European Spallation Source Lattice Design Status

The accelerator of the European Spallation Source (ESS) will deliver 62.5 mA proton beam of 2.0 GeV onto the target, offering an unprecedented beam power of 5 MW. Since the technical design report (TDR) was published in 2013, work has continued to further optimise the accelerator design. We report on the advancements in lattice design optimisations after the TDR to improve performance and flexibility, and reduce cost of the ESS accelerato

Operation and performance of the ATLAS Tile Calorimeter in Run 1

The Tile Calorimeter is the hadron calorimeter covering the central region of the ATLAS experiment at the Large Hadron Collider. Approximately 10,000 photomultipliers collect light from scintillating tiles acting as the active material sandwiched between slabs of steel absorber. This paper gives an overview of the calorimeter’s performance during the years 2008–2012 using cosmic-ray muon events and proton–proton collision data at centre-of-mass energies of 7 and 8TeV with a total integrated luminosity of nearly 30 fb−1. The signal reconstruction methods, calibration systems as well as the detector operation status are presented. The energy and time calibration methods performed excellently, resulting in good stability of the calorimeter response under varying conditions during the LHC Run 1. Finally, the Tile Calorimeter response to isolated muons and hadrons as well as to jets from proton–proton collisions is presented. The results demonstrate excellent performance in accord with specifications mentioned in the Technical Design Report

EFFECT OF THE FIELD MAPS ON THE BEAM DYNAMICS OF THE ESS DRIFT TUBE LINAC

In the beam dynamics design and modelling of the Eu- ropean Spallation Source (ESS) Drift Tube Linac (DTL) simplified models have been used for the focusing and ac- celerating elements. Since the high current requires precise control of the beam to analyze the losses it is useful to per- form the beam dynamics simulations by using accurate field maps of the focusing and accelerating elements. In this pa- per the effects of the 3D-field maps on the beam dynamics of the ESS DTL are presented

Pulsed DC High Field Measurements of Irradiated and Non-Irradiated Electrodes of Different Materials

Beam loss occurs in Radio Frequency Quadrupoles (RFQ), and has been observed in the H⁻ linear accelerator Linac4 (L4) at CERN. To determine if beam loss can induce breakdowns, and to compare the robustness of different materials, tests have been done using pulsed high-voltage DC systems. Electrical breakdown phenomena and conditioning processes have been studied using these systems. Cathodes of different materials were irradiated with 1.2x10¹⁹ H⁻ p/cm², the estimated beam loss of the L4 RFQ over 10 days. The irradiated electrodes were installed in a system to observe if the irradiated area coincided with the breakdown locations, with pulsing parameters similar to the RFQ. Tests of irradiated and non-irradiated electrodes of the same material were done for comparison. The main difference observed was an increase in the number of breakdowns during the initial conditioning that returned to non-irradiated sample values with further running. Visual observations after irradiation show the beam centre and a halo the same diameter of the beam pipe. Breakdown clusters occur in the centre and halo regions, suggesting irradiation is not the only factor determining the breakdown probability

Microscopy Investigation on Different Materials After Pulsed High Field Conditioning and Low Energy H−^{-} Irradiation

During operation the RFQ (Radio-Frequency-Quadrupole) of the LINAC4 at CERN is exposed to high electric fields which can lead to vacuum breakdown. It is also subject to beam loss that can cause surface modification, including blistering, which can result in reduced electric field handling and an increased breakdown rate. An experimental study has been made to identify materials with high electric field capability and robustness to low-energy irradiation. In this paper we briefly discuss the selection criteria, and we analyse these materials investigating their metallurgical properties using advanced microscopic techniques such as Scanning Electron Microscope, Electron Back Scattered Diffraction, Energy-dispersive X-ray Spectroscopy and conventional optical microscopy. These allow to observe and characterize the different materials on a micro and a nanoscale and to compare results before and after irradiation and breakdown testing