T. J. Jones

The evaporative cooling system for the ATLAS inner detector

This paper describes the evaporative system used to cool the silicon detector structures of the inner detector sub-detectors of the ATLAS experiment at the CERN Large Hadron Collider. The motivation for an evaporative system, its design and construction are discussed. In detail the particular requirements of the ATLAS inner detector, technical choices and the qualification and manufacture of final components are addressed. Finally results of initial operational tests are reported. Although the entire system described, the paper focuses on the on-detector aspects. Details of the evaporative cooling plant will be discussed elsewhere.

The microdot gas avalanche chamber: an investigation of new geometries

Abstract The gains of the microstrip and microgap gas avalanche chambers are limited to below gains of 5 × 10 3 by geometrical and gas properties. In order to increase the maximum gain to greater than 2 × 10 4 a new detector geometry, the microdot, is proposed that can be produced at a standard silicon MOS microfabrication facility at similar cost to present microstrip gas detectors. In addition to charged particle tracking, the new geometry is also well suited to imaging applications. The operating characteristics of the new device have been investigated using a numerical simulation and a comparison with conventional strip geometries is presented. These results show that the microdot geometry reaches higher gas gains than the strip-like geometries, for the same set of electrode potentials, with a reduced cathode electric field enhancing operational stability.

First experimental results from a microdot gas avalanche detector integrated onto a silicon wafer

First results on the voltage dependence of the gas gain of a microdot detector are presented. No variation of the gas gain with rate is observed up to a measured maximum rate of 4 x lo3 X-rays/mm*/s. Some possible applications of this detector are discussed.

Initial investigations of the performance of a microstrip gas-avalanche chamber fabricated on a thin silicon-dioxide substrate

Abstract We report on the construction of a mu-strip gas-avalanche chamber, designed such that the effective thickness of the insulating dielectric is ∼ 3 μm. Experimental results are presented on the initial observation of pulses from the chamber originating from the energy depositions of X-rays from an Fe 55 source.

Annealing effects on irradiated n+n silicon detectors

The performance of ATLAS forward region full-sized n+n prototype silicon micro-strip detectors has been studied after irradiation with 2×1014 protons/cm2 and 52 days annealing at 20°C. The signal-to-noise ratio measured at −10°C with LHC speed read-out was found to be degraded primarily due to increased noise. The reduction in the reverse current and the changes in the voltage needed for maximum charge collection have both been studied as a function of annealing time. Above the depletion voltage, no effect on the charge collection efficiency has been observed during this annealing period.

Charge collection efficiency of irradiated n+n wedge silicon microstrip detectors for ATLAS

Abstract The charge collection efficiency of the n + n silicon microstrip detectors for the ATLAS forward tracking has been evaluated for detectors irradiated with 24 GeV/c protons. The charge collection efficiency is found to be 99±1% after a fluence of 2×10 14 protons/cm 2 and 81±2% after 4×10 14 protons/cm 2 . Furthermore, the charge collection efficiency of the detector irradiated with the lower dose does not show any dependence on the isothermal annealing up to 52 days at 20°C, as it remains constant through the whole annealing cycle.

ATLAS beam test results

Abstract Many different configurations of electronics and semiconductor strip detectors were studied in 1995 using the ATLAS tracking detector test area at the H8 beam-line of the CERN SPS. A significant fraction of these investigations are presented elsewhere in this volume and this paper will concentrate on the results with silicon strip detectors read out with electronics preserving the pulse height information. Data has been collected with the ADAM, APV5 and FElix read-out chips on a number of different detectors. The first results are presented for read out with LHC electronics of detectors to the ATLAS-A specification of 112.5 μm pitch, employing n-strips in n-type silicon, capacitive coupling and intermediate strips. It is demonstrated that with adequate signal/noise, a spatial resolution of ⋍13 μm is attainable with these detectors.

Radiation hardness of oxygenated microstrip detectors read out with LHC speed electronics

Full-size and miniature Large Hadron Collider (LHC) detectors fabricated on 4- and 6-in wafers have been processed using oxygenated and nonoxygenated substrates. After irradiation to 3/spl times/10/sup 14//cm/sup 2/ with 24-GeV/c protons and short-term annealing, these detectors have been studied in terms of their charge collection as a function of depletion voltage with LHC-speed analog electronics. Results are presented indicating the degree of improvement seen in terms of the main operationally significant parameter, namely, the bias voltage needed for a given signal read out with fast electronics.

Comparison of experimental measurements and electrostatic simulations of keystone geometry microstrip gas chambers

Abstract The developments of MicroStrip Gas Chambers (MSGCs) with non-parallel anodes is a requirement for several proposed pp collider experiments. We have designed and constructed an MSGC with four possible electrode patterns. We report on the measurements of relative gas gain as a function of position along the anodes for each structure and present a comparison of these data with the results of electric field simulations.

The ATLAS SCT grounding and shielding concept and implementation

This paper describes the design and implementation of the grounding and shielding system for the ATLAS SemiConductor Tracker (SCT). The mitigation of electromagnetic interference and noise pickup through power lines is the critical design goal as they have the potential to jeopardize the electrical performance. We accomplish this by adhering to the ATLAS grounding rules, by avoiding ground loops and isolating the different subdetectors. Noise sources are identified and design rules to protect the SCT against them are described. A rigorous implementation of the design was crucial to achieve the required performance. This paper highlights the location, connection and assembly of the different components that affect the grounding and shielding system: cables, filters, cooling pipes, shielding enclosure, power supplies and others. Special care is taken with the electrical properties of materials and joints. The monitoring of the grounding system during the installation period is also discussed. Finally, after connecting more than four thousand SCT modules to all of their services, electrical, mechanical and thermal within the wider ATLAS experimental environment, dedicated tests show that noise pickup is minimised.