07-10-2010, 09:53 AM
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This article is presented by:
M. R. Dutta Majumdar
Debasish Das
Tapan K. Nayak
Variable Energy Cyclotron Centre,
1/AF, Bidhan Nagar, Kolkata - 700064, INDIA
ABSTRACT
Large array gas detector systems are used in particle and nuclear physics experiments involving high-energy nucleon-nucleon and heavy-ion collisions. We have observed that in large array gas detector systems the momentary discharges inside the detector cells result in slowdown of the High Voltage conditioning and possible hindrances in signal processing. We have explored the opto-electronic devices like the opto-coupler, optical fibre and signal processing circuit, which provide successful monitoring procedures and preventive measures to overcome the challenges produced in such complex detector systems.
INTRODUCTION
Large array gas detector systems are widely used in particle and nuclear physics experiments to study and characterize the collision environments in ultra-relativistic nucleon-nucleon and heavy-ion reactions. One of the primary goals of such high-energy heavy-ion experiments is to study the formation and characteristics of the quark-gluon plasma (QGP), a state of matter, which may be created at sufficiently high -energy temperatures and densities. Detecting and understanding the QGP phase will allow us to understand the state of Universe in the mom ents after the Big Bang. Because of the density of produced particles from the collision environment in such reactions is quite high, the gas detectors should be highly segmented or granular to suit for such high multiplicity nuclear physics experiments. Large number of charged particles and photons are produced in high-energy heavy -ion collisions. One of the probes of QGP formation is the measurement of photon multiplicity and spatial distribution of high-energy (~GeV range) photons on an event-by-event basis. The basic principle of photon measurement involves a pre-shower technique using a lead converter and measuring the produced shower particles to characterize the photons. A high-energy photon produces an electromagnetic shower on passing through the converter. These shower particles produce signals in the sensitive volume of the detector. The thickness of the converter is optimised such that the conversion probability of high-energy photons is high and transverse shower spread is small to minimize shower overlap in a high multiplicity environment. The Photon Multiplicity Detectors (PMD) have been successfully used in WA93 and WA98 experiments at CERN, Geneva1, 2 at the CERN Super Proton Synchrotron. The sensitive medium of PMD in these experiments was plastic scintillator pads, which were coupled with Wave Length Shifting (WLS) optical fibres. The signals were read through Charge Coupled Device (CCD) cameras with Image Intensifiers. It consisted of highly segmented detector placed behind a lead converter of suitable thickness. In the ongoing International Collaborations at Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory, USA and the future experiment at the Large Hadron Collider (LHC) at CERN, Geneva we have decided to shift the detector methodology from plastic scintillator to highly segmented gas detectors. The PMD3 presently installed at the STAR experiment at RHIC is a large array gas detector system comprising of 82944 hexagonal honeycomb shaped cellular proportional counters of cross-section 1.0 square cm and gas depth of 0.8 cm. The gas mixture of Ar+CO2 (70:30) is used as the sensitive medium. It has been observed that in large array gas detector systems like PMD, momentary discharges inside the detector cells resulted in the tripping of High Voltage (HV) supply and also causing an occasional damage of signal readout processors. The initial inclusion of opto-electronic devices like the opto-coupler4 provides an additional sensor to monitor such momentary discharges taking place in the gas detector system.
This article is presented by:
M. R. Dutta Majumdar
Debasish Das
Tapan K. Nayak
Variable Energy Cyclotron Centre,
1/AF, Bidhan Nagar, Kolkata - 700064, INDIA
Opto-Electronics in Large Array Gas Detector Systems
ABSTRACT
Large array gas detector systems are used in particle and nuclear physics experiments involving high-energy nucleon-nucleon and heavy-ion collisions. We have observed that in large array gas detector systems the momentary discharges inside the detector cells result in slowdown of the High Voltage conditioning and possible hindrances in signal processing. We have explored the opto-electronic devices like the opto-coupler, optical fibre and signal processing circuit, which provide successful monitoring procedures and preventive measures to overcome the challenges produced in such complex detector systems.
INTRODUCTION
Large array gas detector systems are widely used in particle and nuclear physics experiments to study and characterize the collision environments in ultra-relativistic nucleon-nucleon and heavy-ion reactions. One of the primary goals of such high-energy heavy-ion experiments is to study the formation and characteristics of the quark-gluon plasma (QGP), a state of matter, which may be created at sufficiently high -energy temperatures and densities. Detecting and understanding the QGP phase will allow us to understand the state of Universe in the mom ents after the Big Bang. Because of the density of produced particles from the collision environment in such reactions is quite high, the gas detectors should be highly segmented or granular to suit for such high multiplicity nuclear physics experiments. Large number of charged particles and photons are produced in high-energy heavy -ion collisions. One of the probes of QGP formation is the measurement of photon multiplicity and spatial distribution of high-energy (~GeV range) photons on an event-by-event basis. The basic principle of photon measurement involves a pre-shower technique using a lead converter and measuring the produced shower particles to characterize the photons. A high-energy photon produces an electromagnetic shower on passing through the converter. These shower particles produce signals in the sensitive volume of the detector. The thickness of the converter is optimised such that the conversion probability of high-energy photons is high and transverse shower spread is small to minimize shower overlap in a high multiplicity environment. The Photon Multiplicity Detectors (PMD) have been successfully used in WA93 and WA98 experiments at CERN, Geneva1, 2 at the CERN Super Proton Synchrotron. The sensitive medium of PMD in these experiments was plastic scintillator pads, which were coupled with Wave Length Shifting (WLS) optical fibres. The signals were read through Charge Coupled Device (CCD) cameras with Image Intensifiers. It consisted of highly segmented detector placed behind a lead converter of suitable thickness. In the ongoing International Collaborations at Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory, USA and the future experiment at the Large Hadron Collider (LHC) at CERN, Geneva we have decided to shift the detector methodology from plastic scintillator to highly segmented gas detectors. The PMD3 presently installed at the STAR experiment at RHIC is a large array gas detector system comprising of 82944 hexagonal honeycomb shaped cellular proportional counters of cross-section 1.0 square cm and gas depth of 0.8 cm. The gas mixture of Ar+CO2 (70:30) is used as the sensitive medium. It has been observed that in large array gas detector systems like PMD, momentary discharges inside the detector cells resulted in the tripping of High Voltage (HV) supply and also causing an occasional damage of signal readout processors. The initial inclusion of opto-electronic devices like the opto-coupler4 provides an additional sensor to monitor such momentary discharges taking place in the gas detector system.