54864896
BEAM INSTABILITIY STUDIES OF BEPC AND BEPCII
BEPC has been well operated for more than 15 years, and it will be upgraded to a double ring electron positron collider in the existing tunnel, namely BEPCII. This paper describes the recent studies on beam instabilities for the improvement of BEPC performance as well as for BEPCII. The instabilities caused by impedance and twostream effects are investigated. The experimental and simulation results are reported.
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.
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.
126572691
Simulations of wake effects on a high-current electron beam at the KEKB injector linac
73585218
PRELIMINARY STUDY OF THE BEPCII IMPEDANCE
This paper summarizes the preliminary results on the impedance study of BEPCII, which is the upgrade of Beijing Electron Positron Collider (BEPC). Focus is on the longitudinal broadband impedance, which may lead to bunch lengthening and microwave instability. With the impedance of its main generating vacuum components being investigated, a primary impedance budget is obtained. The estimated impedance is below the impedance threshold of microwave instability.
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 )
119221336
Long-term X-Ray Monitoring of LS I +61°303: Analysis of Spectral Variability and Flares
We report on the full analysis of a Rossi X-ray Timing Explorer Proportional Counter Array monitoring of the γ-ray binary system LS I +61°303. The data set covers 42 contiguous cycles of the system orbital motion. Analyzing this X-ray monitoring data set, the largest to date for this source, we report on the variability of the orbital profile and the spectral distribution, and provide strong evidence for an anti-correlation between flux and spectral index (the higher the flux, the harder the spectral index). Furthermore, we present the analysis of two newly discovered kilosecond-timescale flares, which present significant variability also on shorter timescales and tend to occur at orbital phases between 0.6 and 0.9. However, a detailed timing analysis of the flares does not show any coherent or quasi-coherent (QPO) structure in their power spectra. We also investigated the possible appearance of the radio super-orbital modulation at X-ray energies, but we could not unambiguously detect such modulation in the system flux history nor in the evolution of its orbital modulation fraction.
16967478
High gradient experiments on NLCTA accelerator structures
This paper presents new results of high-gradient studies performed on a 1.8 m traveling-wave accelerator section with detuned high-order deflecting modes. This structure was designed initially for studies of detuned structures and will be installed in the Next Linear Collider Test Accelerator (NLCTA). The paper describes the test set-up in the Accelerator Structure Test Area (ASTA) including electron gun, prebuncher, pre-accelerator, spectrometer, Faraday cups, 200 MW SLED-II power compression system, Magic-T type phase shifters and attenuators. Rf processing, detailed dark current analysis, radiation problems, and beam acceleration measurements are discussed.
118506676
CO observation of SNR IC 443
We present our 12CO and 13CO mapping observations of SNR IC 443 interacting with molecular clouds. It is the first large-scale high-resolution 13CO mapping observation in the surrounding region. The morphologies of IC 443 in 12CO and 13CO are compared with the optical, infrared, Spitzer far-infrared, X-ray, and neutral atomic gas (HI). We also make comparison and analysis in the kinematics, using the date-cubes of 12CO, 13CO and HI, to help distinguish the complicated gas motions in the shocked regions. Based on the work of Wang & Scoville (1992), we present a new model to explain the coexistence of multiple shocks with different speeds in a pc-scale region at the central clump B. We test this new model by analyzing the HI and CO distribution in both velocity and space domain. We also establish the relationship between the dissociation rate of shocked molecular gas and the shock velocity in this region. Finally, we derive the optical depth of 12CO with the 13CO spectra in clump B, and discuss the validity of the assumption of optically thin emission for the shocked 12CO.
119035074
X-Ray Properties of the Point Source Population in the Spiral Galaxy NGC 5055 （M63） with Chandra
Using Chandra ACIS S3 data we studied the X-ray properties of low-and high-mass X-ray binary populations in the nearby spiral galaxy NGC 5055. A total of 43 X-ray point sources were detected within two effective radii, with 31 sources located on the disk and the rest 12 sources in the bulge. The resolved point sources dominate the X-ray emission of the galaxy, accounting for about 80% of the total counts in 0.3–10 keV. From spectral fittings we calculated the 0.3–10.0 keV luminosities of all the detected X-ray point sources and found that they span a wide range from a few times 1037 erg s−1 to over 1039 erg s−1. After compensating for incompleteness at the low luminosity end, we found that the corrected XLF of the bulge population is well fitted with a broken power-law with a break at 1.57+0.21−0.20×1038 erg s−1, while the profile of the disk population's XLF agrees with a single power-law distribution of slope 0.93+0.07−0.06. The disk population is significantly richer at 2×1038 erg s−1 than the bulge population, indicating that the disk may have undergone relatively recent, strong starbursts that significantly increased the HMXB population, although ongoing starbursts are also observed in the nuclear region. Similar XLF profiles of the bulge and disk populations were found in M81. However, in most other spiral galaxies different patterns of spatial variation of the XLF profiles from the bulge to the disk have been observed, indicating that the star formation and evolution history may be more complex than we have expected.
56077124
A closed orbit measurement with the NSRL BPM system
The beam position monitor system (BPM) of NSRL electron storage ring have a resolution of 10 microns with an accuracy of 50 microns, which is adequate fix beam position measurement and the closed orbit correction. The paper describes both of the BPM system and the closed orbit measurement.