beam dynamics considerations. In April 2011 the photoinjector generated and accelerated for the first time electron beam. This result marks the highlight of the project running for two years starting with project approval in May 2009.

title: Characteristics of trimuon events observed in high-energy neutrino interactions
abstract: The properties of 76 neutrino-initiated μ − μ − μ + events observed in the CDHS detector in the 350 GeV and 400 GeV wide-band beams at CERN are discussed. For neutrino energies 30 GeV and muon momenta ≳4.5 GeV, the average trimuon rate is (3.0 ± 0.4) × 10 −5 of the single-muon event rate. The experimental distributions are compared with predictions from various models. The data cannot be understood in terms of either heavy-lepton or heavy-quark cascades; no evidence is found for such processes and upper limits for the two possibilities are established. The data can be understood in terms of the normal charged-current process with the additional production of a muon pair by both hadronic and electromagnetic processes.

title: Search for anomalous production of prompt like-sign muon pairs and constraints on physics beyond the standard model with the ATLAS detector
abstract: An inclusive search for anomalous production of two prompt, isolated muons with the same electric charge is presented. The search is performed in a data sample corresponding to 1.6 fb(-1) of integr ...

title: Results of a beam dump experiment at the CERN SPS neutrino facility
abstract: We report results from a beam dump experiment that has been performed at the CERN SPS neutrino facility using the CDHS neutrino counter detector. Limits on dimuon and trimuon production by new penetrating neutral particles are given. A new source of prompt electron and muon neutrinos has been observed giving (1.2±0.4)× 10−7 νe or νμ per incident proton with neutrino angle smaller than 1.85 mrad and Eν > 20 GeV. If these prompt neutrinos are attributed to charmed meson pair production, the inclusive DD production cross section could be of the order of 30 ωb. If axions are existing their production rate relative to π0 mesons is found to be less than 0.5 × 10−8.

title: Measurement of the charged particle multiplicity distribution in hadronic Z decays
abstract: The charged particle multiplicity distribution of hadronic Z decays was measured on the peak of the Z resonance using the ALEPH detector at LEP. Using a model independent unfolding procedure the distribution was found to have a mean 〈n〉=20.85±0.24 and a dispersion D=6.34±0.12. Comparison with lower energy data supports the KNO scaling hypothesis in the energy range GeV. At GeV the shape of the multiplicity distribution is well described by a log-normal distribution, as predicted from a cascading model for multi-particle production. The same model also successfully describes the energy dependence of the mean and width of the multiplicity distribution. A next-to-leading order QCD prediction in the framework of the modified leading-log approximation and local parton-hadron duality is found to fit the energy dependence of the mean but not the width of the charged multiplicity distribution, indicating that the width of the multiplicity distribution is a sensitive probe for higher order QCD or non-perturbative effects.

title: Observation of a neutrino event with four energetic muons