Investigation of voltage breakdown caused by microparticles
Degradation of RF accelerating cavities caused by field emission currently limits the design of future linear accelerators. When field emission is the problem, foreign particles often deserve the blame, but they can be "processed" away if the cavity electric field is high enough to initiate voltage breakdown near the particle site, in which case the troublesome particle vaporizes, leaving behind a crater surrounded by a starburst-shaped feature. Severe cratering, however, erodes cavity surfaces to the point of significantly diminished acceleration capability. Breakdown events producing craters and starbursts. similar to those seen in RF cavities can also be incited by a DC electric field. After intentionally contaminating niobium and copper cathodes with different kinds of micron-sized particles, we used scanning electron microscopes with EDX and AES capabilities to obtain "before" and "after" pictures of particles that vaporized under DC electric fields between 30 and 150 MV/m.

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: 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: 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 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: 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: Limit on B(s)0 oscillation using a jet charge method
abstract: A lower limit is set on the B_{s}^{0} meson oscillation parameter \Delta m_{s} using data collected from 1991 to 1994 by the ALEPH detector. Events with a high transverse momentum lepton and a reconstructed secondary vertex are used. The high transverse momentum leptons are produced mainly by b hadron decays, and the sign of the lepton indicates the particle/antiparticle final state in decays of neutral B mesons. The initial state is determined by a jet charge technique using both sides of the event. A maximum likelihood method is used to set a lower limit of \, \Delta m_{s}. The 95\% confidence level lower limit on \Delta m_s ranges between 5.2 and 6.5(\hbar/c^{2})~ps^{-1} when the fraction of b quarks from Z^0 decays that form B_{s}^{0} mesons is varied from 8\% to 16\%. Assuming that the B_{s}^{0} fraction is 12\%, the lower limit would be \Delta m_{s} 6.1(\hbar/c^{2})~ps^{-1} at 95\% confidence level. For x_s = \Delta m_s \, \tau_{B_s}, this limit also gives x_s 8.8 using the B_{s}^{0} lifetime of \tau_{B_s} = 1.55 \pm 0.11~ps and shifting the central value of \tau_{B_s} down by 1\sigma.

title: Search for supersymmetric particles using acoplanar charged-particle pairs from Z0 decays
abstract: We have performed a search for supersymmetric particles using acoplanar pairs of oppositely-charged particles in decays of the Z0. In 0.53 pb−1 of integrated luminosity near the Z0 peak, we observe two events where approximately four are expected from background, allowing limits to be extended on combined photino and slepton masses, and also on combined photino and chargino masses.

title: Search for supersymmetric particles with R-parity violation in Z decays
abstract: Searches for supersymmetric particles produced in e+e− interactions at the Z peak have been performed under the assumptions that R-parity is not conserved, that the dominant R-parity violating coupling involves only leptonic fields, and that the lifetime of the lightest supersymmetric particle can be neglected. In a data sample collected by the ALEPH detector at LEP up to 1993, and corresponding to almost two million hadronic Z decays, no signal was observed. As a result, supersymmetric particle masses and couplings are at least as well constrained as under the usual assumption of R-parity conservation.

title: Measurement of the neutral to charged current cross section ratio in neutrino and antineutrino interactions
abstract: We report on the analysis of inclusive neutral current events produced in neutrino and antineutrino narrow band beams. We find for incident neutrino energies in the range 12–200 GeV and for hadron energies above 12 GeV a neutral to charged current cross-section ratio of R v = 0.293 ± 0.010 for incident neutrinos, and R v = 0.35 ± 0.03 for antineutrinos. These ratios are consistent with the Weinberg-Salam model, with sin 2 θ w = 0.24 ± 0.02.

title: Observation of trimuon events produced in neutrino and antineutrino interactions
abstract: We report two trimuon events producedin v interactions. Of these, one is of the charge type −++, not previously reported. In an antineutrino exposure, one candidate of the charge type +−− has been observed. This type of event has also not been reported previously. The combined π → μ and K → μ background for the three events are calculated to be ∼ 0.7 events. The rate relative to charged current events corresponding to these three events is of the order of 4 × 10 −5 .