35215306
Longitudinal Impedance Measurements of the Components for the BEPCII
A longitudinal impedance measurement system was established for the BEPCII. The measurements, done in the frequency domain, are based on the coaxial wire method using HP/Agilent 8720ES network analyzer. The applications of the TRL calibration technique and absorbers were investigated to find a good approach for impedance measurements. The impedance, larger than 20 Ohm and below 6 GHz, can be measured using the TRL calibration technique in the experiment. And better measurement results were got using the reference pipes with the absorbers. So, this system satisfies the requirements of the BEPCII. This paper gives a review on this impedance measurements system for the BEPCII. The measurements results show that there are no serious impedance problems for BEPCII bellows and injection kickers, agreeing well with the numerical simulations. More improvements on this system are in progress.
53366099
Microwave instabilities in electron rings with negative momentum compaction factor
Bunch lengthening (or shortening) caused by the potential well distortion and the microwave instability in electron rings with negative momentum compaction factor is discussed in detail based on the resonator impedance model; further, a comparison with rings of positive momentum compaction factor is given. It was found that the bunch shape is less deformed and the current threshold of the microwave instability is higher in the rings with negative momentum compaction factor over a very wide range of the impedance parameters. The results also show that even within the range where the threshold for positive momentum compaction is higher than that for negative momentum compaction, the bunch lengthening is still less serious in most cases. Finally, an example of bunch lengthening in the case that /spl alpha/<0 with a real wake field of the SLC damping ring (old vacuum chamber) is given in contrast to the case in which /spl alpha/>0.
16640761
Recent studies on beam-photoelectron instability in BEPC
An experiment investigating the photoelectron instability has been performed in BEPC at IHEP, China. The betatron oscillation of each bunch was observed and recorded by a single pass beam position monitor system which has a capability to measure the transverse position of every bunch over 16000 turns. The effect of an octupole magnet on the instability was also studied. This paper describes results of those observations and analyses.
119741336
Electron cloud instability studies in the Beijing Electron Positron Collider
The electron cloud instability (ECI) in the Beijing Electron Positron Collider (BEPC) was studied systematically with experiments and simulations in recent years. Several electron cloud detectors have been installed into the BEPC storage ring to measure the electron yield. The effects of solenoid, the clearing electrode, the chromaticity, and the octupole on ECI have been investigated in BEPC experimentally. To evaluate the ECI in BEPCII, the upgrade project of BEPC, a computer code has been developed to simulate the electron density in the antechamber under different conditions, as well as the progress of the single bunch and coupled-bunch instabilities caused by the electron cloud. The experimental and simulation results, as well as the activities, are reported in this paper.
121523785
Electron cloud instability experiments on the BEPC
The electron cloud instability (ECI), which takes place in positively charged particle circular accelerators, is studied both experimentally and theoretically in the recent years. Many ECI-related experiments, including electron cloud (EC) measurement, beam parameter dependences, instability cure, etc., have been carried out on the Beijing Electron Positron Collider (BEPC) since 1996. A great number of fruitful results are obtained from these experiments, which also influence the simulation studies in the meantime. Ways to control the ECI are also studied in the experiments. Some achievements are beneficial for the BEPCII, the upgraded project of BEPC in the near future.
17279318
THE PROPOSED EXPERIMENTAL STUDY ON BEAM-PHOTOELECTRON INTERACTIONS IN BEPC
A vertical collective effect suspected as photoelectron instability (PEI) has been observed at Photon Factory (PF) of KEK in recent years. This phenomena may impose a limitation on the performance of the proposed B-Factories or T-c Factories. An experiment has been planned to test it using positron beam at Beijing Electron Positron Collider (BEPC) in 1996 under the cooperation between IHEP and KEK. Preliminary simulation results have shown that the PEI may occur in BEPC on the total beam current level of 40 mA over more than 20 bunches. The instrumentation for observation of PEI is jointly prepared by both sides of IHEP and KEK. The machine study has been scheduled and the experiment will progress under the conditions of the best machine performance.
20026118
The ninth data release of the sloan digital sky survey: first spectroscopic data from the sdss-iiI baryon oscillation spectroscopic survey
The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median z ~ 0.52), 102,100 new quasar spectra (median z ~ 2.32), and 90,897 new stellar spectra, along with the data presented in previous data releases. These spectra were obtained with the new BOSS spectrograph and were taken between 2009 December and 2011 July. In addition, the stellar parameters pipeline, which determines radial velocities, surface temperatures, surface gravities, and metallicities of stars, has been updated and refined with improvements in temperature estimates for stars with T eff -0.5. DR9 includes new stellar parameters for all stars presented in DR8, including stars from SDSS-I and II, as well as those observed as part of the SEGUE-2. The astrometry error introduced in the DR8 imaging catalogs has been corrected in the DR9 data products. The next data release for SDSS-III will be in Summer 2013, which will present the first data from the APOGEE along with another year of data from BOSS, followed by the final SDSS-III data release in 2014 December.
31953693
Development and Application of Bunch-By-Bunch Measurement System of HLS
This paper is intended to present the newly implemented wideband (100MHz) bunch oscillation measurement system, which is in nature a different method from the narrow-band (< 5MHz) facilities employed before. Basic formalism and implementation details of the system is introduced to illustrate the function of observing coupled bunch instabilities in time and frequency domain. The designed function includes detecting of transverse oscillation, synchrotron phase oscillation, as well as bunch filling pattern. Some diagnostics results of machine instabilities and application of this system are also discussed.
110247079
Charge division read-out in a 1.8-m-long wire chamber
This paper reports on the design and the test results of a charge division electronic read-out system for a charged particle proportional wire detector. Electronic calibration and probable error analysis of the system are also discussed. Position resolution for the system has been measured to be 4.8-mm FWHM on a wire of 1.8-m length (0.26%, relative). >
119112072
X-ray absorption variability in NGC 4507
We present a complete spectral analysis of an XMM-Newton and Chandra campaign of the obscured AGN in NGC 4507, consisting of six observations spanning a period of six months, ranging from June 2010 to December 2010. We detect strong absorption variability on time scales between 1.5 and 4 months, suggesting that the obscuring material consists of gas clouds at parsec-scale distance. The lack of significant variability on shorter time scales suggests that this event is not due to absorption by broad line region clouds, which was instead found in other studies of similar sources. This shows that a single, universal structure of the absorber (either BLR clouds, or the parsec-scale torus) is not enough to reproduce the observed complexity of the X-ray absorption features of this AGN.
964657
Beam loading compensation in the NLCTA
In the design of the Next Linear Collider (NLC), multibunch operation is employed to improve efficiency at the cost of substantial beam loading. The RF pulse that powers the accelerator structures will be shaped to compensate for the effect of the transient loading along the bunch train. This scheme has been implemented in the Next Linear Collider Test Accelerator (NLCTA), a facility built to test the key accelerator technology of the NLC. In this paper we describe the compensation method, the techniques used to measure the energy variation along the bunch train, and results from tests with NLC-like beam currents.