T. Auger

The bremsstrahlung tagged photon beam in Hall B at JLab

We describe the design and commissioning of the photon tagging beamline installed in experimental Hall B at the Thomas Jefferson National Accelerator Facility (JLab). This system can tag photon energies over a range from 20% to 95% of the incident electron energy, and is capable of operation with beam energies up to 6.1 GeV. A single dipole magnet is combined with a hodoscope containing two planar arrays of plastic scintillators to detect energy-degraded electrons from a thin bremsstrahlung radiator. The first layer of 384 partially overlapping small scintillators provides photon energy resolution, while the second layer of 61 larger scintillators provides the timing resolution necessary to form a coincidence with the corresponding nuclear interaction triggered by the tagged photon. The definitions of overlap channels in the first counter plane and of geometric correlation between the two planes are determined using digitized time information from the individual counters. Auxiliary beamline devices are briefly described, and performance results to date under real operating conditions are presented. The entire photon-tagging system has met or exceeded its design goals.

LiSoR, a liquid metal loop for material investigation under irradiation

Abstract LiSoR is a liquid metal loop that will use PSI’s 72 MeV Philips cyclotron to irradiate stressed steel specimens in contact with flowing lead–bismuth with 50 μA proton beam. Liquid metal–solid metal reactions is a joint effort of PSI and SUBATECH with the support from CNRS and the Institute of Physics from Riga. It has been initiated to explore whether or not liquid metal corrosion and liquid metal embrittlement are enhanced under irradiation in the presence of stress. Numerical simulations showed that the damage levels and gas production in thin specimens induced by 72 MeV protons are, within reasonable limits, comparable to those on the inside of the beam window of a spallation target at 600 MeV, while much less radioactivity is produced. The paper describes the basic features of the experiment, the technical concept of the liquid metal loop with a special emphasis on the test section exposed to the proton beam and some of the relevant safety aspects.

A photon calorimeter using lead tungstate crystals for the CEBAF Hall A Compton polarimeter

Abstract A new Compton polarimeter is built on the CEBAF Hall A electron beam line. Performances of 10% resolution and 1% calibration are required for the photon calorimeter of this polarimeter. This calorimeter is built with lead tungstate scintillators coming from the CMS electromagnetic calorimeter R&D. Beam tests of this detector have been made using the tagged photon beam line at MAMI, Mainz, and a resolution of 1.76%⊕2.75%/ E ⊕0.41%/E has been measured.

Crack path in liquid metal embrittlement: experiments with steels and modeling

We review the recent experimental clarification of the fracture path in Liquid Metal Embrittlement with austenitic and martensitic steels. Using state of the art characterization tools (Focused Ion Beam and Transmission Electron Microscopy) a clear understanding of crack path is emerging for these systems where a classical fractographic analysis fails to provide useful information. The main finding is that most of the cracking process takes place at grain boundaries, lath or mechanical twin boundaries while cleavage or plastic flow localization is rarely the observed fracture mode. Based on these experimental insights, we sketch an on-going modeling strategy for LME crack initiation and propagation at mesoscopic scale.

MEMUS – A large solid angle detector for ELFE

Abstract Multiparticle Electroproduction Modular Upgradable Spectrometer (MEMUS) is a large acceptance detector intended to run on the ELFE machine at a luminosity of 10 36 cm −2 s −1 per nucleon with a hydrogen target. The detector is designed to study reactions with multiparticle final states. We present a brief description of the overall detector design and of the ongoing research program on the determination of the adequate characteristics of the different detector components.

Requirements for a large solid angle detector for ELFE

Abstract We present detailed simulations of the MEMUS detector [1] response to both electromagnetic and hadronic background, as well as to a representative set of proposed experiments at ELFE. The aim of this study is to check the adequation of the detector to the requirements of the experiments involving exclusive channels. This study is far from complete, but preliminary design refinements can be inferred. The technical details for the detector components can be found in the write-up of the detector session[2].