Beam trip diagnostic system at SSRF

In this paper we report the design and realization of beam trip diagnostic system at Shanghai Synchrotron Radiation Facility (SSRF).The system can find out the first fault signal in the key operation signals related to the RF system by analyzing the time sequence,also it can decide which trips occurs first among the three superconducting RF stations.All the states of monitored signals in a time period ahead and behind beam trip are recorded.The results are compared with those from other diagnostic tools at SSRF.The work is of help in improving reliability of the superconducting RF system and stability of the storage ring operation.     

合肥光源谐波法束团长度测量系统研制

同步辐射光与束流信号具有相同的时间结构,测量同步辐射光并基于频域的信号处理方法可得到束团的长度。基于该原理,研制了采用谐波法测量束团长度的系统。该系统用高速光电接收器将同步光转换为电信号,然后采集该信号的四路频率分量,计算得到束团长度。阐述了该系统的软硬件设计,并应用该系统测量了束团长度随流强的变化规律,与条纹相机的测量结果相吻合。     

Numerical analysis of startup PWR with fractional neutron point kinetic equation

In this paper we present the numerical analysis of the neutron density behavior when the nuclear reactor power is increased during startup of a PWR. The fractional neutron point kinetic (FNPK) equation with one-group delayed neutron precursor and external neutron source was used for this analysis. It is considered that there is a relaxation time associated with a rapid variation in the neutron flux and this effect is considered with the FNPK which have a physical interpretation of the fractional order is related with the sub-diffusive process, i.e., non-Fickian effects from the neutron diffusion equation point of view. In order to study the relaxation time effects during start-up of a PWR, a numerical analysis with FNPK is carried out, which it is assumed that during the ith step of control rod withdrawal the way of reactivity insertion is step to step, where the neutron source strength was defined as a constant in terms of a known initial stable sub-criticality and the neutron signal from a steady state condition. The results of the FNPK were compared with the classical neutron point kinetics (CNPK), for different values of the anomalous relaxation time.     

基于S-K数字成形和种群技术的脉冲参数提取方法

核脉冲信号成形前的指数信号往往含有较为丰富的高频信号并叠加有噪音,使指数信号的参数识别变得困难,对此,本文提出一种通过成形后的信号反推成形前参数的方法。采用S-K高斯数字成形算法和种群技术,由高斯信号搜寻指数信号的参数。结果表明,该方法得到的指数脉冲参数精度高:幅值和产生时间误差在1%以内,时间常数误差为2%左右,是一种性能良好的脉冲识别方法。     

A study on technique to estimate impact location of loose part using Wigner-Ville distribution

Presented in this paper is a method to estimate impact location of a loose part using the Wigner-Ville distribution. The method uses dispersion characteristics of bending waves propagated in a plate. The power propagation velocity and arrival time difference of bending waves related to the dispersion characteristics can be obtained through the transformation of impact signals using the Wigner-Ville distribution. The distance from the impact location to the signal measuring point can be estimated using the information on the power propagation velocity and the arrival time difference of two bending waves. The experimental results show that the proposed method estimates the impact location with relative percentage error within 10% compared with the actual impact location.     

Determination of Charge Sensitivity of a Tunnel Diode Voltage Threshold Discriminator Used in Time Difference Measurements

The results of an investigation of the delay time variation of a tunnel diode (TD) threshold sensing discriminator are presented. These variations are a function of the square root of the input signal risetime and are accountable in terms of a charge sensitivity of the tunnel diode. A distinction is made between the charge sensitivity due to continuously rising signals and that due to short low energy pulses. A simple experimental method used for measuring the delay time variation as a function of the input signal risetime is described. The method is quite general and may be applied to any type of threshold discriminator. A theoretical model of the tunnel diode operating in the discriminator mode is developed. An equivalent circuit approach is used in this development by considering three phases of operation; before the TD reaches threshold, during the actual TD switching, and after the TD has fired. The model agrees with the experimental data, and it is concluded that the charge sensitivity model is a usefully valid concept which is applicable to the design and prediction of discriminator time-delay characteristics.     

Non-linear dynamics of a two phase flow system in an evaporator: The effects of (i) a time varying pressure drop (ii) an axially varying heat flux

In this paper we study the phenomena of density wave oscillations (DWO) in a vertical heated channel. The homogeneous equilibrium model is used to simulate the flow in the two-phase region. The equations are solved numerically using a ‘shooting-method' technique. This in its turn employs an implicit backward finite difference scheme. The scheme can incorporate the movement of the interface. It is very elegant and does not involve storage of variables in large N×N matrices. This scheme is sufficiently general and can be used to simulate the dynamic behaviour when: (i) the heat flux imposed at the surface is non-constant, i.e. exhibits an axial variation; and (ii) the imposed pressure drop is varied periodically at a fixed frequency. A possible explanation for the conflicting reports of the effect of a periodic variation in heat flux is provided using a linear stability analysis and the D-partition method. The interaction of the natural frequency of the DWO and the fixed forcing frequency of the imposed pressure drop gives rise to various phenomena viz relaxation oscillations, sub-harmonic oscillations, quasi-periodic and chaotic solutions. To aid the experimentalist describe this infinite-dimensional system on the basis of his experimental results we discuss the characterisation using only the velocity time series data. This is done employing the method of delay coordinate embedding. The phase portraits, stroboscopic map and correlation dimension of the actual attractor are compared with that of the reconstructed attractor from the velocity time series.     

核信号数值仿真方法的研究及应用

提出并建立了一种数值仿真方法,通过计算机模拟,生成各种数字化核信号波形,以此作为工具开展核信号数字处理方法的研究.通过准高斯滤波、梯形滤波和匹配滤波算法对数字核信号处理结果的研究与比较表明,提出的方法是准确而可行的.     

Charge transfer efficiency in proton damaged CCD's

We have performed detailed measurements of the charge transfer efficiency (CTE) in a thinned, backside-illuminated imaging charge-coupled device (CCD). The device had been damaged in three separate sections by proton radiation typical of that which a CCD would receive in space-borne experiments, nuclear imaging, or particle detection. We examined CTE as a function of signal level, temperature, and radiation dose. The dominant factor affecting the CTE in radiation-damaged CCD's is seen to be trapping by bulk states. We present a simple physical model for trapping as a function of transfer rate, trap concentration, and temperature. We have made calculations using this model and arrived at predictions which closely match the measured results. The CTE was also observed to have a nonlinear dependence on signal level. Using two-dimensional device simulations to examine the distribution of the charge packets in the CCD channel over a range of signal levels, we were able to explain the observed variation     

行波电子直线加速器稳频系统的鉴频方法

稳频系统的频率稳定度取决于谐振腔体的有载品质因素。因电子直线加速器的功率源是脉冲磁控管，其功率谱为形状，无限增大品质因素是不正确的，由帕息维尔定理知道腔体平方律检波器输出信号的面积正比于腔体输出能量，于是当磁控管振荡频率改变时，该信号面积的变化等效于腔体输出能量的变化，根据上述原理获得了品质因素的上限和推荐表达式。     

Modern methods of signal processing in the loose part monitoring system

The loose part monitoring system (LPMS) in the primary circuit of the WWER-440/WWER-1000 as in any other PWR or BWR type of NPP is one of the fundamental and essential to safety diagnostic tools. The purpose of the system is to detect, localize and analyze detached or loose metal pieces. When the metal impact occurs it causes the mechanical vibration of the structures and sensors detect a burst signal. The aim of this work is to show the potential of using modern signal processing methods in enhancing the LPMS performance by solving the tasks of noise cancellation, time of arrival detection, discrimination between real and faulty alarms, and loose metal piece mass estimation.     

n-γ核信号的matlab仿真及其数字波形甄别方法研究

由于中子射线中常常混有γ射线,所以在探测器探测到中子信号的同时也可能会探测到γ信号,而对不同的核信号进行区分具有重大意义。本文利用 matlab 软件开展了中子和γ粒子数字化核信号波形仿真研究,并利用几种核脉冲波形甄别方法对仿真波形进行甄别,最后对不同方法的甄别效果展开了分析讨论。结果表明,电荷比较法、上升时间法和脉冲梯度分析法都是稳定的甄别方法,可有效实现n-γ甄别,其中电荷比较法的甄别效果相对较好。     

nGγ核信号的matlab仿真及其数字波形甄别方法研究

由于中子射线中常常混有γ射线,所以在探测器探测到中子信号的同时也可能会探测到γ信号,而对不同的核信号进行区分具有重大意义。本文利用 matlab 软件开展了中子和γ粒子数字化核信号波形仿真研究,并利用几种核脉冲波形甄别方法对仿真波形进行甄别,最后对不同方法的甄别效果展开了分析讨论。结果表明,电荷比较法、上升时间法和脉冲梯度分析法都是稳定的甄别方法,可有效实现n-γ甄别,其中电荷比较法的甄别效果相对较好。     

Development of Reactor Noise Monitor

A reactor noise monitor has been developed to provide a tool that serves the real time routine function of detecting anomalous states of operation in power reactors. In this monitor, RMS (root mean square) values and average frequencies of noise signals are calculated on a real time basis. The average frequency is defined as the frequency averaged by weighting with PSD (power spectral density) of the noise signal and proved to be equivalent to the ratio of an RMS value of the differentiated noise signal to an RMS value of the noise signal itself. Thus, the average frequency can be obtained on a real time basis by using a differentiator, an RMS calculator and a divider. The frequency components of 12 kinds of signals ranging of 0.01–36 Hz are divided into two or three frequency regions by band-pass filters and the RMS value and the average frequency of each frequency region are obtained by the digital calculation method. The performance of this monitor was tested by using a simulated anomalous signal with a peak on its PSD. From the test, it is proved that this monitor can detect more than changes of the RMS value and average frequency. The functions of this monitor were also confirmed at the actual BWR power plant.

In addition, a method to detect peak location of PSD is developed and the accuracy of the peak frequency measurement of the proposed method is investigated to be satisfactory.     

A nodal modal method for the neutron diffusion equation. Application to BWR instabilities analysis

Fast codes, capable of dealing with three-dimensional geometries, are needed to be able to simulate spatially complicated transients in a nuclear power reactor. In this paper, we propose a modal method to integrate the neutron diffusion equation in which the spatial part has been previously dicretized using a nodal collocation method. For the time integration of the resulting system of differential equations it is supposed that the solution can be expanded as a linear combination of the dominant Lambda modes associated with a static configuration of the reactor core and, using the eigenfunctions of the adjoint problem, a system of differential equations of lower dimension is obtained. This system is integrated using a variable time step implicit method. Furthermore, for realistic transients, it would be necessary to calculate a large amount of modes. To avoid this, the modal method has been implemented making use of an updating process for the modes at each certain time step. Five transients have been studied: a homogeneous reactor, a non-homogeneous reactor, the 3D Langenbuch reactor and two transients related with in-phase and out-of-phase oscillations of Leibstadt NPP. The obtained results have been compared with the ones provided by a method based on a one-step backward discretization formula.     

Wavelet time–frequency analysis of accelerating and decelerating flows in a tube bank

In the present work, the steady approximation for accelerating and decelerating flows through tube banks is discussed. With this purpose, the experimental study of velocity and pressure fluctuations of transient turbulent cross-flow in a tube bank with square arrangement and a pitch-to-diameter ratio of 1.26 is performed. The Reynolds number at steady-state flow, computed with the tube diameter and the flow velocity in the narrow gap between the tubes, is 8 × 10⁴. Air is the working fluid. The accelerating and decelerating transients are obtained by means of start and stop of the centrifugal blower. Wavelet and wavelet packet multiresolution analysis were applied to decompose the signal in frequency intervals, using Daubechies 20 wavelet and scale functions, thus allowing the analysis of phenomena in a time–frequency domain. The continuous wavelet transform was also applied, using the Morlet function. The signals in the steady state, which presented a bistable behavior, were separated in two modes and analyzed with usual statistic tools. The results were compared with the steady-state assumption, demonstrating the ability of wavelets for analyzing time varying signals.     

广义分维在地震信号初至检测中的应用

基于地震信号的能量特征及广义分维的思想,给出一种新的地震信号初至估计算法。根据Mandelbrot-Richardson曲线截距的变化．可以准确检测到地震信号的初至。对于微弱地震信号初至的检测,首先按信号幅频特征的变化对原始记录进行预处理,在不改变地震信号初至的前提下,提高了记录的信噪比。对MR曲线的截距变化曲线进行类似于坐标旋转的校正．使对应信号初至的拐点成为曲线的极小值．有助于信号初至的自动检测。     

Particle identification using CsI(Tl) crystal with three different methods

Three pulse-shape-discrimination (PSD) methods are applied to study the particle identification (PID) by using CsI(Tl) crystal, especially for identifying light charged particles. The zero-cross time method, fast and total component method and signal rise time method are used. The experiment, data analysis and results are compared. Good PID for p, α and γ can be achieved with a CsI(Tl)-photomultiplier assembly.     

剂量仪中数字滤波器设计

单探测器宽量程剂量仪测量范围能超过8个数量级,远大于常规脉冲计数法的剂量仪。在单探测器宽量程剂量仪中,平均等待时间的计算误差直接关系到最终辐射强度或剂量率的计算精度。平均时间求取的实质是采用低通滤波器处理等待时间。信号处理领域中成熟的数字滤波器设计的基础是信号频谱分析,没有考虑核探测中的随机因素,由其设计的滤波器不能同时提高响应速度与测量精度这两个指标。针对单探测器宽量程剂量仪测量等待时间与数字滤波器设计方法的特点,本文提出了基于多目标粒子群优化的滤波器设计方法。理论分析与实验结果均表明：与传统方法所设计的滤波器相比,本文方法所设计的滤波器在相同测量精度条件下具有最快的响应速度;在相同响应速度条件下,具有最高的测量精度。本方法适用于设计宽量程剂量仪或其他类型辐射测量装置的数字滤波器。     

Analysis of a BWR Stability Behavior using Generalized Discrete Shannon Functions. Application to Ringhals and Forsmark Benchmarks Data

In this paper we have introduced a new methodology to on-line signal conditioning and monitoring to determine the stability parameters of the BWR NPP, that is, the determination of the effective Decay Ratio DR and the frequency of the main oscillation causing instability events. This method is based on the generalized discrete Shannon function convolution, which removes the noise and filters the signal in a specified frequency band. We have focused our attention in noise signals, first on analytic ones to check how the algorithm works, and then we have tested it with some real neutron signals. The algorithm works very well with dirty real signals providing good results, even in the case of short time series. Main attemption has been focused on decomposing signals to detect when a global and/or a regional oscillations are taking place in a BWR. This methodology can be implemented in on-line monitors to determine the stability parameters of the BWR reactors, that is, the determination of the effective decay ratio (DR) and the frequency of the main oscillation causing instability events.