A Laser Based Instrument for MWPC Wire Tension Measurement

A fast and simple method for the measurement of the mechanical tension of wires of Multi Wires Proportional Chambers (MWPCs) is described. The system is based on commercial components and does not require any electrical connection to the wires or electric or magnetic field. It has been developed for the quality control of MWPCs of the Muon Detector of the LHCb experiment in construction at CERN. The system allows a measurement of the wire tension with a precision better than 0.5% within 3-4 seconds per wir

Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET

The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR

Relationship of edge localized mode burst times with divertor flux loop signal phase in JET

A phase relationship is identified between sequential edge localized modes (ELMs) occurrence times in a set of H-mode tokamak plasmas to the voltage measured in full flux azimuthal loops in the divertor region. We focus on plasmas in the Joint European Torus where a steady H-mode is sustained over several seconds, during which ELMs are observed in the Be II emission at the divertor. The ELMs analysed arise from intrinsic ELMing, in that there is no deliberate intent to control the ELMing process by external means. We use ELM timings derived from the Be II signal to perform direct time domain analysis of the full flux loop VLD2 and VLD3 signals, which provide a high cadence global measurement proportional to the voltage induced by changes in poloidal magnetic flux. Specifically, we examine how the time interval between pairs of successive ELMs is linked to the time-evolving phase of the full flux loop signals. Each ELM produces a clear early pulse in the full flux loop signals, whose peak time is used to condition our analysis. The arrival time of the following ELM, relative to this pulse, is found to fall into one of two categories: (i) prompt ELMs, which are directly paced by the initial response seen in the flux loop signals; and (ii) all other ELMs, which occur after the initial response of the full flux loop signals has decayed in amplitude. The times at which ELMs in category (ii) occur, relative to the first ELM of the pair, are clustered at times when the instantaneous phase of the full flux loop signal is close to its value at the time of the first ELM

Asymmetric and double-cathode-pad wire chambers for the LHCb muon system

We present results from two types of Multi-Wire Proportional Chambers (MWPCs) with wire pitch of 1.5 mm and cathode–cathode distance of 5 mm intended for triggering purposes in the LHCb experiment. Both prototypes use cathode readout because this allows arbitrary segmentation in order to achieve the required granularity. One MWPC prototype uses a symmetric wire–cathode distance (2.5/2.5 mm) with double cathode readout, which doubles the signal compared to reading only one cathode. The second prototype uses an asymmetric wire–cathode distance (1.25/3.75 mm) with single cathode readout which also doubles the signal and in addition reduces the width of the induced charge distribution and therefore reduces the crosstalk for small cathode pads. We also performed a dedicated optimization of readout traces and guard traces in order to reduce the pad–pad crosstalk. Both prototypes show a few hundred volts of operating plateau defined as the region with 99% efficiency in a 20 ns time window. Close to the plateau end, a time resolution of better than 3 ns was achieved

Results obtained with the first four gap MWPC prototype chamber

Results of measurements made with a full size four gap multi-wire proportional chamber prototype for the inner part of the LHCb muon system are presented. Special emphasis has been placed on the comparisons between the calculated and measured detector capacitances of the wire and cathode pads. The efficiency and cross talk in the case of a combined anode-cathode readout of the prototype were measured in a test beam. In general the properties of the chamber are well understood, although the cause of instability in the front end electronics needs to be resolved. With the possible exception of cross talk between anode wire pads the prototype fulfils the requirements for the LHCb muon system. Further studies with this prototype are planned and will update these results

Wire pad chambers and cathode pad chambers for the LHCb muon system

A proposal for Wire-Pad-Chambers and Cathode-Pad-Chambers for the LHCb Muon system is presented. It is shown that a single technology satisfies the requirements of almost the entire detector, garanteeing maximum uniformity. The muon system layout based on this technology is shown, and the chamber geometry specifications together with electronics considerations are discussed. An overview of prototype results are presented, followed by considerations on ageing. Finally construction and cost issues are outlined

A wire tension meter for the LHCb muon chambers

A wire tension meter has been developed for the multiwire chambers of the LHCb muon detector. The wire tension is deduced from its mechanical resonance frequency. In the LHCb muon chambers, the wires are electrically connected in group of 14, so that the wire excitation method based on the interaction between a current sent into a wire and an external magnetic field is difficult to be used. In our system the wire under test is forced to oscillate by a periodic potential difference applied between that wire and a non-oscillating sense wire placed parallel and close to it. This oscillation produces a variation of the capacitance between these two wires which is measured by a high precision digital electronic circuit. At the resonance frequency this capacitance variation is maximum. The system has been systematically investigated and its parameters optimized. In the range 0.4 - 1 N a very good agreement was found between the mechanical tension measured by this system and by a dynamometer

Automated wire tension measurement system for LHCb muon chambers RID B-4806-2009

A wire tension meter has been developed for the multi-wire proportional chambers of the LHCb muon detector. The wire tension is deduced from its mechanical resonance frequency. In the LHCb muon chambers. the wires are 2 mm apart and electrically connected in groups of 3-32, so that the wire excitation system must he precisely positioned with respect to the wire to be tested. This wire is forced to oscillate by it periodic high voltage applied between that wire and it non-oscillating "sense wire" placed parallel and close to it. This oscillation produces it variation of the capacitance between these two wires which is measured by a high precision digital electronic circuit. At the resonance frequency this capacitance variation is maximum. The system has been systematically investigated and its parameters were optimized. In the range 0.4-1 N a good agreement is found between the mechanical tension measured by this system and by a dynamometer. (c) 2005 Elsevier B.V. All rights reserved