204935814
A new method of waveform digitization based on time-interleaved A/D conversion
Time interleaved analog-to-digital conversion (TIADC) based on parallelism is an effective way to meet the requirement of the ultra-fast waveform digitizer beyond Gsps. Different methods to correct the mismatch errors among different analog-to-digital conversion channels have been developed previously. To overcome the speed limitation in hardware design and to implement the mismatch correction algorithm in real time, this paper proposes a fully parallel correction algorithm. A 12-bit 1-Gsps waveform digitizer with ENOB around 10.5 bit from 5 MHz to 200 MHz is implemented based on the real-time correction algorithm.
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.
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.
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.
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.
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.
118487842
Ricci dark energy in braneworld models with a Gauss-Bonnet term in the bulk
We investigate the Ricci Dark Energy (RDE) in the braneworld models with a Gauss-Bonnet term in the Bulk. We analytically solve the generalized Friedmann equation on the brane and find that the universe will finally enter into a pure de Sitter spacetime in stead of the big rip that appears in the usual 4D Ricci dark energy model with parameter alpha < 1/2. We also consider the Hubble horizon as the IR cutoff in holographic dark energy model and find it cannot accelerate the universe as in the usual case without interacting. (C) 2009 Elsevier B.V. All rights reserved.
118479015
Viscous Ricci dark energy
We investigate the viscous Ricci dark energy (RDE) model by assuming that there is bulk viscosity in the linear barotropic fluid and the RDE. In the RDE model without bulk viscosity, the universe is younger than some old objects at certain redshifts. Since the age of the universe should be longer than any objects living in the universe, the RDE model suffers the age problem, especially when we consider the object APM 08279 + 5255 at z = 3.91 with age t = 2.1 Gyr. In this Letter, we find that once the viscosity is taken into account, this age problem is alleviated. (C) 2009 Elsevier B.V. All rights reserved.
15866726
Reconstructing f (R) theory from Ricci dark energy
In this Letter, we regard the f(R) theory as an effective description for the acceleration of the universe and reconstruct the function f(R) from the Ricci dark energy, which respects holographic principle of quantum gravity. By using different parameter a in RDE, we show the behaviors of reconstructed f(R) and find they are much different in the future. (C) 2009 Published by Elsevier B.V.