Beam-based optimization of SwissFEL low-level RF system

Swiss FEL is a free electron laser(FEL) under commissioning at the Paul Scherrer Institut(PSI) in Switzerland. Digital low-level RF(LLRF) systems are used in Swiss FEL to control more than 30 RF stations with either standing wave cavities(e.g. RF gun) or travelling wave structures working at different frequencies. After conditioned to desired power levels, the RF stations need to be setup for beam operation and the LLRF parameters need to be optimized for maximizing the beam stability. Several beam-based algorithms were developed to facilitate the setup, calibration and optimization of the Swiss FEL RF stations for beam operation. The algorithms were implemented as automation procedures in the framework of Experimental Physics and Industrial Control System(EPICS) and were used in commissioning and daily operation of Swiss FEL. In this paper, the algorithms and the implementation will be introduced together with the test results during the commissioning of SwissFEL.     

SXFEL装置上速调管输入输出特性曲线的线性化

在上海软X射线自由电子激光(Soft X-ray Free-electron Laser,SXFEL)中的微波低电平控制系统中,通过对各速调管的输出信号进行测量和控制,保证加速器的稳定运行并且达到技术指标。另一方面,SXFEL中的脉冲速调管的输入输出特性存在非线性的关系,这种电子管放大器不理想的非线性特性会导致微波低电平(Low Level Radio Frequency,LLRF)控制系统调节的效率降低。基于SXFEL装置,采用基于现场可编程门阵列(Field Programmable Gate Array,FPGA)的数字预失真方法,在LLRF控制系统中设计了一套实现高功率速调管放大器线性化的在线系统。S波段加速装置和其相应的东芝E3730A速调管及高压调制器和低电平系统实地测试结果表明,在LLRF控制系统中建立的在线系统能够有效补偿速调管带来的非线性问题,提高微波低电平控制系统的精度及准确性。     

用于回旋加速器低电平系统的通用软硬件系统设计与实现

针对回旋加速器射频系统幅度、相位、频率、自动启动逻辑、联锁保护、在线参数修改等控制需求，设计了一种用于回旋加速器低电平系统的软硬件系统。该系统的硬件基于ZYNQ系列FPGA和高速ADC及DAC。采用数字下变频技术实现了幅度、相位和调谐控制；采用数字电路实现了腔体打火的快速检测。幅度控制精度为0.015%，相位控制精度为0.04°。该系统充分发挥了数字低电平系统的全可编程优势，通过上位机修改参数即可适用于多种回旋加速器。     

Simulation studies on two-frequency RF gun

Photocathode RF gun is widely used for particle accelerators as an electron source.When driving an RF electron gun at the fundamental frequency and a higher harmonic frequency simultaneously with proper field ratio and relative phase,it generates electron beams of ultralow emittance and a linear longitudinal phase space distribution.Such a gun provides high quality electron beam with low energy spread,small traverse emittance and high brightness.In this paper,the RF design of a 1.5 cell cavity is presented.Simulation results of beam dynamics for the two-frequency gun and a standard single-frequency RF gun are also shown in this paper.In addition,bunch compression with a two-frequency gun is explored.     

230 MeV超导回旋加速器高频低电平系统设计与桌面实验研究

中国原子能科学研究院正在研发一台230 MeV医用超导回旋加速器,用于天津肿瘤医院的质子治疗项目。为满足加速器高频系统的腔体负载Dee电压稳定度、高频频率稳定度及加速电压幅度平衡度的要求,本文研制一套包含模拟数字混合型幅度环、数字型调谐环和数字型电压平衡环3个环路的低电平控制系统。该低电平系统通过串口与上位机进行通信,以实现本地调试;利用Profibus-DP通信协议,实现低电平系统和PLC组网的交互通信。在1个缩比例无氧铜实验腔体上完成了低电平系统低功率桌面实验与联合调试,验证了电压调平衡算法的有效性,并实现了低电平控制系统的一键启动,无需人工干预,满足了加速器高频系统对低电平控制系统的需求。     

Phase-stabilized RF transmission system based on LLRF controller and optical delay line

Radio frequency (RF) transmission systems with high-precision phase stability are required by the next generation of particle colliders and light sources.An RF transmission system was designed to meet this requirement.In this system,RF signal generated at the sending end is modulated onto a continuous wave (CW) optical carrier,transmitted through an optical fiber,and demodulated at the receiving end.The phase drift is detected by a digital phase monitor with femtosecond-level accuracy and compensated by a motorized optical fiber delay line (ODL).The measurement results show that the long-term phase drifts can be stabilized to within 100 fs (pk-pk),500 fs(pk-pk),and 1.8 ps (pk-pk) in a 400-meter-long optical fiber over 1 h,24 h,and 10 days,respectively.     

SHINE腔式BPM系统射频信号调理前端研制

基于低温超导直线加速器的上海硬X射线自由电子激光装置（SHINE）需1个分辨率可达200 nm的束流位置测量系统,以实现电子束与光子束在波荡器中的紧密相互作用和能量交换。现已研制的束流位置测量系统不能完全满足上述要求,为此,基于对关键技术指标的分配,设计研制了一个由C波段腔式探头、低噪声系数的单路下变频至低中频的射频信号调理前端以及专用数字信号束流位置处理器构成的CBPM系统样机。而作为连接腔式探头和数字信号采集电子学之间的桥梁,射频信号调理前端（radio frequency front end, RF前端）的结构和性能也直接决定了CBPM系统的性能。本文从SHINE对CBPM系统的整体需求为出发点,分析了系统对射频信号调理前端的指标分配,提出了一种放大器开关切换型RF前端的方案设计,并成功搭建了1套可模拟束流条件的离线全锁相采样测试平台。此外,在上海软X射线自由电子激光装置（SXFEL）中搭建了测试平台并完成了射频信号调理前端的带束性能评估,束流实验结果表明,在束团电荷量为100 pC、系统动态范围在±100 μm的条件下,采用腔式探头射频信号一分二的评估方法,位置分辨率可达71 nm,优于设计指标需求。     

15-MeV电子直线加速器的低电平系统

15-MeV电子加速器驱动的光中子源装置(TMSR Photo-Neutron Source Phase 1,TPNS1)是专为钍基熔盐堆(Thorium Molten Salt Reactor,TMSR)核数据测量设计和建造的。为保证直线加速器提供稳定的、高品质的束流,开发了基于可编程逻辑门阵列(Field Programmable Gate Array,FPGA)技术的低电平控制系统,利用上下变频、IQ(In-phase and Quadrature)调制解调技术实现了直线加速器幅度和相位的反馈控制。经测试,幅度和相位的控制精度达到±0.4%,可达±0.6°。长时间的运行表明,整个数字化环路的响应时间快,稳定性好,满足中子源装置的运行要求。     

基于FPGA的DDS信号获取与PI反馈算法设计

介绍了上海质子治疗装置高频低电平系统中扫频配置和PI反馈控制算法。通过编写Verilog HDL代码对AD9858芯片进行配置,实现了直接数字频率合成和频率扫描的功能,设计了PI算法以保证高频腔腔压幅度和相位的高精度和高稳定性。     

Laser-RF synchronization based on digital phase detector

Laser oscillator synchronization with RF reference signal is ultra-important for a modem light source based on the accelerator.For Tsinghua Thomson scattering X-ray source,we have synchronized the mode-locked laser oscillator to RF reference signal with 48.2 fs RMS relative jitter.Both fundamental and harmonic signals derived from photo diode detection are used for laser-RF synchronization in our scheme.The fundamental signal is for coarse laser-RF synchronization and multiple laser oscillator synchronization.The harmonic signal is for high precise phase locking.The digital phase detector is implemented in the synchronization scheme for less noise,replacing the mixing to DC phase detection scheme.The digital processing algorithm for synchronization is commonly used in low-level RF control field.In order to test the phase locking loop logic without damaging the real laser oscillator,a laser oscillator emulator was developed for phase locking.This paper will report the laser-RF synchronization scheme and its performance.The laser oscillator emulator system will also be introduced here.     

100 MeV Cyclotron LLRF Control Design and Details for RF Circuit

CEFR堆容器及堆内构件是一体化的池式结构。反应堆容器为双层结构，包括主容器和保护容器，堆容器直径约8m，高12．6m。一回路全部主要设备及部分二回路设备置于其中，结构紧凑而复杂。堆容器及部分堆内构件因体积庞大无法整体运至安装现场，因此，按照可运输的尺寸条件分成多个部分在工厂加工制造后运至现场。     

EPICS based low-level radio frequency control system in LIPAc

The IFMIF–EVEDA (International Fusion Materials Irradiation Facility – Engineering Validation and Engineering Design Activity) linear accelerator, known as Linear IFMIF Prototype Accelerator (LIPAc), will be a 9 MeV, 125 mA continuous wave (CW) deuteron accelerator prototype to validate the technical options of the accelerator design for IFMIF. The primary mission of such facility is to test and verify materials performance when subjected to extensive neutron irradiation of the type encountered in a fusion reactor to prepare for the design, construction, licensing and safe operation of a fusion demonstration reactor (DEMO). The radio frequency (RF) power system of IFMIF–EVEDA consists of 18 RF chains working at 175 MHz with three amplification stages each. The low-level radio frequency (LLRF) controls the amplitude and phase of the signal to be synchronized with the beam and it also controls the resonance frequency of the cavities. The system is based on a commercial compact peripheral component interconnect (cPCI) field programmable gate array (FPGA) board, provided by Lyrtech and controlled by a Windows host PC. For this purpose, it is mandatory to communicate the cPCI FPGA board from EPICS Channel Access [1]. A software architecture on EPICS framework in order to control and monitor the LLRF system is presented.     

用于DC-SC光阴极微波电子枪中的Cs2Te光阴极研制

文章介绍DC-SC光阴极微波电子枪中的关键部件——Cs2Te光阴极的研制。采用两种方法制得了高量子效率要求的Cs2Te光阴极，并实验比较了两种制备方法的效果。针对制备中的超高真空、精确控制Cs原子流量和阴极温度等关键问题，设计了用于DC-SC光阴极微波电子枪中的光阴极制备室。     

腔式束流位置探测器的设计与实验研究

束流位置探测器对自由电子激光装置的研制和运行具有重要的意义。其中,腔式束流位置探测器(腔式BPM)又以其高精度、高分辨率的特点而得到广泛的应用。本文对应用于上海深紫外自由电子激光装置上的腔式BPM进行了理论分析、模拟计算和BPM腔的测量等方面的研究。     

轫致辐射能谱测定SSC高频腔体电压

介绍了利用轫致辐射能谱测定回旋加速器高频腔体电压的原理，方法及测量结果。该测量方法的优点在于采用非接触方式量高频腔体电压，因而不改变高频腔体的谐振特性，并且不受高频频率的影响，测量的高频腔体电压准确可靠。     

用于回旋加速器射频低电平系统的通用DSP固件程序设计

针对回旋加速器射频系统幅度、相位、启动逻辑、联锁保护、在线参数修改等控制需求,编写了一种基于有限状态机的通用DSP固件程序。该固件程序将射频系统启动过程划分为5个状态:封锁RF信号、搜索腔体谐振点、提升射频功率、匹配相位、幅相闭环控制。该固件程序通过串口与本地上位机和远程控制机进行实时通信,支持在线修改射频系统启动参数;采用异步事件驱动方式,实现对打火和反射功率过大等异常情况快速响应。该固件程序成功应用于CYCIAE-100回旋加速器射频低电平系统中,在CYCIAE-100回旋加速器调束过程中,完成了射频系统的启动控制和设备保护,满足加速器控制系统的需求。     

基于千兆以太网的CSNS RCS射频分布式控制系统架构

中国散裂中子源(China Spallation Neutron Source,CSNS)快循环同步加速器的射频系统的远程控制系统采用基于千兆以太网的分布式体系结构,其软件架构使用国际加速器界广泛使用的开源软件工具EPICS(Experimental and Industrial Control System)进行开发。系统主要由CPCI低电平控制器、高功率四极管放大器和偏流源机器状态监控网络、联锁保护系统、中控中转服务器和人机交互界面组成。论文主要介绍了该系统的基本功能和拓扑结构,以及各个组成部分软硬件的设计和实现。     

Transfer function measurement for the SSRF SRF system

A digital transfer function measurement system has been embedded in the low-level radio frequency (LLRF) system of the storage ring of the Shanghai Synchrotron Radiation Facility. The measurement results indicate that the decreased control accuracy at high current is primarily owing to ripples from the high-voltage power supply, the transient beam loading effect, and the digital aliasing effect. The current LLRF algorithm is not able to suppress these disturbances.     

平行极板间等离子体RF共振特性研究

为探索用于ＡＶＬＩＳ的更为有效的离子引出方法,对等离子的ＲＦ共振离子出引方法进行了理论研究,用ＰＩＣ方法对其了模拟。结果表明：在弱磁场下可产生鞘层－等离子体振荡,其振荡频率与理论一致;外加与振荡频率王牟的交流电压后将发生共振,其振荡幅度大幅增加,电流加大,共振在等离子体中产生的最大电位幅可高于外加电压幅度几倍;与离子引出方法中传统的平行板电场相比,ＲＦ共振法使得出出的离子流加大,离子引出时间显著     

多线程通信方法在高频幅度控制中的应用

高频系统幅度控制环路开环时，束流将会在腔上引入与正常工作腔压可比的场，流强升高时束流要从腔上得到更多功率，此时腔自身消耗的功率保持不变，这就要求高频幅度控制发挥作用，满足束流和腔功率的要求。作为高频系统监控程序的一个组成部分，本文采用了多线程串口通信的方法实现了对SSRF高频系统激励电平的控制。