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Added by
Frederick A. Harris
Publication date
2008
fields
Physics
and research's language is
English
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A Time of Flight monitoring system has been developed for BES3. The light source is a 442-443 nm laser diode, which is stable and provides a pulse width as narrow as 50 ps and a peak power as large as 2.6 W. Two optical-fiber bundles with a total of 512 optical fibers, including spares, are used to distribute the light pulses to the Time of Flight counters. The design, operation, and performance of the system are described.
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The Compressed Baryonic Matter spectrometer (CBM) is a future fixed-target heavy-ion experiment located at the Facility for Anti-proton and Ion Research (FAIR) in Darmstadt, Germany. The key element in CBM providing hadron identification at incident beam energies between 2 and 11 AGeV (for Au-nuclei) will be a 120 m$^2$ large Time-of-Flight (ToF) wall composed of Multi-gap Resistive Plate Chambers (MRPC) with a system time resolution better than 80 ps. Aiming for an interaction rate of 10 MHz for Au+Au collisions the MRPCs have to cope with an incident particle flux between 0.1~kHz/cm$^2$ and 100~kHz/cm$^2$ depending on their location. Characterized by granularity and rate capability the actual conceptual design of the ToF-wall foresees 6 different counter granularities and 4 different counter designs. In order to elaborate the final MRPC design of these counters several heavy-ion in-beam and cosmic tests were performed. In this contribution we present the conceptual design of the TOF wall and in particular discuss performance results of full-size MRPC prototypes.
A laser calibration system was developed for monitoring and calibrating time of flight (TOF) scintillating detector arrays. The system includes setups for both small- and large-scale scintillator arrays. Following test-bench characterization, the laser system was recently commissioned in experimental Hall B at the Thomas Jefferson National Accelerator Facility for use on the new Backward Angle Neutron Detector (BAND) scintillator array. The system successfully provided time walk corrections, absolute time calibration, and TOF drift correction for the scintillators in BAND. This showcases the general applicability of the system for use on high-precision TOF detectors.
In the MICE experiment at RAL the upstream time-of-flight detectors are used for particle identification in the incoming muon beam, for the experiment trigger and for a precise timing (sigma_t ~ 50 ps) with respect to the accelerating RF cavities working at 201 MHz. The construction of the upstream section of the MICE time-of-flight system and the tests done to characterize its individual components are shown. Detector timing resolutions ~50-60 ps were achieved. Test beam performance and preliminary results obtained with beam at RAL are reported.
A system based on commercially available items, such as a laser diode, emitting in the visible range $sim 400$ nm,and multimode fiber patches, fused fiber splitters and optical switches may be assembled,for time calibration of multi-channels time-of-flight (TOF) detectors with photomultipliers (PMTs) readout. As available laser diode sources have unfortunately limited peak power, the main experimental problem is the tight light power budget of such a system. In addition, while the technology for fused fiber splitters is common in the Telecom wavelength range ($lambda sim 850, 1300-1500$ nm), it is not easily available in the visible one. Therefore, extensive laboratory tests had to be done on purpose, to qualify the used optical components, and a full scale timing calibration prototype was built. Obtained results show that with such a system, a calibration resolution ($sigma$) in the range 20-30 ps may be within reach. Therefore, fast multi-channels TOF detectors, with timing resolutions in the range 50-100 ps, may be easily calibrated in time. Results on tested optical components may be of interest also for time calibration of different light detection systems based on PMTs, as the ones used for detection of the vacuum ultraviolet scintillation light emitted by ionizing particles in large LAr TPCs.
The Time-Of-Flight system consisting of plastic scintillation counters plays an important role for particle identification in the BESIII experiment at the BEPCII double ring $e^+e^-$ collider. Degradation of the detection efficiency of the barrel TOF system has been observed since the start of physical data taking and this effect has triggered intensive and systematic studies about aging effects of the detector. The aging rates of the attenuation lengths and relative gains are obtained based on the data acquired in past several years. This study is essential for ensuring an extended operation of the barrel TOF system in optimal conditions.
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