Improving the timing resolution of an electromagnetic calorimeter based on lead tungstate crystals

Results of the beam tests of the prototype photon spectrometer PHOS for the ALICE experiment at the Large Hadron Collider (CERN) are presented. The spectrometer is based on detector elements composed of lead tungstate (PbWO₄) crystals with dimensions of 22 × 22 × 180 mm and Hamamatsu S8664-55 (S8148) avalanche photodiodes. The beam tests have been performed on the secondary T10 beamline of the PS proton synchrotron. The main emphasis has been placed on the possibility of improving the PHOS timing resolution. Introduction of an additional timing channel with a silicon photomultiplier (SiPM) used as a photodetector is shown to improve the timing resolution for 1-GeV deposited energy from current value σ _t = 3 to 0.3 ns. Silicon photomultipliers of the Hamamatsu MPPC S10362-33 family with an active area of 3 × 3 mm² are used in these measurements. Using fast photomultiplier tubes with an 8-mm-diameter photocathode, the timing resolution attainable in electromagnetic shower development in a lead tungstate crystal has been measured for a large-area photodetector. The timing resolution for a deposited energy of 1 GeV is 150 ps. The effect of the detector channel temperature on the timing resolution is investigated. Cooling the crystal results in an increase both in the scintillation intensity and in the decay time of the scintillator and fails to substantially improve the timing resolution.     

The use of silicon photomultipliers for improving the time resolution of an electromagnetic calorimeter based on lead tungstate crystals

The use of S12572 MPPC silicon photomultipliers (Hamamatsu) for improving the timing characteristics of the PHOS electromagnetic calorimeter in the ALICE experiment at CERN is described. It is shown that by introducing an additional photodetector, that is, a silicon photomultiplier, it is possible, without worsening the energy resolution, to significantly improve the time resolution of the PHOS spectrometer from the current values of 3–4 ns to 150–200 ps.     

Time characteristics of detectors based on silicon photomultipliers for the GlueX experiment

Silicon photomultipliers (SiPMs) are used in detectors of the GlueX experiment devoted to studying the nature of confinement. These detectors are operable at counting rates as high as 2 MHz with a time resolution (FWHM) of approximately 0.3 ns and a number of excited pixels of up to 10⁴. For SiPMs that operate under these conditions, the measured dependences of the recovery time and the time resolution are presented as functions of the number of excited pixels and the excitation frequency. Using a picosecond laser, the time resolution has been measured for an array of 4 × 4 SiPMs, which was specially developed for the experiment.     

Development of the Readout and Data-Acquisition System for the RICH Detector of the CBM Experiment

A 64-channel readout and data-acquisition module is described in detail. It consists of an H12700 multianode photomultiplier tube, four PADIWA preamplifier boards, and a TRB v3 card that perform the functions of a time-to-digital converter and a data concentrator. The software modules that are necessary for operation of the prototype are described. The inter-channel delays are calibrated. The drift of individual delays does not exceed 0.5 ns for the entire measurement time. The spectra of the “time over threshold” (ToT) are investigated. The influence of periodic noise pickups and the need to improve circuit designs are revealed. The timing properties of the wavelength shifter and its effect on the detection efficiency for Cherenkov rings are investigated. The most intense component is characterized by a decay time of 1.1 ns and there are components with characteristic times of 3.8 and 45 ns. The influence of single-electron spectrum features on the detection efficiency for photoelectrons and the probability of false hits are determined. The total time resolution of 131 channels is 1.1 ns (FWHM). The results make it possible to use the investigated system of readout and data acquisition in the CBM experiment. Nevertheless, the elimination of the revealed shortcomings will provide the efficiency margin and improve the reliability of the system during long-term operation.     

Reflection-time-of-flight spectrometer for two-electron (e,2e) coincidence spectroscopy on surfaces

In this article, a novel time-of-flight spectrometer for two-electron-emission (e,2egamma,2e) correlation spectroscopy from surfaces at low electron energies is presented. The spectrometer consists of electron optics that collect emitted electrons over a solid angle of approximately 1 sr and focus them onto a multichannel plate using a reflection technique. The flight time of an electron with kinetic energy of Ekin approximately 25 eV is around 100 ns. The corresponding time- and energy resolution are typically approximately 1 ns and approximately 0.65 eV, respectively. The first (e,2e) data obtained with the present setup from a LiF film are presented.     

Extraction of the carbon ion beam from the U-70 accelerator into beamline 4a using a bent single crystal

A beam of six-charged carbon ions with an energy of 24.8 GeV/nucleon is extracted from the U-70 synchrotron by means of a silicon crystal bent through 85 mrad. A total of 200000 particles are observed in beamline 4a upon forcing 10⁹ circulating ions to the crystal. The geometrical parameters, timing structure, and composition of the beam have been measured. It has been shown for the first time that, using a bent single crystal, an ion beam with required parameters can be extracted from the accelerator ring and formed for regular use in physics experiments.     

A discriminator with digital correction for upgrading the T0 detector of the ALICE experiment

A discriminator with digital correction (DWDC) with a dead time of 25 ns or less and a time resolution of 50 ps or better is intended for upgrading the data acquisition system of the T0 start trigger detector (ALICE—A Large Ion Collider Experiment on the Large Hadron Collider).     

Use of a Dielectric as a Sensitive Element of an X-Ray Detector

An X-ray detector with a dielectric (KU1 optical glass) used as a sensitive element is described. Operation of the detector is based on the discovered effect of electric-field generation in a dielectric under exposure to radiation. The measurements were taken at the Angara-5-1 facility, at which the radiation source is megaampere Z-pinch plasma. It is shown that when the radiation power incident on the detector is approximately 1 MW/cm², the detector response is a few volts with a time resolution of 1–2 ns. This effect is thought to be caused by “hot” electrons induced by radiation in the dielectric. The estimates for these experimental conditions are presented.     

A Stroboscopic Photorecorder

A stroboscopic photorecorder (SP) with a wideband external modulator of the photomultiplier current and manufactured on the basis of a commercial sampling oscilloscope is described. The time resolution of the SP with an C7-16 computing oscilloscope is 0.47 ns; this value corresponds to the rise time of the oscilloscope transient response (0.45 ns). The circuit diagram for connecting the C7-16 oscilloscope to the SP units is presented. The application of a standard sampling oscilloscope substantially reduces the time and laboriousness of SP assembly and ensures high performance characteristics (quantum sensitivity, linearity of gain, and time resolution).     

Multiwavelength optical pyrometer for shock compression experiments

A system for measurement of the spectral radiance of materials shocked to high pressures ( approximately 100 GPa) by impact using a light gas gun is described. Thermal radiation from the sample is sampled at six wavelength bands in the visible spectrum, and each signal is separately detected by solid-state photodiodes, and recorded with a time resolution of approximately 10 ns. Interpretation of the records in terms of temperature of transparent sample materials is discussed. Results of a series of exploratory experiments with metals are also given. Shock temperatures in the range 4000-8000 K have been reliably measured. Spectral radiance and temperatures have been determined with uncertainties of 2%.     

接收机位置误差对GNSS定时的影响分析

不准确的接收机位置信息将会影响用户的定时结果。从理论推导和试验两方面研究了接收机位置误差对定时结果的影响。首先理论上通过对伪距观测方程求一阶微分推导得出定时接收机位置误差对定时的最大影响量;为排除卫星位置误差的影响,利用IGS提供的卫星精确位置,通过引入不同量级的接收机位置误差开展试验,对理论分析结果进行了验证;再通过接收机坐标置偏试验分析不同方向置偏不同量级的位置误差下GPS/GLONASS接收机的观测数据,分析了实际运行环境中的位置误差对接收机定时结果的影响。试验结果表明接收机的纬度、经度分量误差均会对定时结果的准确度和稳定度产生影响,纬度误差每增大1″,对GPS和GLONASS定时准确度的影响分别小于5、15 ns,对稳定度的影响分别小于10和15 ns;经度误差每增大1″,对GPS和GLONASS准确度的影响均小于1 ns,对稳定度的影响均小于10 ns;高程坐标分量误差每增加1 m,会出现约3 ns的定时偏差,对定时稳定度的影响则最大约0.3 ns/m。在实际应用中,用户可参考本文的结论根据所需定时精度的需求,考虑定时接收机输入坐标的精确度。     

A Time-to-Code Converter with a Selection of Time Intervals by Duration

A time-to-code converter with preliminary selection of measured time intervals by duration is described. The intervals are selected with the use of Analog Devices programmable delay generators. The selection time of the measured time intervals is 50 ns, the conversion range is from 0 to 100 ns, and the resolution is 0.1 ns.     

Test of prototype hadron calorimeter for the L3 experiment

A fine sampling, tracking hadron calorimeter operating with limited streamer tubes and using a copper absorber has been tested with pions from 1 to 10 GeV/c. The energy resolution measured is consistent with the one expected from empirical formulae obtained for scintillator calorimeters, thus demonstrating that streamer tubes bring little or no loss in resolution. Our laboratory tests have demonstrated that chambers using tubes as small as 3.5 × 4.5 mm² can operate satisfactorily in limited streamer mode.     

An Electromagnetic Calorimeter with a Transversal Orientation of the Scintillating Fibers

The space and energy resolutions of the SPACAL electromagnetic calorimeter with a transverse orientation of the scintillating fibers have been measured. The main parameters of the calorimeter are presented. The results of experiments with an electron test beam of the DESY synchrotron at energies E = 1–6 GeV are discussed. The measured energy resolution of the calorimeter is found to be (/E) = 12.7%/E 2.0% (E is expressed in terms of GeV), and the space resolution is _{x, y} (E) = 1 mm at E = 4 GeV.     

Five-frame, x-ray camera for charged particle, inertial confinement fusion studies

A prototype framing x-ray camera has been developed for photographic studies of inertial confinement fusion (ICF) targets irradiated by charged particle beams. Electron images from five, independently gated, microchannel plates are transported out of the radiation field by means of a toroidal magnetic field and are permanently recorded on film. The calculated, effective exposure time is 相似文献   

A beam-position monitor system at the VEPP-4M electron−positron collider

The VEPP-4M storage ring has been designed for experiments with colliding electron?positron beams, a synchrotron radiation beam, and extracted γ-ray beams at energies of 1?5 GeV. A correct equilibrium beam orbit must be kept in the storage ring to maintain the required experimental conditions. A beam position monitor system is used for this purpose. It includes 54 beam position monitors, monitor signal-processing modules, and synch signals distributors. In 2013–2016, new signal processing modules with a high time resolution were developed and installed at the VEPP-4M storage ring. These have two main advantages over the old modules. First, the new modules allow separate position measurements of electron and positron bunches at an interval between the bunch signals as long as 18 ns. Second, they are able to perform fullfledged turn-by-turn beam position measurements, which is very important for adjustment of the storagering parameters. Turn-by-turn beam position measurements can be performed during injection of a new beam, beam kicking, beam loss, or at an arbitrary instant of time. The structures and main features of the new modules are described, the measurement accuracy is analyzed, and some results of their operation at the storage ring are presented.     

Large area mass analyzer instrument for the chemical analysis of interstellar dust particles

A new instrument to analyze the chemical composition of dust particles in situ in space has been developed. The large target area ( approximately 0.2 m(2)) makes this instrument well suited for detecting a statistically significant number of interstellar dust grains or other dust particles with a low flux. The device is a reflectron-type time-of-flight mass spectrometer that uses only flat electrodes for the generation of the parabolic potential. The instrument analyzes the ions from the impact generated plasma due to hypervelocity dust impacts onto a solid target surface. The SIMION ion optics software package is used to investigate different potential field configurations and optimize the mass resolution and focusing of the ions. The cylindrically symmetric instrument operates with six ring electrodes and six annular electrodes biased to different potentials to create the potential distribution of the reflectron. The laboratory model of the instrument has been fabricated and tested. Hypervelocity dust impacts are simulated by laser ablation using a frequency doubled Nd:YAG laser with approximately 8 ns pulse length. The experimental data show typical mass resolution m/Deltam approximately 200.     

A study of the time and amplitude characteristics of the scintillation counter two meters long with ΦЭУ-115M photomultiplier tubes

The time and amplitude characteristics of a scintillation counter were investigated on an accelerator beam with a momentum of 5 GeV/c at the Institute for High Energy Physics. The scintillator, with a length of 2 m and a cross section of 2.5 × 2.5 cm², was viewed from its end faces by ΦЭУ-115M photomultiplier tubes (PMTs). The dependences of the signal amplitude and the time resolution of a PMT on the position of a particle track along the scintillator were described by quadratic exponentials. When a constant fraction discriminator was used to form the PMT signal, the time resolutions at the center and at the periphery of the counter were 150 and 80 ps, respectively. Better results were obtained with a standard leading-edge discriminator after correcting the dependence of its response time on the signal amplitude.     

A Neutron Spectrometer for Experiments with Radioactive Beams on the ACCULINNA-2 Fragment Separator

A neutron spectrometer based on stilbene crystals has been developed by the Flerov Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research (Dubna, Russia). The timing resolution is determined as a function of the signal amplitude (σT = 0.18 ns at an amplitude of 1 MeV in the electron equivalent). The measured energy resolution of the detecting modules for γ rays is σE/E = 4.5% at E = 1 MeV. The quality of the n–γ discrimination is investigated. It is shown that reliable discrimination is possible, beginning with a deposited energy of 100 keV in the electron equivalent, which corresponds to the kinetic energy of recoil protons of ～700 keV. The neutron spectrometer helps to significantly expand the experimental capabilities and to carry out correlation experiments with radioactive beams on the ACCULINNA-2 fragment separator at a new level of quality.     

Use of an CXP8 X-ray streak camera for measuring the time characteristics of X rays emitted by a laser plasma

The time dependence of the X-ray intensity from targets exposed to single-shot or successive picosecond laser pulses at the NEODIM facility was obtained by direct measurements. The measurements were taken using an CXP8 streak camera (produced by the Research Institute of Pulse Techniques) with a picosecond time resolution under different operating conditions of the facility. The observed X-ray pulses had a half-height duration of 15–50 ps and a rise time of 5 ps at a ∼1.5-ps duration of the effecting laser pulse. Under actual experimental conditions, it was ascertained that time dependences of the X-ray intensity could be recorded for more than 200 spatial elements on a single record at a sweep duration of 0.5 ns per frame and a time resolution of <5 ps.