Experimental investigation of coupling impedances of the VEPP-4M electron-positron collider

The interaction of a beam with vacuum chamber elements via induced electromagnetic field is analyzed in the frequency domain using frequency-dependent coupling impedances. The knowledge of the impedances makes it possible to estimate the stability conditions for propagation of the beam. The calculation of impedances of accelerators like the VEPP-4M electron-positron collider with a large number of inhomogeneities in the vacuum chamber is a complicated and time-consuming problem. However, the impedances can be studied in such cases experimentally by analyzing the propagation of the beam. The results of experiments on the longitudinal and transverse impedances of VEPP-4M are considered. We describe a method for measuring the local transverse impedance ensuring a higher sensitivity as compared to the methods used earlier.     

New optical diagnostics of the VEPP-4M collider

The experiments in measuring the dynamic aperture and beam energy spread of the VEPP-4M collider [1] are described. The optical diagnostics of the accelerator were applied for these purposes. The text was submitted by the authors in English.     

Experiments on the physics of charged particle beams at the VEPP-4M electron-positron collider

The VEPP-4M accelerator facility with a universal KEDR detector is designed to conduct experiments with colliding electron-positron beams. High-energy physics, nuclear physics, and studies using synchrotron radiation are the main directions of research with this facility. In addition, experiments on poorly explored issues in the physics of beams in the electron-positron storage ring and methodological studies to prepare an experiment aimed at testing corollaries of the CPT theorem for an electron and a positron are regularly conducted at the VEPP-4 facility. A number of works performed in recent years are described: studies to increase the accuracy of comparing the electron and positron spin precession frequencies by the resonant depolarization method; measurements of the count rate of Touschek electrons as a function of the beam energy in a wide range; comparison of the methods for measuring the beam energy spread; a study of the electron beam dynamics when a nonlinear betatron resonance is crossed.     

RF system for VEPP-5 damping ring

This paper presents the RF system of VEPP-5 damping ring created at BINP Novosibirsk. The RF system operates at 700 MHz and consists of a generator based on KU-393 klystron, a transmitting waveguide with wave-to-coax adapters, an accelerating cavity, and a control system. Cavity HOMs are damped with resistive loads to eliminate the beam instability. Parameter results of cold measurement tests and high-power level tests are presented.     

BEPCII横向束流反馈系统的梳状滤波器

 BEPCII是一个多束团、大流强的装置, 由于高频腔的高次模和电阻壁阻抗等因素，不可避免地会出现束流不稳定性。BEPCII中采用束流反馈系统来抑制束流不稳定性。横向束流反馈系统主要包括前端电子学、信号处理电子学、反馈器件和放大器等几个部分。梳状滤波器是信号处理电子学的重要部件，利用两根长短不同的电缆以及一个功分器和合成器构成了一种简单有效的梳状滤波器，其梳状深度达到-41 dB，使用这种梳状滤波器的横向反馈系统成功地抑制了束流中出现的不稳定性。     

基于射频功率调节的负离子源束流反馈控制研究北大核心CSCD

基于射频负离子源的中性束注入系统是高功率长脉冲(稳态)运行中性束注入系统的最佳选择。负离子源是中性束注入系统的核心部件,需要实现稳定的负离子束引出和加速。在负离子源的运行过程中引出负离子电流会发生变化,尤其在长脉冲、高能量运行条件下会更加明显,因此无法满足稳定运行的要求。为了实现引出束流的稳定引出,开展了束流反馈控制研究,研发了一套基于射频功率调节的束流反馈控制系统,并将束流反馈控制系统应用在射频负离子源测试平台,开展了束流反馈控制测试。测试结果表明束流反馈控制系统能够实现对束流的实时反馈调节以获得束流的稳定引出,验证了基于射频功率调节的束流反馈控制的可行性,为高功率射频负离子源的研制提供支持。     

The VEPP-2000 electron-positron collider: First experiments

In 2007, at the Institute of Nuclear Physics (Novosibirsk), the construction of the VEPP-2000 electron-positron collider was completed. The first electron beam was injected into the accelerator structure with turned-off solenoids of the final focus. This mode was used to tune all subsystems of the facility and to train the vacuum chamber using synchrotron radiation at electron currents of up to 150 mA. The VEPP-2000 structure with small beta functions and partially turned-on solenoids was used for the first testing of the “round beams” scheme at an energy of 508 MeV. Beam-beam effects were studied in strong-weak and strong-strong modes. Measurements of the beam sizes in both cases showed a dependence corresponding to model predictions for round colliding beams. Using a modernized SND (spherical neutral detector), the first energy calibration of the VEPP-2000 collider was performed by measuring the excitation curve of the phimeson resonance; the phi-meson mass is known with high accuracy from previous experiments at VEEP-2M. In October 2009, a KMD-3 (cryogenic magnetic detector) was installed at the VEPP-2000 facility, and the physics program with both the SND and LMD-3 particle detectors was started in the energy range of 1–1.9 GeV. This first experimental season was completed in summer 2010 with precision energy calibration by resonant depolarization.     

High vacuum ionization chamber with high spatial resolution for monitoring synchrotron radiation beams

The possibility of using an ionization chamber with a cutting collectorin vacuum (10⁻⁴–10⁻⁵ Pa) for online monitoring of the position of a synchrotron radiation (SR) beam is studied experimentally The possibility of measuring the vertical position of the SR beam with a precision of up to several micrometers is demonstrated in the high vacuum conditions of an open channel in the VEPP-4M storage ring (in the absence of a beryllium window). Two such ionization chambers operating synchronously and situated one after another can serve as a basis for the SR beam stabilization system in neighboring channels.     

Longitudinal beam emittance blow-up caused by injection errors in synchrotrons with a longitudinal feedback system

The problem of longitudinal beam emittance blow-up caused by injection errors in synchrotrons with a longitudinal feedback system is studied. The obtained results are used to estimate parameters of a longitudinal feedback system.     

上海光源数字化低电平控制系统的硬件设计与实现

 设计了上海光源高频低电平控制系统,它是以数字化技术为基础,采用上下变频和IQ调制解调技术,实现幅度、频率和相位的反馈控制。上海光源储存环的束流设计流强为300 mA,为了抑制由此带来的Robinson不稳定性和纵向零模束流振荡,加入了高频直接反馈和零模束流反馈环路。从上下变频技术、IQ调制解调技术、时钟分配及锁相技术等方面对上海光源数字化低电平系统的硬件设计及其实现进行了阐述,给出了该系统试验、高功率下运行的测试结果,实现了设计要求的幅度控制精度±1%、频率控制精度 ±10 Hz和相位控制精度± 1°的技术指标。     

Experimental research on the spatial positions of SI beams in beamlines Nos. 13 and 7 of the VEPP-4M ring

Dynamics of the positions of SI beams was experimentally investigated over time in beamlines No. 13 and No. 7 in the VEPP-4M storage ring. An ion chamber with cutting electrodes was used in our research. The operability of the scheme of beam line No.13 is demonstrated. The ion chamber is tested in a regime in which the energy of the electrons in the storage ring is 3.5 GeV.     

Experimental investigation of high-energy photon splitting in atomic fields

Data analysis of an experiment in which photon splitting in atomic fields was observed is presented. The experiment was performed at the tagged photon beam of the ROKK-1M facility at the VEPP-4M collider. In the energy region of 120-450 MeV, statistics of 1.6x10(9) photons incident on the BGO target was collected. About 400 candidate photon-splitting events were reconstructed. Within the attained experimental accuracy, the experimental results are consistent with the calculated exact atomic-field cross section. The predictions obtained in the Born approximation differ significantly from the experimental results.     

BEPCII横向束流反馈系统前端电子学

 选择了一台商业化的前端电子学RFTF（radio frequency front-end for transverse feedback system）用于BEPCII横向束流反馈系统, 这是跟进世界先进加速器技术的具体实施。在BEPC同步运行模式下对RFTF的性能进行了测试实验，结果表明使用RFTF可以得到理想的波形，能够满足BEPCII横向反馈系统的需要，但是，当储存环出现不稳性时，系统无法正常工作，这就要求BEPCII纵向不稳定很小或者用纵向反馈系统来抑制存在的纵向不稳定。     

逐圈测量系统在合肥光源数字反馈调试中的应用

 使用逐圈测量系统作为观测手段,通过对逐圈测量系统采集所得数据进行分析,判断了数字反馈系统调试过程中的反馈效果。在改变六极铁电流以逐步改变储存环的色品值的过程中,通过逐圈测量系统观察了束流不稳定性,计算得到振荡增长时间和阻尼时间分别为0.258 ms和1.172 ms。并测量和计算了工作点、相空间等束流特性参数,分析了束流靠近和穿越5/9共振线的完整过程。     

Energy scale calibration of the KEDR tagging system

The KEDR detector tagging system is a symmetric focusing magnetic spectrometer of small-angle electrons born in the interaction region of the VEPP-4M collider. Using this system, which is designed for studying the two-photon processes, the scattered electrons and positrons energy is measured with a resolution of ΔE/E₀= 0.03–0.6% where E₀ is the beam energy. Two different methods are employed for calibrating the tagging system energy scale: the first one involves the electron/positron tagging by the energy of the singlebremsstrahlung photon measured in the BGO calorimeter, and the second one is based on the determination of the recoil electrons spectrum edge in the Compton backscattering of monochromatic laser radiation. The technical implementation and the present status of the calibration system are discussed in this paper.     

Equipment for soft X-Ray lithography on the VEPP-4M

An X-ray scanner for X-ray mask lithography is described. It is mounted onto the synchrotron radiation (SR) beamline of the VEPP-4M storage ring. The main advantage of this scanner is the possibility of varying the SR spectral range within wide limits and its fine tuning for solving specific technical tasks by changing the working energy of the VEPP-4M and using corresponding filters, which is illustrated by tables and plots of the calculated spectra. Calculated estimates of the lithographic resolution of lithographic complex, exposure times for various types of X-ray masks, and thicknesses of their masking layers providing the required level of X-ray mask contrast are given.     

Comparative certification of secondary-electron multipliers within the ultrasoft X-ray range

The results of studying the band characteristics and the efficiency of recording the secondary-electron multipliers VEU-6 and VEU-GOI (manufactured by the Vavilov State Optical Institute (GOI), St. Petersburg) within the ultrasoft X-ray range are given. The measurements were carried out at the metrological station Kosmos with the use of synchrotron radiation from the storage ring VEPP-4M (Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences, Novosibirsk) in monochromatic radiation at a photon energy of 268 eV. A strong irregularity in the band characteristics of both VEU-6 and VEU-GOI has been found. Their quantum efficiencies are estimated. The measurements are a continuation of the works on calibration of the equipment of the Space Solar Patrol (developed by GOI) using synchrotron radiation from the VEPP-4M storage ring (project MNTTs no. 2500).     

模拟低频反馈系统的初步尝试

 为了提高注入束流的积累，抑制由于注入系统误差引起较大的β残余振荡是非常有必要的。较系统地介绍了利用合肥光源逐圈测量（turn by turn）系统［１］，研究束流不稳定性，并给出了抑制注入β振荡的反馈系统设计原理和线路及初步实验结果。作为原理论证和预研，使用了一个相对简单的模拟滤波移相器对Kicker过程激发的β振荡进行反馈，得到了明显的对damping时间和振荡幅度的抑制作用，为以后低频和高频逐束团（bunch by bunch） 反馈系统研制和抑制束流的横向和纵向不稳定性的研究打下了良好的基础。     

VEPP-2000 collider commissioning

Construction of the VEPP-2000 construction was completed at the end of 2006. The first beam was captured in a special regime without final focus solenoids. In this regime, all systems of power supplies and machine control were calibrated and tuned. In the same mode vacuum chamber treatment by synchrotron radiation was performed with an electron beam current of up to 150 mA. The first test of the round beam option was performed at an energy of 508 MeV with a solenoidal field of 10 T in two straight sections of interaction. The text was submitted by the author in English.