L. Van Lancker

Increased photoelectron collection efficiency of a photomultiplier in an aerogel Cherenkov counter

Abstract In a small aerogel Cherenkov counter with diffusing walls, an increase of the photoelectron yield by 40% was measured when the voltage across the cathode to first dynode was increased from 0.6 to 1.7 kV on the 11 cm RCA 8854 photomultiplier tube. A comparison is made with results from other experiments. A general formula for diffusion-type counters is given.

Drift chambers operated in the limited streamer mode

Abstract Successful operation of a drift chamber with 10 cm drift in the limited streamer mode is demonstrated. Good results were obtained with a 50-50 argon-isobutane gas mixture. A preliminary search for alternative gas mixtures avoiding the hydrocarbon quencher component is described.

Test of a CMS MSGC tracker prototype in a high-intensity hadron beam

Abstract A set of CMS MicroStrip Gas Chambers (MSGC) was exposed to a high-intensity 3 GeV /c pion beam at a CERN PS facility for a period of two weeks. The performance of the detectors is reported in terms of stability of efficiency and response to minimum ionising particles as well as to more heavily ionising fragments generated by nuclear interactions.

Operation of micro strip gas counters with Ne-DME gas mixtures

The performance of micro-strip gas counters (MSGCs) has been studied with gas mixtures of neon and dimethylether. The setup consisted of two 10 × 10 cm2 MSGC detectors placed in a cosmic ray hodoscope made of twelve drift chambers. Measurements are presented for the collected charge and the detection efficiency. A Monte Carlo simulation has been used to verify our understanding of the efficiency measurements. The simulation has also allowed to estimate the transverse diffusion coefficient of the electrons in the gas and to predict the spatial resolution of the detectors.

The MICROMEGEM detector

Abstract This article introduces the MICROMEGEM detector, a position-sensitive proportional gas counter produced using advanced Printed Circuit Board (PCB) technology. The detector is equipped with a Gas Electron Multiplier (GEM) foil placed 50 μm above a plane of pick-up strips. The GEM produces a first gas amplification which is extended below the GEM foil by applying a strong electric field between the strips and the lower electrode of the GEM. The array of strips is used for read-out to obtain 1-D positional information. We present results on the gas gain, the energy resolution and the rate capability. The behaviour in an intense beam of 300 MeV /c pions in presence of heavily ionizing particles has also been investigated.

Drift chambers with delay line readout operated in the limited streamer mode

Abstract This report presents the performance of drift chambers operated in the limited streamer mode with 9.4 cm maximum drift distance and position sensing along the 4.35 m long anode wire through delay line timing. Using only three timing channels a position resolution of 1×3 mm 2 is obtained over a detector surface of 19×435 cm 2 . In this contribution, the emphasis is mainly put on the performance of the delay line and on the drift behaviour in streamer mode using safe gas mixtures.

The design of a magnetic shielding for an array of photomultipliers in a strong external field

Abstract A magnetic shielding for the photomultipliers of the Silica Aerogel Detector in the European Hybrid Spectrometer is designed. Emphasis is laid on general principles. The effect of flux enhancement, when a group of individual photomultiplier shieldings is aligned along the direction of the magnetic field, is taken into account. The importance of flux measurements in such a design study is stressed. New formulas for the perpendicular and the axial shielding of a number of coaxial cylinders are presented.

OPERATION OF MICROSTRIP GAS COUNTERS WITH DME-BASED GAS MIXTURES

Abstract This paper reports on the operation of MicroStrip Gas Counters (MSGC) with several dimethylether (DME)-based gas mixtures. We present measurements of signal amplitude, detection efficiency and spatial resolution for minimum ionizing particles. We also show measurements of electron drift velocity and transverse diffusion coefficient in the counting gases considered. These results are discussed regarding the use of MSGC’s for tracking at high-energy physics experiments that have to deal with high particle rates.

The forward muon detector of the DELPHI experiment at LEP

Abstract The layout and construction of the muon drift chambers equipping the end caps of the DELPHI detector are described. The performance of this forward muon detection system, determined from cosmic ray tests and data collected during the first year of LEP operation, is presented.

Performance of the delay lines of the delphi forward muon chambers

Abstract This report presents the performance of 4.35 m long delay lines used for position sensing along the anodes of drift chambers operated in the limited-streamer mode. Using only the time difference between the signals at the two ends of the delay line, a spatial resolution ranging from 1.5 to 2.5 mm is obtained, equivalent to 0.06% of the 4.35 m length of the line. The linearity of the time-to-distance relation is also studied.