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.
16215815
Design of 2x2 DLDS RF Components for JLC
We have studied a multi-mode Delay Line Distribution System (DLDS)[1][2] as the RF power distribution system from klystrons to RF structures for linear colliders. In particular, a 2×2 DLDS has been proposed and studied at KEK for Japan Linear Collider(JLC). It has been proved that the 2×2 DLDS is simple, bus has good transmission efficiency. We have designed RF components of a basic unit of a DLDS using the High Frequency Structure Simulator (HFSS) code[3]. They include the TE01 extractor, the TE11 to TE01 converter, and the TE11 to TE12 converter for TE12 mode. HFSS calculation of the system, which consists of TE01 extractor and TE11 to TE01 converter, shows that the transmission efficiency of each mode is better than 95%. A low power test model for the mode stability experiment in 55m long wave guide in DLDS is also being developed. Further study is underway.
124036431
Studies on electron cloud instability in the BEPC
The Electron Cloud Instability (ECI) may occur in a positively charged particle storage ring when the machine is operated with a multi-bunch beam. The related experiments have been carried out on the Beijing Electron Positron Collider (BEPC) since 1996. The phenomena of the ECI are mainly coupled bunch oscillation and transverse beam size blow up. The ECI studies at the BEPC are reviewed in this paper, both on experiments and on simulations. The potential methods to suppress the ECI in a positron storage ring have been summarized from the studies.
126065967
LUMINOSITY ENHANCEMENT AND PERFORMANCE IN BEPCII
120097073
Tune optimization of modern light sources
How to find suitable working points plays an important role in the optimization of the third-generation light sources. Different methods of frequency map analysis, super-periodic structural resonance analysis, and single resonance approach are applied to study the effects of various resonances on the beam dynamics for different working points, trying to find some general strategies of tune optimization. Several guidelines for tune choosing are given at the end of this paper.
202667892
STUDIES ON THE BEAM CURRENT DEPENDENT PHENOMENA IN THE BEPC-II STORAGE RINGS
The commissioning of the upgrade project of the Beijing Electron Positron Collider (BEPCII) started on Nov. 12, 2006. During the 1 and 2 stages of the commissioning of the BEPCII rings, we had got the luminosity one tenth of its design value, provided beams to synchrotron radiation users for ~ 4 months, and studied beam dynamics as well. In this paper, some preliminary results of the beam dynamics will be given. INTRODUCTION The upgrade project of the Beijing Electron Positron Collider (BEPC), BEPCII, is mainly composed of a linac, two transport lines and two storage rings in parallel for eand e+ beams, respectively. The two halves of the outer rings are connected as a synchrotron radiation (SR) ring, with 14 beam lines extracted from 5 wigglers and 9 bending magnets. The layout and other details of the three rings of BEPCII can be found in [1]. In this paper, we mainly discuss some beam current dependent phenomena in the collision rings, say, BER and BPR for eand e+ beams, respectively. Some main nominal parameters of the lattice are listed in Table 1. Table 1: Main parameters of the BEPCII collision rings Beam energy GeV 1.89 Circumference m 237.53 Beam current A 0.91 Bunch current / Bunch No. mA 9.8 / 93 Natural bunch length mm 13.6 RF frequency MHz 499.8 Harmonic number 396 Emittance (x/y) nm.rad 144/2.2 β function at IP (x/y) m 1.0/0.015 Crossing angle mrad ±11 Tune (x/y/s) 6.54/5.59/0.034 Momentum compaction 0.0237 Energy spread 5.16×10 Natural chromaticity (x/y) −10.8/−20.8 Luminosity cms 1×10 Both BER and BPR have same magnetic lattices with the super period number of 1. Figure 1 shows the Twiss functions in the interaction region, the RF region and the whole ring. In order to have a big emittance and a high beam current, a quasi-FODO structure with 10 dipoles and 2 missing dipoles in each arc is applied. In the second section, we will discuss the single bunch beam dynamics studies. Multi-bunch beam effects will be introduced in section 3. Some instabilities were observed and showed in section 4. At last, a summary will be given. Figure 1: Twiss functions in the IR (up-left), the RF region (up-right) and the whole ring (down) of BER/BPR SINGLE BUNCH BEAM DYNAMICS Optics correction After beams were injected smoothly into the rings, the β functions along the rings are measured before and after the optics corrections based on the measured response matrices [2]. The relative errors between the nominal and measured beta functions are less then 10% averagely. Other Twiss functions, such as dispersions and transverse tunes, were also measured and close to the design values. Under these circumstances, we could do some beam observations and measurements of other parameter. Beam energy spread Beam energy spread was measured with the method of longitudinal quantum lifetime. If the RF voltage is set to keep a relatively short beam lifetime, say 20 or 30 min, thus the longitudinal quantum lifetime can be considered as the dominant one. The beam energy spread at different bunch current could be estimated with the longitudinal momentum acceptance. Figure 2 shows the beam energy spreads at different bunch current in both BER and BPR. 5.1 5.14 5.18 5.22 5.26 0 3 6 9 12 Ib(mA) σ (Ε −4 )
121984352
The BES detector
Abstract The Beijing Spectrometer (BES) is a general purpose solenoidal detector at the Beijing Electron Positron Collider (BEPC). It is designed to study exclusive final states in e + e − annihilations at the center of mass energy from 3.0 to 5.6 GeV. This requires large solid angle coverage combined with good charged particle momentum resolution, good particle identification and high photon detection efficiency at low energies. In this paper we describe the construction and the performance of BES detector.
118658903
Young stellar clusters and star formation throughout the Galaxy
Most stars are born in rich young stellar clusters (YSCs) embedded in giant molecular clouds. The most massive stars live out their short lives there, profoundly influencing their natal environments by ionizing HII regions, inflating wind-blown bubbles, and soon exploding as supernovae. Thousands of lower-mass pre-main sequence stars accompany the massive stars, and the expanding HII regions paradoxically trigger new star formation as they destroy their natal clouds. While this schematic picture is established, our understanding of the complex astrophysical processes involved in clustered star formation have only just begun to be elucidated. The technologies are challenging, requiring both high spatial resolution and wide fields at wavelengths that penetrate obscuring molecular material and remove contaminating Galactic field stars. We outline several important projects for the coming decade: the IMFs and structures of YSCs; triggered star formation around YSC; the fate of OB winds; the stellar populations of Infrared Dark Clouds; the most massive star clusters in the Galaxy; tracing star formation throughout the Galactic Disk; the Galactic Center region and YSCs in the Magellanic Clouds. Programmatic recommendations include: developing a 30m-class adaptive optics infrared telescope; support for high-resolution and wide field X-ray telescopes; large-aperture sub-millimeter and far-infrared telescopes; multi-object infrared spectrographs; and both numerical and analytical theory.
123869228
Minimization of Primary Electron Beam Radius at the Positron Production Target
To have a high positron yield, it is extremely important to minimize the primary electron beam radius at the positron production target. Various effects on electron beam blow-up have been analyzed. By comparing the measured beam radius with simulation, result at current BEPC positron source,some concrete effects on beam blow-up have been described. A design study on minimizing the electron beam radius at BEPC-II positron source is given, and the ways to reach this goal have been summarized.
36795205
Observation of chi(c2) production in B meson decay.
We report the first observation of chi(c2) production in B meson decays. We find an inclusive B-->chi(c2)X branching fraction of (1.80(+0.23)(-0.28)+/-0.26) x 10(-3). The data set, collected with the Belle detector at the KEKB e(+)e(-) collider, consists of 31.9 x 10(6) BB events. We also present branching fractions and momentum spectra for both chi(c1) and chi(c2) production.
16521965
Systematic study of a large sample of NLS1 galaxies from SDSS: First results
This proceedings contribution summarizes first results obtained from a systematic study of 2011 NLS1 galaxies, as presented in Zhou et al. (2006, ApJS, 166, 128). The sample was compiled by examining the spectral parameters of galaxies and QSOs derived from SDSS DR3 data. We discuss some preliminary results on the statistical properties of the sample, such as the fraction of NLS1, the properties of broad and narrow emission lines, and emission in other wavebands. The black hole mass - velocity dispersion relation for NLS1s was re-examined using the velocity dispersion values estimated from the stellar absorption spectra of the host galaxies. Preliminary result from an X-ray study for a small subset using data obtained by XMM-Newton is briefly discussed.