120054500
The non-gated charge-to-time converter for TOF detector in BES III
Abstract The TOF (Time-Of-Flight) detector in BES (Beijing Spectrometer) III experiment requires a total time resolution of better than 90 ps (for the barrel part) and 110 ps (for the endcap part). With the requirement of such a high precision time measurement, it is essential to measure the amplitude or charge of the PMT (photomultiplier tube) signals, in order to correct the amplitude dependent time-walk. A method of using non-gated QTC (Charge-to-Time Converter) to measure the input signal charge was developed for BES III TOF readout electronics. The non-gated QTC with differential inputs was designed to measure the input charge covering a dynamic range of about 30–927 pC. Test results showed that the rms resolution is better than 10 bit and the relative error is less than 0.5% after quadratic fitting. The designed converter is simple, stable and suitable for multi-channel systems. A total of 448 channels of QTCs have been developed for BES III TOF readout electronics, which help the TOF system achieve the expected time resolution after the time-walk correction.
33505335
Design of the readout electronics for the Qualification Model of DAMPE BGO calorimeter
The DAMPE (DArk Matter Particle Explorer) is a scientific satellite aimed at cosmic ray study, gamma ray astronomy, and searching for the clue of dark matter particles, with a planned mission period of more than 3 years. The calorimeter, which is composed of 308 BGO (Bismuth Germanate Oxid) crystal bars, is a critical sub-detector for measuring the energy of cosmic particles from 5 GeV to 10TeV, distinguishing positrons/electrons and gamma rays from hadron background, and providing trigger information to the whole payload. In the calorimeter each BGO crystal bar is coupled by two Hamamatsu R5610A PMTs (photomultiplier tubes) from both ends respectively, while each PMT send out signals from three dynodes (2, 5, 8) to cover a large dynamic range from about 11 MeV to 2 TeV for each crystal unit. Thus 616 PMTs and 1848 signal channels are used in the BGO calorimeter. The large amount of detector components and signal channels, as well as large dynamic range requirement, greatly challenge the design of readout electronics, because of the confined area for PCB (Printed Circuit Board) layout and cable layout, the potential crosstalk between high density signal channels especially from dynode 8 to dynode 2, and limited power budget. Besides there are other particular requirements derived from hash space environment, such as good radiation tolerance, high reliability, etc. To conquer above challenges, a serial of methods are taken into the design. Two ASICs with low power consumption, low noise, high dynamic range and high integrity, named VA160 and VATA160, are chosen as the front end chips to read out the charge signal from PMT dynodes, and to provide fast trigger information. The Flash-based FPGA (Field Programmable Gate Array) from Actel ProASIC Plus family is applied, which is considered to be less sensitive to SEU (Single Event Upset) and more power-saving, compared to regular SRAM-based FPGAs. In order to estimate the performances of the ASICs and FPGA chips in radiative space environment, both single event effect (SEE) and total ionizing dose (TID) tests are conducted, and SEU and SEL (Single Event Latch-up) protecting measures are adopted, based on the test results. Right now the DAMPE mission is in QM (Qualification Model) stage, all the readout electronics for the qualification model of BGO calorimeter were successfully designed and produced in the end of year 2013. The DAMPE BGO calorimeter was later integrated at the beginning of 2014 and right now the environmental tests, such as vibration test, thermal cycling and thermal-vacuum test, have been performed. Currently the BGO calorimeter is under integration tests with other sub-detectors, and a beam test will be carried out at CERN, in the autumn of 2014.
140196480
TOF Clock System for BES III
In this paper, a system for providing a precisely timed clock to the time-of-flight (TOF) electronics at Beijing Spectrometer (BES III) is presented. System functions include radio-frequency reference signal transmission and low-jitter clock regeneration and distribution. A new clock synchronizing and monitoring mechanism is developed with off-the-shelf devices to synchronize the clock signal to the beam bunches. The measured short-term jitter performance of the system is 11 ps worst case, and robust synchronization to the beam bunches has also been demonstrated. The system has been installed and is operating reliably.
123771953
A high dynamic range readout unit for a calorimeter
A high dynamic range readout system, consisting of a multi-dynode readout PMT and a VA32 chip, is presented. An LED system is set up to calibrate the relative gains between the dynodes, and the ADC counts per MIPs from dynode 7 are determined under cosmic-ray calibration. A dynamic range from 0.5 MIPs to 1 x 10(5) MIPs is achieved.
39350314
Study on FPGA SEU mitigation for readout electronics of DAMPE BGO calorimeter
The Dark Matter Particle Explorer (DAMPE) is being constructed as a scientific satellite to observe high energy cosmic rays in space. As a main detector of DAMPE, the Bismuth Germanium Oxide (BGO) calorimeter is in charge of measuring particle energy deposition, distinguishing positrons, electrons and gamma rays from hadron background and providing trigger information. The satellite is designed to fly on a near-earth orbit with an altitude of 500km, which makes demands on electronic components for the ability to work in radiation environment.A flash-based Field-Programmable Gate Array (FPGA) of Actel, ProASCI Plus (APA) is chosen as the control component of the Front-End Electronics (FEE). To study the radiation resistance, SEE test was performed at the Heavy Ion Research Facility in Lanzhou (HIRFL). The chip did not exhibit latchup to an effective LET of 90 MeV-cm2/mg. The Flash switches of APA, which provide nonvolatile, reconfigurable interconnect programming and connect routing nets, were immune to SEL. However, SEE experiment also showed that the registers implemented from logic tiles and RAM blocks were SEU sensitive. Therefore, appropriate solutions should be adopted to mitigate SEU effects and make sure that the chip can function well in the radiation environment of space. To achieve maximum SEU tolerance with minimum resource consumption and speed degradation, engineering tradeoffs should be taken into account. Firstly, to the crucial registers and RAMs, Triple Modular Redundancy (TMR) technique is used to ensure that the value after voter is correct and if the values in three modules are different, the voter result will be written back to modules to scrub SEU errors. Besides, the three modules are manually placed in different physical areas to avoid Multiple Bit Upset (MBU). Secondly, CRC checksum is used to check the correctness of configuration data stored in RAM, which can be used as judgment of RAM reconfiguration. And thirdly, the whole logic is divided into four parts with different reset signals, which makes it convenient to set the idle parts into sleep until the external wake-up signals come. After using these means in the logic design, an ion-beam testing is performed to evaluate the SEU tolerance of FPGA logic. The FPGA works well under the condition with the LET of 39.6 MeV-cm2/mg and the ion flux of 100 ions/cm2/s without any mistake. The radiation test verifies that the SEU mitigationstrategies implemented in APA FPGA can meet the space qualification.
137255349
Electronics of BESIII TOF Monitor System
This paper describes the control electronics for the time of flight (TOF) monitor system of BESIII. A 9U VME module is designed as the interface between the TOF monitor laser box and BESIII data acquisition system. It takes charge of enabling the laser source, sending trigger signals to the laser driver, controlling the optic path, and measuring the charge and arrival time of pulses from two reference phototubes. The module also sends a Level 1 trigger to the TOF readout system, after each trigger pulse to the laser source. The interface and control logic are implemented in one Altera field-programmable gate array, and signals from the reference PMTs of the laser system are digitized with the CERN HPTDC technique. A series of experimental tests show that the time resolution of the monitor electronics is better than 25 ps, and the relative methodical error of the charge measurement is less than 0.5% after quadratic fitting. The TOF monitor system was installed at the end of 2007 and has been operating continuously since then. A total time resolution of about 70 ps and a charge resolution of about 4% of the TOF counters have been obtained during field monitor tests.
118830578
Preventing eternality in phantom inflation
We have investigated the necessary conditions that prevent phantom inflation from being eternal. Allowing additionally for a nonminimal coupling between the phantom field and gravity, we present the slow-climb requirements, perform an analysis of the fluctuations, and finally we extract the overall conditions that are necessary in order to prevent eternality. Furthermore, we verify our results by solving explicitly the cosmological equations in a simple example of an exponential potential, formulating the classical motion plus the stochastic effect of the fluctuations through Langevin equations. Our analysis shows that phantom inflation can be finite without the need of additional exotic mechanisms.
119213687
Is cosmological constant needed in Higgs inflation
The detection of B-mode shows a very powerful constraint to theoretical inflation models through the measurement of the tensor-to-scalar ratio r. Higgs boson is the most likely candidate of the inflaton field. But usually, Higgs inflation models predict a small value of r, which is not quite consistent with the recent results from BICEP2. In this paper, we explored whether a cosmological constant energy component is needed to improve the situation. And we found the answer is yes. For the so-called Higgs chaotic inflation model with a quadratic potential, it predicts r approximate to 0.2, n(s) approximate to 0.96 with e-folds number N approximate to 56, which is large enough to overcome the problems such as the horizon problem in the Big Bang cosmology. The required energy scale of the cosmological constant is roughly Lambda similar to (10(14) GeV)(2), which means a mechanism is still needed to solve the fine-tuning problem in the later time evolution of the universe, e.g. by introducing some dark energy component. (C) 2014 The Authors. Published by Elsevier B.V.
119205820
Take up the challenge for a single field inflation after BICEP2
The measurement of the tensor-to-scalar ratio r shows a very powerful constraint to theoretical inflation models through the detection of B-mode. In this paper, we propose a single inflation model with infinity power series potential called the Infinity Power Series (IPS) inflation model, which is well consistent with latest observations from Planck and BICEP2. Furthermore, it is found that in the IPS model, the absolute value running of the spectral index increases while the tensor-to-scalar ratio becomes large, namely both large r approximate to 0.20 and vertical bar n(s)'vertical bar greater than or similar to O(10(-2)) are realized in the IPS model. In the meanwhile, the number of e-folds is also big enough N approximate to 50-60 to solve the problems in Big Bang cosmology.
118416699
Is non-minimal inflation eternal?
Abstract The possibility that the non-minimal coupling inflation could be eternal is investigated. We calculate the quantum fluctuation of the inflaton in a Hubble time and find that it has the same value as that in the minimal case in the slow-roll limit. Armed with this result, we have studied some concrete non-minimal inflationary models including the chaotic inflation and the natural inflation, in which the inflaton is non-minimally coupled to the gravity. We find that the non-minimal coupling inflation could be eternal in some parameter spaces.
119228196
Latest observational constraints to the ghost dark energy model by using the Markov chain Monte Carlo approach
Recently, the vacuum energy of the QCD ghost field in a time-dependent background was proposed as a kind of dark energy candidate called the ghost dark energy model (GDE) to explain the acceleration of the Universe. In this model, the energy density of the dark energy is proportional to the Hubble parameter $H$, which is also regarded as the Hawking temperature on the Hubble horizon of the Friedmann-Robertson-Walker Universe. In this paper, the statefinder and $Om$ diagnostics are applied to the GDE models, and the differences among them are significant during the time of transition. And at that time, the viscosity plays an important role. Furthermore, we find that once the viscosity is taken into account, the age problem of Universe could be alleviated. We also perform a constraint on the GDE models with and without bulk viscosity by using the Markov Chain Monte Carlo method and the combined latest observational data from the type Ia supernova compilations including Union2.1(580) and Union2(557), cosmic microwave background, baryon acoustic oscillation, and the observational Hubble parameter data.