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 )
56470793
DESIGN OF BEAM TRANSPORT LINE FROM RCS TO TARGET FOR CSNS
China Spallation Neutron Source (CSNS) uses the high energy proton beam to strike the Tungsten target to generate neutrons through spallation reaction. The proton beam is extracted from the Rapid Cycling Synchrotron (RCS), whose beam power reaches 100 kW. For the sake of target lifetime, beam distribution at the target surface is required as uniform as possible. Nonlinear beam density redistribution method with two octupole magnets has been studied. Also some simulation and theoretical calculation have been done. According to the simulation result, the beam density at the target is optimized and the beam loss is under control.
124075894
General conditions for self-cancellation of geometric aberrations in a lattice structure
In this paper we will discuss the general conditions for self-cancellation of geometric aberrations in an uncoupled or even coupled lattice structure. The self-cancellation conditions show that - I transformer even noninterleaved multipoles is not necessary. We will also give two examples for sextupole case to specify the application.
55843797
LATTICE DESIGN FOR THE BEPCII STORAGE RING
BEPCII, the upgrading project of the BEPC, has been being designed with a luminosity of 10 33 cm -2 s -1 at the J/ψ energy. It still keeps the potential to provide beams as a synchrotron radiation (SR) facility. The storage rings for collision contain a positron and an electron ring and the ring for dedicated SR uses the outer parts of the two rings. To fit all the conditions either on beam or on space limit, lattices are carefully designed for both high energy physics and SR experiments with sufficient dynamic apertures and high efficiencies for injection. The features of the lattices are also discussed in the paper. 1 DESIGN REQUIREMENTS BEPCII is an upgrade project of the Beijing ElectronPositron Collider (BEPC), in which a new inner ring will be installed inside the old one. It will provide colliding beams with the center-of-mass energy from 1.0GeV×2 to 2.0GeV×2 and also the dedicated synchrotron radiation beam with 2.5 GeV. For the colliding beams the luminosity is optimized at 1.89 GeV with 1×10 33 cm -2 s -1 . For the dedicated synchrotron radiation beam, the current is 250 mA with an emittance as low as possible. There have been several beam-lines in the BEPC for the synchrotron radiation experiments, so the current bending magnets and insertion devices in the southern region have to be fixed at their present positions. In order to increase the average luminosity, the “topoff” injection scheme up to 1.89 GeV is adopted. This requires that the injection and collision optics must be the same. The main parameters are shown in Tables 1 and 2.
60626146
ILC Reference Design Report: ILC Global Design Effort and World Wide Study
123594822
Transfer matrices of dipoles with bending radius variation
With the increasing demand of high brightness in light source, the uniform dipole can not meet the needs of low emittance, and thus the dipole with bending radius variation is introduced in this paper. The transfer matrix of a non-uniform dipole whose bending radius is linearly changed is chosen as an example and a very simple calculation formula of non-uniform dipole transfer matrices is given. The transfer matrices of some common profile non-uniform dipoles are also listed. The comparison of these transfer matrices and the matrices calculated with slices method verifies the numerical accuracy of this formula. This method can make the non-uniform beam dynamic problem simpler, very helpful for emittance research and lattice design with non-uniform dipoles.
110626236
Tests of MVD prototype pad detector with a β- source
Abstract The MVD group has been testing two versions of silicon pad detectors. One design uses a single metal layer for readout trace routing. The second type uses two layers of metal, allowing for greatly simplified signal routing. However, because the readout traces for the pads pass over the other pads in the same column (separated by an oxide layer), the double-metal design introduces crosstalk into the system. A simple test stand using a 90 Sr β − source with scintillator triggers was made to estimate the crosstalk. The crosstalk between pads in the same column of the pad detector was 1.6–3.1%. The values measured between pads in different columns were very close to zero. The measured crosstalk was below our maximum allowed value of 7.8%.
8517792
Measurement of the absolute branching ratio of the K+ ->pi+ pi0 (gamma) decay with the KLOE detector
We have measured the absolute branching ratio of the K+ → π+π0 (γ) decay, using ∼20 million tagged K+ mesons collected with the KLOE detector at DAΦNE, the Frascati φ–factory. Signal counts are obtained from the fit of the distribution of the momentum of the charged decay particle in the kaon rest frame. The result, inclusive of final-state radiation, is BR(K+ → π+π0 (γ))=0.2065± 0.0005stat ± 0.0008syst.
197468931
Study of jet shapes in inclusive jet production in pp collisions at sqrt[s]=7 TeV using the ATLAS detector
Jet shapes have been measured in inclusive jet production in proton-proton collisions at sqrt(s) = 7 TeV using 3 pb^{-1} of data recorded by the ATLAS experiment at the LHC. Jets are reconstructed using the anti-kt algorithm with transverse momentum 30 GeV < pT < 600 GeV and rapidity in the region |y| < 2.8. The data are corrected for detector effects and compared to several leading-order QCD matrix elements plus parton shower Monte Carlo predictions, including different sets of parameters tuned to model fragmentation processes and underlying event contributions in the final state. The measured jets become narrower with increasing jet transverse momentum and the jet shapes present a moderate jet rapidity dependence. Within QCD, the data test a variety of perturbative and non-perturbative effects. In particular, the data show sensitivity to the details of the parton shower, fragmentation, and underlying event models in the Monte Carlo generators. For an appropriate choice of the parameters used in these models, the data are well described.
120005485
STUDY OF ANGULAR DISTRIBUTION OF HELIUM PROJECTILE FRAGMENTS IN INTERACTIONS OF 200 A GeV 32S IONS WITH EMULSION NUCLEI
This paper presents data on the emission of helium fragments due to break up of 200 A GeV 32S ions in collision with emulsion nuclei. A total of 499 minimum bias events have been studied in an emulsion stack and 97 events in emulsion chambers. Emission angles of He fragments have been measured with high precision. This data has been compared with data of breakup of heavier as well as lighter projectiles and we observe that the value of the momentum spread, σ(p), increases with increasing projectile mass. The bulk part of the helium emission is consistent with a single source for helium fragments with an average excitation energy of (9.1±0.9) MeV. A tail of a few (<1%) He fragments with higher momenta is observed.
122689361
Search for New Phenomena with the Monojet and Missing Transverse Momentum Signature Using the ATLAS Detector in $\sqrt{s}=7$ TeV Proton-Proton Collisions
A search for new phenomena in events featuring a high energy jet and large missing transverse momentum in proton-proton collisions at root s = 7 TeV is presented using a dataset corresponding to an integrated luminosity of 33 pb(-1) recorded with the ATLAS detector at the Large Hadron Collider. The number of observed events is consistent with the Standard Model prediction. This result is interpreted in terms of limits on a model of Large Extra Dimensions. (C) 2011 CERN. Published by Elsevier B.V. All rights reserved.