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.
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.
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.
119116661
Global behavior of cosmological dynamics with interacting Veneziano ghost
A bstractIn this paper, we shall study the dynamical behavior of the universe accelerated by the so called Veneziano ghost dark energy component locally and globally by using the linearization and nullcline method developed in this paper. The energy density is generalized to be proportional to the Hawking temperature defined on the trapping horizon instead of Hubble horizon of the Friedmann-Robertson-Walker (FRW) universe. We also give a prediction of the fate of the universe and present the bifurcation phenomenon of the dynamical system of the universe. It seems that the universe could be dominated by dark energy at present in some region of the parameter space.
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.
15412072
Chaplygin gas and the cosmological evolution of alpha
The class of Chaplygin gas models regarded as a candidate of dark energy can be realized by a scalar field, which could drive the variation of the fine structure constant $\alpha$ during the cosmic time. This phenomenon has been observed for almost ten years ago from the quasar absorption spectra and attracted many attentions. In this paper, we reconstruct the class of Chaplygin gas models to a kind of scalar fields and confront the resulting $\Delta\alpha/\alpha$ with the observational constraints. We found that if the present observational value of the equation of state of the dark energy was not exactly equal to -1, various parameters of the class of Chaplygin gas models are allowed to satisfy the observational constraints, as well as the equivalence principle is also respected.
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.
118416483
Bifurcation and global dynamical behavior of the f(T) theory
Usually, in order to investigate the evolution of a theory, one may find the critical points of the system and then perform perturbations around these critical points to see whether they are stable or not. This local method is very useful when the initial values of the dynamical variables are not far away from the critical points. Essentially, the nonlinear effects are totally neglected in such kind of approach. Therefore, one cannot tell whether the dynamical system will evolute to the stable critical points or not when the initial values of the variables do not dose enough to these critical points. Furthermore, when there are two or more stable critical points in the system, local analysis cannot provide the information on which the system will finally evolute to. In this paper, we have further developed the nullcline method to study the bifurcation phenomenon and global dynamical behavior of the f(T) theory. We overcome the shortcoming of local analysis. And, it is very clear to see the evolution of the system under any initial conditions.