The 1999／2000 Operation of Storage Ring for BEPC／BSRF

In this article,the operation status of BEPC/BSRF in 1999/2000 is mainly reviewed.BEPR is designed to serve as a research facility for both elementary particle physics and synchrotron radiation experiments.There were three major tasks for accelerator during this operation:Provide beams to BSRF for about 70 days which were distributed into three periods.operate for high energy physics experiments at 1.55 GeV to acquire more than 20 million J/ψ events.and finish the preliminarily machine studies which are relative to BEPC further upgrades and BEPC-II project studies.With the collaborative efforts of all the accelerator people,all the goals were achieved successfully at last.     

Construction of the Phasing System for BEPCⅡ Linac

In order to get high beam quality, a RF distribution system is required, with minimal phase drifts and errors in the BEPCⅡ linac. The additional installation of phase reference cables and monitoring equipments and stable RF distribution for BEPC linac are finished. The master oscillator is chosen to offer RF signal with low phase noise and a stable phase distribution system is built to deliver RF signal to each klystron. A phase and amplitude detector is constructed to measure the phase precisely and an IΦA unit is used for a phase shifter. Control software based on EPICS is used to connect all the units of the system, and a phasing method based on BPM is adopted to optimize the phase of each klystron. Now the phasing system is installed and tested in the klystron gallery of the BEPCⅡ linac.     

Design and simulation of the wire scanner for the injector linac of BEPCⅡ

BEPCⅡ, the upgrade project of Beijing Electron Positron Collider (BEPC), is an accelerator with large beam current and high luminosity, so an efficient and stable injector is required. Several beam diagnostic and monitoring instruments are used. A new diagnostic instrument — wire scanner, has been designed and will be used to measure the profile of the linac beam of BEPCⅡ. This paper describes the prototype of this system and the cause of heat generating of the wire. Some simulation results of the heat and force by using finite element method software—ANSYS^®,2) are presented and discussed.     

PAD Design for the Phasing System of BEPCⅡ Linac

Phase and amplitude measurement is one of the most important issues for the phasing system of BEPCⅡ linac. Two kinds of PAD, based on analog and digital I/Q demodulator respectively, have been constructed and tested in both laboratory and the klystron gallery of BEPCⅡ linac. A calibration algorithm based on LMS method is used to compensate the mismatches of the analog I/Q demodulator. Experiments show that both kinds of PAD run stably and can meet the requirements of the phasing system.     

Design of BEPCⅡ bunch current monitor system

BEPCⅡ is an electron-positron collider designed to run under multi-bunches and high beam current condition. The accelerator consists of an electron ring, a positron ring and a linear injector. In order to achieve the target luminosity and implement the equal bunch charge injection, the Bunch Current Monitor (BCM) system is built on BEPCⅡ. The BCM system consists of three parts: the front-end circuit, the bunch current acquisition system and the bucket selection system. The control software of BCM is based on VxWorks and EPICS. With the help of BCM system, the bunch current in each bucket can be monitored in the Central Control Room. The BEPCⅡ timing system can also use the bunch current database to decide which bucket needs to refill to implement ``top-off' njection.     

Construction of a New Set of fpc＇s for the Composite Pair

A new set of fpc is introduced to build the orthogonal set of basis for the states with many S and D pairs in the microscopic theory of low-lying collective motion.     

Measurement and correction of coupling in BEPCⅡ

The existing linear coupling theory and representation method are introduced briefly. The so-called local and global coupling is discussed in more detail. The vertical orbit distortion excited by a horizontal corrector is represented with the coupling parameters at the corrector and the observation point. The formula is used to measure the coupling in BEPCⅡ. In order to correct the coupling, vertical correctors are used to change the vertical orbit through sextupoles by a least square method. We also introduce and review other frequently used coupling measurement/tuning methods used in our machine.     

Design and optimization of a longitudinal feedback kicker cavity for the HLS-Ⅱ storage ring

In the Hefei Light Source (HLS) storage ring, multibunch operation is used to obtain a high luminosity. Multibunch instabilities can severely limit light source performance with a variety of negative impacts, including beam loss, low injection efficiency, and overall degradation of the beam quality. Instabilities of a multibunch beam can be mitigated using certain techniques including increasing natural damping (operating at a higher energy), lowering the beam current, and increasing Landau damping. However, these methods are not adequate to stabilize a multibunch electron beam at a low energy and with a high current. In order to combat beam instabilities in the HLS storage ring, active feedback systems including a longitudinal feedback system (LFB) and a transverse feedback system (TFB) will be developed as part of the HLS upgrade project, the HLS-Ⅱ storage ring project. As a key component of the longitudinal bunch-by-bunch feedback system, an LFB kicker cavity with a wide bandwidth and high shunt impedance is required. In this paper we report our work on the design of the LFB kicker cavity for the HLS-Ⅱ storage ring and present the new tuning and optimization techniques developed in designing this high performance LFB kicker.     

Construction of Generalized Synchronization for a Kind of Array Differential Equations and Applications

Chaos synchronization, as a special complex phenomenon, has been studied for about a decade. Only recently, have generalized chaotic synchronization phenomena been realized to be general in the real world and to have potential applications. We present two theorems for constructing a kind of array differential equations with generalized synchronization (GS) with respect to linear transformations. Two array differential equation systems with GS are introduced based on our theorems. Numerical simulations show that the two systems display periodic GS and chaotic GS, respectively.     

A New Type of Cascading Synchronization for Halo-Chaos and Its Potential for Communication Applications

Study of beam halo-chaos has become a key issue of concern for many future important applications. Control of halo-chaos has been researched intensively. This is the first time that the synchronization of beam halo-chaos has been realized in this field so far. Two nonlinear feedback control methods are proposed for the cascading synchronizing halo-chaos in coupled lattices of a periodic focusing channel. The simulation results show that the methods are effective. The realization of the synchronization of beam halo-chaos is significant not only for halo-chaos control itself but also for halo-chaos-based secure communication which may become an innovative technique.     

Design and construction of the MEBT1 for CADS injector scheme Ⅱ

A Medium Energy Beam Transport line 1(MEBT1) has been designed for Injector Scheme II of the China ADS project. To match the beam from RFQ to Superconducting(SC) Half Wave Resonator(HWR) sections with emittance preservation, the MEBT1 has been designed to be mechanically compact. Working at 162.5 MHz,the MEBT1 transports a 10 m A, 2.1 Me V proton beam using seven quadrupoles and two bunching cavities within2.7 meters. Three collimators are placed between every two adjacent quadrupoles to collimate the beam halo. Design and construction of the MEBT1 are presented in this paper.     

Progress of the Injector Linac Upgrade for the BEPCⅡ Project

BEPCⅡ—an upgrade project of Beijing Electron Positron Collider (BEPC) is a factory type of e+e- collider. It requires its injector linac to have a higher beam energy (1.89 GeV) for on-energy injection and a higher beam current (40 mA e+ beam) for a higher injection rate ( 50 mA/min). The low beam emittance (1.6π mm·mrad for e+ beam, and 0.2πmm·mrad for 300 mA e- beam) and the low beam energy spread (±0.5%) are also required to meet the storage ring acceptance. Thus the original BEPC injector linac must be upgraded to have a new electron gun with its complete tuning system, a new positron source with a flux concentrator, a new RF power system with its phasing loops and a new beam tuning system with orbit correction and optics tuning devices. These new components have been designed, fabricated, tested and will be installed in their final positions in this spring and summer, which are described in this paper.     

High power conditioning of the input coupler for BEPCⅡ superconductingcavity

High power conditioning of the input coupler for BEPCII superconducting cavity has been performed. After room temperature conditioning, the RF power of 150 kW with continuous wave at standing wave mode passed through the coupler without any problem. Meanwhile, a series of methods have also been studied to improve the performance of the coupler during the beam operation. Up to now, the input coupler can feed a RF power up to 100 kW stably with high current of 250 mA at 2.5 GeV.     

Design and Construction of a Three-Color Gold–Copper-Vapor Laser and the Output-Power Dependence on the Frequency and Buffer-gas Pressure

We design and construct a three-color gold–copper-vapor laser emitting green (510.6 nm), yellow (578.2 nm), and red (627.8 nm) light. The maximum measured total average output power is 12 W under sealed-off conditions. We divide the active medium into three zones (two at both ends for copper and the central zone for gold) in order to vaporize both gold and copper simultaneously. For this purpose, we use a single type of thermal insulator to change the temperature along the medium by varying its thickness, which is the main point in our design. In addition, we carry out some experiments to distinguish the dependence of the output power on the frequency and buffer-gas pressure; the measured ratio of these three wavelengths, green : yellow: red, is 22 : 10 : 7.     

Study on cooling process of cryogenic system for superconducting magnets of BEPCⅡ

In the upgrade project of the Beijing Electron Positron Collider (BEPCⅡ), three superconducting magnets are employed to realize the goal of two orders of magnitude higher luminosity. A cryogenic system with a total capacity of 0.5~kW at 4.5~K was built at the Institute of High Energy Physics (IHEP) to support the operations of these superconducting devices. For preparing the commissioning of the system, the refrigeration process was simulated and analyzed numerically. The numerical model was based on the latest engineering progress and focused on the normal operation mode. The pressure and temperature profiles of the cryogenic system are achieved with the simulation. The influence of the helium mass flow rates to cool superconducting magnets on the thermodynamic parameters of their normal operation is also studied and discussed in this paper.     

Logic of Quench Protection Assembly for BEPC-ⅡInteraction Region Superconducting Magnet

Two superconducting magnet complexes are used in BEPCⅡ interaction region. The corresponding quench protection system divides all related faults into two classes and takes different protection actions according to the urgency degree. Since BEPCⅡ has two operating modes and the superconducting magnets use different power supplies in different operating modes, the quench protection system must take the mode switching into consideration.     

Study of lower emittance dedicated synchrotron radiation mode for the BEPCⅡ

In this paper,a dedicated synchrotron radiation （SR） mode for the BEPCⅡ with an emittance of 85 nm has been designed,including the linear lattice,chromaticity correction and dynamic aperture optimization.The emittance of the new mode is about 60% of the previous mode used for routine operation of the BEPCⅡ .The effect of wigglers on the linear lattice was compensated and the total dynamic aperture including the wigglers’ nonlinear effect was estimated.The preliminary commissioning at the end of 2008 and the formal operation with the new mode confirmed its merits.