119762147
The nature of field emission from microparticles and the ensuing voltage breakdown
In recent years there has been much progress in furthering our understanding of the sources of field emission as well as in tracing the stages from field emission to voltage breakdown. These advances come from microscopic studies (scanning electron microscopy, energy dispersive x-ray analysis, Auger spectroscopy) of field emitters located by DC high voltage scans as well as from field emitters found in microwave cavities. Craters, residues and starbursts found at breakdown sites reveal much about the physics of voltage breakdown. Both experiments and computer simulations show the important role played by gases generated by field emission induced heating.
55994461
FIRST CHARACTERIZATION OF A FULLY SUPERCONDUCTING RF PHOTOINJECTOR CAVITY
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.
37292985
FABRICATION , TREATMENT AND TESTING OF A 1 . 6 CELL PHOTO- INJECTOR CAVITY FOR HZB
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.
31537972
First Considerations Concerning an Optimized Cavity Design for the Main Linac of BERLinPro
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.
120575134
EUROFEL: Europe Tackles Key Issues of Free Electron Lasers
During the last few years Europe has made enormous progress towards free electron laser (FEL)-based research infrastructures. The FLASH facility [1] at DESY in Hamburg, Germany, has been in user operation since the summer of 2005; FERMI@Elettra [2] in Trieste, Italy, is under construction; the European XFEL [3] 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) [4] and the cryomodule test bench (CMTB) [5] 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) [8] at Daresbury Laboratory, UK. They have been strongly supported by the national stakeholders in order to prepare the design of new FEL sources.
59036810
First Demonstration of Electron Beam Generation and Characterization with an All Superconducting Radio-frequency (SRF) Photoinjector
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.
120456635
Inclusive interactions of high-energy neutrinos and antineutrinos in iron
We present results on charged current inclusive neutrino and antineutrino scattering in the neutrino energy range 30–200 GeV. The results include a) total cross-sections; b)y distributions; c) structure functions; and d) scaling violations observed in the structure functions. The results, as well as their comparison with the results of electron and muon inclusive scattering, are in agreement with the expectations of the quark parton model and QCD.
56333277
Hadron production by virtual photons in the quark fragmentation region
We have measured the inclusive electroproduction of positive and negative hadrons in the quark fragmentation region using the streamer chamber at DESY. Data are presented in terms of the variable zp = p/v in the kinematic region 1.8 < W < 2.8 GeV and 0.3 < Q2 < 1.4 GeV2. The positive hadron distributions contain a strong proton component. After subtraction of the proton component and elastic rho events, the distribution (1/σtot) dσ/dzp for positive and negative hadrons agrees well with the corresponding distribution from e+e− annihilation (DORIS data). This behaviour supports the validity of the quark-parton model at surprisingly low Q2 and W.
119402463
Measurements of mean lifetime and branching fractions of b hadrons decaying to J/PSI
From a data sample of 450 000 hadronic events recorded with the ALEPH detector at LEP, 92±10 events are observed containing a J/ψ meson decaying to μ+μ− or e+e−. From these data the measured inclusive branching fraction for a b flavoured hadron to decay to a J/ψ is BR(b→ J/ψX) = (1.21±0.13 (stat.)±0.08 (syst.))%, and the average b hadron lifetime in the events tagged with a J/ψ is τb = 1.35+0.19−0.17±0.05 ps. Five events are observed consistent with the exclusive decay B± → J/ψK± and from these events the exclusive branching fraction is measured to be BR(B± → J/ψK±) = (0.22±0.10±0.02)%. Upper limits for other exclusive branching ratios are given.
122792144
The response and resolution of an iron-scintillator calorimeter for hadronic and electromagnetic showers between 10 GeV and 140 GeV
Abstract The energy resolution and response of a segmented iron-scintillator total absorption calorimeter has been measured for pion energies from 10 to 140 GeV and for electron energies up to 50 GeV. A procedure has been found to weight individual counter responses for hadron showers which results in improved energy resolution at high energies and a nearly linear dependence of response on hadron energy above 30 GeV. There is evidence in the data that this weighting procedure compensates for fluctuations in energy deposition due to the electromagnetic component of the hadronic shower. For an iron sampling thickness of 2.5 cm the hadron energy resolution follows a 0.58 E law, while the resolution for electromagnetic showers is 0.23 E .
120837276
Is There a High Y Anomaly in anti-neutrino Interactions?
We have analyzed data taken in the CERN narrow-band neutrino and antineutrino beams with regard to the ''high-y anomaly'' observed by previous experiments at Fermilab. At neutrino energies between 30 and 200 GeV, the anti ..nu.. and ..nu.. charged-current cross-section ratios and muon-inelasticity distributions disagree with the earlier results. In particular, there is no evidence for energy-dependent effects in the antineutrino data which constitute an important aspect of the alleged anomaly.