56307984
FIRST RF TESTS IN THE HOBICAT SUPERCONDUCTING TEST FACILITY AT BESSY
In preparation for the construction of the BESSY-FEL User Facility, BESSY recently completed the installation of the HoBiCaT cryogenic test facility for superconducting RF (SRF) TESLA cavity units [1], including all ancillary devices (helium tank, input coupler, tuner, magnetic shielding). It is designed to house two such units in a configuration similar to that envisaged for the superconducting CW linac of the BESSY FEL. Commissioning of the facility is now complete and the first TTF-III RF coupler and cavity unit has been tested. In particular, the complete production, cleaning and assembly of the cavity unit was carried out by industry. These tests thus serve as a first step at qualifying industrial partners for series production of such systems, which will be essential for the future construction of SRF based light sources.
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.
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.
198946223
CHARACTERISATION OF MICROPHONICS IN HOBICAT
The HoBiCaT test-facility at BESSY, which is designed for cryogenic testing of superconducting TESLA units has been equipped with a 9-cell TESLA-type cavity. Mechanical vibrations in the cryostat result in microphonic detuning of the cavity resonance. These microphonics have been characterized, and their sources analyzed, including the impact of operating conditions such as LHe pressure, cavity field and heater power. Furthermore, the mechanical transfer functions needed for the eventual compensation of the microphonics have been recorded. INTRODUCTION For CW operation of a superconducting, TESLA-type cavity microphonics represent the largest disturbance of the resonant frequency. In particular at a small bandwidth Δf = ω/QL, according to the equation P ∝ 1 + (δf) 2 (Δf)2 (1) the microphonics δf lead to a significant increase of the generator power P, which is required to maintain a constant cavity field. Therefore it is highly desirable to minimize the microphonics. Measurements characterizing the microphonics and their impact on the cavity operation are presented below. The perspectives on possible countermeasures are described elsewhere [1]. MICROPHONICS MEASUREMENTS Microphonics have been recorded in two different ways. In a first method, the RF-feedback signal, see Figure 1, is recorded over time. This is preferably done in open loop configuration, because obtaining a calibration factor is more straightforward here, than in closed loop configuration. A second method utilizes the sensor-actuator design of the piezo tuner to record the induced piezoelectric voltage over time. In this design, two high-voltage piezos are attached to the tuner, thus piezoelectric forces can be exercised on the cavity and measured simultaneously. The latter is only an indirect method, as the mechanical influence from cavity and tank on the frequency response does not necessarily lead to a linear relationship between cavityand piezo position. The results presented here were solely obtained from the RF-feedback signal. ∗Work funded by the European Commission in the Sixth Framework Program, contract No. 011935 EUROFEL. Input coupler piezo
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.
53355048
Multipacting in 1 . 5-GHz superconducting niobium cavities of the CEBAF shape ∗
We present definitive thermometric evidence of two-point multipacting in the CEBAF cavity shape, starting at Epk = 30 MV/m (at 1.5 GHz). With the aid of high speed thermometry, we were able to record fleeting multipacting events near the cavity equator. Short term electron bombardment eliminates the multipacting barrier. Numerical trajectory simulations presented here also confirm the experimental data. Although multipacting itself could be processed away and did not limit the cavity performance, it is shown that the quenches due to the electron bombardment increase the cavity’s residual resistance by creating and trapping magnetic flux.
120805024
Search for First Generation Scalar Leptoquarks in pp Collisions at $\sqrt{s}=7$ TeV with the ATLAS Detector
We report a search for first generation scalar leptoquarks using 1.03 fb−1 of proton–proton collisions data produced by the Large Hadron Collider at and recorded by the ATLAS experiment. Leptoquarks are sought via their decay into an electron or neutrino and a quark, producing events with two oppositely charged electrons and at least two jets, or events with an electron, missing transverse momentum and at least two jets. Control data samples are used to validate background predictions from Monte Carlo simulation. In the signal region, the observed event yields are consistent with the background expectations. We exclude at 95% confidence level the production of first generation scalar leptoquark with masses when assuming the branching fraction of a leptoquark to a charged lepton is equal to 1.0 (0.5).
118364778
Measurement of charge asymmetry in hadronic Z decays
A significant charge asymmetry is observed in the hadronic Z decays with the ALEPH detector at LEP. The asymmetry expressed in terms of the difference in momentum weighted charges in the two event hemispheres is measured to be − = −0.0084±0.0015 (stat.) ±0.0004 (exp. sys.). In the framework of the standard model this can be interpreted as a measurement of the effective electroweak mixing angle, sin2Ow (Mz2=0.2300±0.0034 (stat.) ±0.0010 (exp. sys.) ±0.0038 (theor. sys.) or of the ratio of the vector to axual- vector coupling costants of the electron, gvegAe=+0.073±0.024.
116813021
Results of a beam dump experiment at the CERN SPS neutrino facility
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.
59856495
LHC computing grid : Technical design report
23468075
Status Report of the DPHEP Study Group: Towards a Global Effort for Sustainable Data Preservation in High Energy Physics
Data from high-energy physics (HEP) experiments are collected with significant financial and human effort and are mostly unique. An inter-experimental study group on HEP data preservation and long-term analysis was convened as a panel of the International Committee for Future Accelerators (ICFA). The group was formed by large collider-based experiments and investigated the technical and organisational aspects of HEP data preservation. An intermediate report was released in November 2009 addressing the general issues of data preservation in HEP. This paper includes and extends the intermediate report. It provides an analysis of the research case for data preservation and a detailed description of the various projects at experiment, laboratory and international levels. In addition, the paper provides a concrete proposal for an international organisation in charge of the data management and policies in high-energy physics.