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.
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.
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.
30938289
A high density time to digital converter module for BESIII end-cap TOF upgrade
This paper describes the high precision time measurement for the end-cap time of flight (ETOF) upgrade of a Beijing Spectrometer (BESIII). After upgrade, ETOF will be built using Multigap Resistive Plate Chambers (MRPC) and will have 1728 readout channels which is a big challenge for the readout electronics. The time resolution of the readout electronics system is required to be better than 25 ps. A 9U VME module with 72 time measurement channels is designed to perform particles flight time measurement. The signals, which are produced by the detector and then amplified and discriminated by the frontend electronics, are sent to the time-to-digital converter (TDIG) module to be digitized. The TDIG module uses the CERN HPTDC technique to achieve high precision time-to-digital converter and totally applies nine HPTDC chips to realize 72 channels. The primary hit measurements from HPTDC chips are forwarded to one Altera field-programmable gate array (FPGA) to be processed. Finally, the data are sent to DAQ server by Ethernet. The VME interface logic is implemented in an Altera CPLD. The TDIG module can also accept an external trigger and pick out the expected events which are correlated with the given trigger. A series of experiment tests show that the time resolution of the TDIG module is better than 20 ps.
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.
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.
15618257
Reheating and Cosmic String Production
Abstract We compute the string production rate at the end of inflation, using the string spectrum obtained in [M. Li, W. Song, Y. Song, Quantizing strings in de Sitter space, JHEP 0704 (2007) 042, hep-th/0701258 ] in a near-de Sitter space. Our result shows that highly excited strings are hardly produced, thus the simple slow-roll inflation alone does not offer a cosmic string production mechanism.
118846731
Note on Power-Law Inflation in Noncommutative Space-Time
In this paper, we propose a new method to calculate the mode functions in the noncommutative power-law inflation model. In this model, all the modes created when the stringy space-time uncertainty relation is satisfied are generated inside the Hubble horizon during inflation. It turns out that a linear term describing the noncommutative space-time effect contributes to the power spectra of the scalar and tensor perturbations. Confronting this model with latest results from \textit{Planck} and BICEP2, we constrain the parameters in this model and we find it is well consistent with observations.
118367913
Scalar perturbation and stability of Ricci dark energy
The Ricci dark energy (RDE) proposed to explain the accelerating expansion of the universe requires its parameter alpha 1/3, which gives a lower bound for alpha theoretically. (C) 2009 Elsevier B.V. All rights reserved.
119115314
CASIMIR EFFECT UNDER QUASI-PERIODIC BOUNDARY CONDITION INSPIRED BY NANOTUBES
When one studies the Casimir effect, the periodic (anti-periodic) boundary condition is usually taken to mimic a periodic (anti-periodic) structure for a scalar field living in a flat space with a non-Euclidean topology. However, there could be an arbitrary phase difference between the value of the scalar field on one endpoint of the unit structure and that on the other endpoint, such as the structure of nanotubes. Then, in this paper, a periodic condition on the ends of the system with an additional phase factor, which is called the "quasi-periodic" condition, is imposed to investigate the corresponding Casimir effect. And an attractive or repulsive Casimir force is found, whose properties depend on the phase angle value. Especially, the Casimir effect disappears when the phase angle takes a particular value. High dimensional spacetime case is also investigated.
16041279
Holographic Cosmological Constant and Dark Energy
A general holographic relation between UV and IR cutoff of an effective field theory is proposed. Taking the IR cutoff relevant to the dark energy as the Hubble scale, we find that the cosmological constant is highly suppressed by a numerical factor and the fine tuning problem seems alleviative. We also use different IR cutoffs to study the case in which the universe is composed of matter and dark energy.