Self-Bunching of a Circulating Beam in the U-70 Proton Synchrotron

The results of an investigation of self-bunching of the U-70 proton synchrotron beam are presented. The self-bunching arises on the top magnetic-field plateau and is caused by the interaction of the beam with the accelerating resonators from which the rf voltage was removed. A specific feature of self-bunching is its anomalously low threshold. It is shown that this is due to the filamentary beam structure, which appears during drfiting of the bunches, and the threshold is determined not by the total but rather the local momentum spread in each filament, continuously decreasing during drifting of the bunches. A novel method used in U-70 to suppress self-bunching is described.     

Longitudinal instability of a continuous beam in a proton synchrotron

The results of a calculation of the threshold for longitudinal coherent instability of a continuous beam circulating in a proton synchrotron and constant energy are presented. A beam in an intermediate state — not bunched into bunches but not uniform over the azimuth — is said to be continuous. Such a beam moves outside (possibly, near) empty rf separatrices of the longitudinal sinusoidal electric field and has a ribbon portrait in the longitudinal phase plane. The computational method is used for the U-70 synchrotron at the Institute of High Energy Physics, where in the course of stochastic slow extraction of a circulating beam is continuous in the sense indicated. It bends around empty separatrices of the 200-MHz accelerating field and for several seconds interacts with the electromagnetic fields of the working oscillations of the disconnected resonators of the main accelerating system with frequency 5.5–6 MHz, which can result in a loss of longitudinal stability. __________ Translated from Atomnaya énergiya, Vol. 104, No. 1, pp. 26–33, January, 2008.     

Upgrade of the Slow-Extraction System in the U-70 Proton Accelerator

The purpose of this work was to increase the efficiency of slow extraction of accelerated protons from the U-70 accelerator in order to provide the extracted beam for a physical setup requiring high intensity. On account of the limited power of the first extraction setup – an electrostatic deflector, the angle spread of the beam near the deflector barrier had to be decreased in order to decrease the losses and increase the efficiency. For this, the structure function was increased by inserting two additional quadrupole lenses into the magnetic structure of the accelerator. As a result of the inadequate strength of the system which corrects the frequencies of the betatron oscillations at the maximum accelerator energy 70 GeV, the beam was extracted at energy 64 GeV, where the frequency of the vertical betatron oscillations could be set above the line of the resonance 4Q _z = 39. As a result, the losses at the first two extraction setups increased by a factor of 3 and the efficiency of the slow-ejection system increased from 85% to 95%.     

Nonlinear analysis of nuclear coupled density wave instability in time domain for a boiling water reactor core undergoing core-wide and regional modes of oscillations

The objective of the paper is to develop a nuclear coupled thermal-hydraulic model in order to simulate core-wide (in-phase) and regional (out-of-phase) stability analysis in time domain within the limitation of desktop research facility for a boiling water reactor subjected to operational transients. The integrated numerical tool, which is a combination of thermal-hydraulic, neutronic and fuel heat conduction models, is used to analyze a complete boiling water reactor core taking into account the strong nonlinear coupling between the core neutron dynamics and primary circuit thermal-hydraulics via the void-temperature reactivity feedback effects. The integrated model is validated against standard benchmark and published results. Finally, the model is used for various parametric studies and a number of numerical simulations are carried out to investigate core-wide and regional instabilities of the boiling water reactor core with and without the neutronic feedback effects. Results show that the inclusion of neutronic feedback effects has an adverse effect on boiling water reactor core by augmenting the instability at lower power for same inlet subcooling during core-wide mode of oscillations, whereas the instability is being suppressed during regional mode of oscillations in presence of the neutronic feedback. Dominance of core-wide instability over regional mode of oscillations is established for the present case of simulations which indicates that the preclusion of the former will automatically prevent the latter at the existing working condition.     

Experimental study of natural circulation instability with void reactivity feedback during startup transients for a BWR-type SMR

The natural circulation boiling type SMR can experience flow instability during the startup transients due to the void reactivity feedback. A BWR-type natural circulation test loop has been built to perform the nuclear coupled startup transient tests for Purdue Novel Modular Reactor (NMR). This test loop is installed with different instruments to measure various thermal hydraulic parameters. The testing process can be monitored and controlled through PC with the assistance of LabVIEW procedure. The effects of power ramp rate on the flow instability during the nuclear coupled tests were investigated by controlling the power supply based on the point kinetics model with coolant void reactivity feedback. Two power ramp rates were investigated and the results were compared with those of the thermal hydraulic startup transients without void reactivity feedback. The time trace of power supply, system pressure, natural circulation rate, and void fraction profile are used to determine the flow stability during the transients. The results show that nuclear coupled startup transients also experience flashing instability and density wave oscillations. The power curves calculated from point kinetics model for startup transients show some fluctuations due to void reactivity feedback. However, the void reactivity feedback does not have significant effects on the flow instability during the startup procedure for the NMR.     

在NSRL上利用RFKO实现部分填充

RFKO系统在合肥光源电子储存环上的正常运行使合肥光源同步辐射光脉冲的时间结构变为可调，也克服了多束团不稳定现象，实现了高流强（350mA)的运行，为同步辐射用户提供了不同周期的同步光脉冲输出。     

Reactivity feedback calculation of a conceptual TRISO fueled compact PWR core

Reactivity feedback coefficients have been calculated for a compact sized PWR core that utilizes carbon coated micro fuel particles instead of standard cylindrical fuel pellets with an inventive composition. A small amount of Pu-240 with 5 w/o has also been added in tristructural-isotropic (TRISO) fuel in place of U-238 for the reduction of excess reactivity. The values of fuel, moderator and void reactivity coefficients have been calculated at the middle of fuel cycle. All the reactivity coefficients were found negative which meet the design safety criteria. It was also observed that all reactivity feedback coefficients are interlinked and their effects are pronounced when coupled together.     

Simulation of an hypothetical out-of-phase instability case in boiling water reactor by RELAP5/PARCS coupled codes

A very complex type of power instability occurring in boiling water reactor (BWR) consists of out-of-phase regional oscillations, in which normally subcritical neutronic modes are excited by thermal-hydraulic feedback mechanisms. The out-of-phase mode of oscillation is a very challenging type of instability and its study is relevant because of the safety implications related to the capability to promptly detect any such inadvertent occurrence by in-core neutron detectors, thus triggering the necessary countermeasures in terms of selected rod insertion or even reactor shutdown. In this work, simulations of out-of-phase instabilities in a BWR obtained by assuming an hypothetical continuous control rod bank withdrawal are being presented. The RELAP5/Mod3.3 thermal-hydraulic system code coupled with the PARCS/2.4 3D neutron kinetic code has been used to simulate the instability phenomenon. Data from a real BWR nuclear power plant (NPP) have been used as reference conditions and reactor parameters. Simulated neutronic power signals from local power range monitors (LPRM) have been used to detect and study the local power oscillations. The decay ratio (DR) and the natural frequency (NF) of the power oscillations (typical parameters used to evaluate the instabilities) have been used in the analysis. The results are discussed also making use of two-dimensional plots depicting relative core power distribution during the transient, in order to clearly illustrate the out-of-phase behavior.     

Phase instability of an intense electron beam in a storage ring

Radial-phase self oscillations in storage rings are considered for large beam currents. The stability conditions are obtained for the case of an arbitrary frequency characteristic of the accelerating system. The interaction of the beam with the accelerating system and other elements of the vacuum chamber at harmonics of the bunch-rotation frequency is also considered. Some results of experimental investigation into the self-excitation of phase oscillations in the storage rings of the Institute of Nuclear Physics in the Siberian Branch of the Academy of Sciences, USSR, are presented.Translated from Atomnaya Énergiya, Vol. 20, No. 3, pp. 210–213, March, 1966     

Incoherent instability of betatron oscillations in accelerators and storage rings

The problem of the transverse instability of a beam of charged particles circulating in a focusing system of the cyclical-accelerator or storage-ring type is considered. A dispersion equation for coherent vertical oscillations of the center of gravity of the beam is obtained and examined. It is shown that finite conductivity of the vacuum-chamber walls may lead to a dangerous instability. Conditions for the suppression of this are given and the maximum allowable number of particles circulating in the chamber is estimated.Translated from Atomnaya Énergiya, Vol. 19, No. 2, pp. 126–131, August, 1965     

摇摆运动条件下自然循环复合型脉动的实验研究

对摇摆运动条件下的自然循环两相流动不稳定性进行实验研究。实验结果表明：摇摆运动造成的两相流动不稳定性（波谷型两相流动不稳定性）和密度波型脉动相互叠加形成复合型脉动,加剧了系统的两相流动不稳定性。复合型脉动分为不规则的复合型脉动和规则的复合型脉动两部分,复合型脉动仅发生在高欠热度区域。规则的复合型脉动发生边界与相同热工水力参数下的密度波型脉动边界接近且受摇摆参数影响较小。     

上海同步辐射光源工作点稳定性研究

上海同步辐射光源（SSRF）是一台第3代高性能同步辐射装置,已稳定运行超过10年。储存环的线性光学模型稳定是光源稳定运行的基础。工作点反馈系统可实时地校正工作点,并间接地以降维的方式反馈难以在线测量到的线性光学函数。工作点反馈系统在SSRF的稳定运行验证了此方法的可行性,该反馈系统不仅使得工作点稳定度显著提升,也使得束流发射度、注入效率以及束流寿命等重要参数的稳定度得到大幅提升。衍射极限储存环光源是现阶段被广泛研究和建设的新一代同步辐射光源,工作点反馈系统也将发挥更重要的作用。本文分析电子储存环线性光学函数和工作点的稳定性,回顾SSRF工作点反馈系统的实际运行情况,介绍工作点反馈系统在SSRF衍射极限环lattice（SSRF-U）的模拟。工作点反馈在SSRF的实际运行情况和在SSRF-U的模拟结果显示,该系统可将工作点稳定在±0.001范围内,可满足储存环光源稳定运行和线性差耦合共振圆束斑模式对工作点稳定度的需求。     

Development of SIRIUS-N facility with simulated void-reactivity feedback to investigate regional and core-wide stability of natural circulation BWRs

The SIRIUS-N facility was designed and constructed for highly accurate simulation of core-wide and regional instabilities of a natural circulation BWR. A real-time simulation was performed in the digital controller for modal point kinetics of reactor neutronics and fuel-rod conduction on the basis of measured void fractions in reactor core sections of the thermal-hydraulic loop. Stability experiments were conducted for a wide range of thermal-hydraulic conditions, power distributions, and fuel rod time constants, including the nominal operating conditions of a typical natural circulation BWR. The results show that there is a sufficiently wide stability margin under nominal operating conditions, even when void-reactivity feedback is taken into account. The stability experiments were extended to include a hypothetical parameter range (double-void reactivity coefficient and inlet core subcooling increased by a factor of 3.6) in order to identify instability phenomena. The regional instability was clearly demonstrated with the SIRIUS-N facility, when the fuel rod time constant matches the oscillation period of density wave oscillations.     

Flashing-induced density wave oscillations in a natural circulation BWR—mechanism of instability and stability map

The SIRIUS-N facility was designed and constructed for highly accurate simulation of core-wide and regional instabilities of a natural circulation BWR. A real-time simulation was performed in the digital controller for modal point kinetics of reactor neutronics and fuel-rod conduction on the basis of measured void fractions in reactor core sections of the thermal-hydraulic loop. Stability experiments were conducted for a wide range of thermal-hydraulic conditions, power distributions, and fuel rod time constants, including the nominal operating conditions of a typical natural circulation BWR. The results show that there is a sufficiently wide stability margin under nominal operating conditions, even when void-reactivity feedback is taken into account. The stability experiments were extended to include a hypothetical parameter range (double-void reactivity coefficient and inlet core subcooling increased by a factor of 3.6) in order to identify instability phenomena. The regional instability was clearly demonstrated with the SIRIUS-N facility, when the fuel rod time constant matches the oscillation period of density wave oscillations.     

Vibration-RF Control of Superconducting-Helix Resonators for Heavy-Ion Acceleration

An electronic system for the control of the effects of RF frequency oscillations caused by mechanical vibrations in a superconducting helix are described. A combination of frequency modulation and amplitude modulation is used to lock the phase of a self-excited accelerating structure to that of a controlling master oscillator. The system has been used successfully during beam acceleration with a superconducting helix.     

Water level measurement uncertainty during BWR instability

This paper addresses the performance of the water-level measurement system in a boiling water reactor (BWR) during severe instability oscillations which, under some circumstances, can occur during an anticipated transient without SCRAM (ATWS). Test data from a prototypical mock-up of the water-level measurement system was used to refine and calibrate a water-level measurement system model. The model was then used to predict level measurement system response, using as boundary conditions vessel pressures calculated by RETRAN for an ATWS/instability event.The results of the study indicate that rapid pressure changes in the reactor pressure vessel which cause oscillations in downcomer water level, coupled with differences in instrument line lengths, can produce errors in the sensed water level. Using nominal parameters for the measurement system components, a severe instability transient which produced a 0.2 m peak-to-minimum water-level oscillation in the vessel downcomer was predicted to produce pressure difference equivalent to a 0.7 m level oscillation at the input to the differential pressure transmitter, 0.5 m oscillation at the output of the transmitter, and an oscillation of 0.3 m on the water-level indicator in the control room. The level measurement system error, caused by downcomer water-level oscillations and instrument line length differential, is mitigated by damping both in the differential pressure transmitter used to infer level and in the control room display instrument.     

Use of Short Silicon Crystals for Beam Extraction and Collimation in the U-70 Protron Synchrotron

The results of investigations of the extraction and collimation of the proton beam in the U-70 synchrotron at the Institute of High-Energy Physics, using short curved silicon single crystals 2–4 mm long, are presented.     

An equivalent linearization technique for two-phase flow instability analysis

An equivalent linearization technique has been developed to analyze two-phase flow instability oscillation with finite amplitude in the frequency-domain. A one dimensional slip flow model has been used to formulate equivalent linear equations, and implemented into a computer program.A simple boiling channel has been analyzed by the program. Results for very small amplitude oscillations agreed well with results by a detailed linear frequency-domain program.Analyses for larger amplitude oscillations gave more stable results. Limit cycle amplitudes have been calculated from the amplitudes at which channel characteristics change from unstable to stable as the amplitude is increased.