Simulations of wake effects on a high-current electron beam at the KEKB injector linac

title: Longitudinal Impedance Measurements of the Components for the BEPCII
abstract: 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.

title: Recent studies on beam-photoelectron instability in BEPC
abstract: 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.

title: STUDIES ON THE BEAM CURRENT DEPENDENT PHENOMENA IN THE BEPC-II STORAGE RINGS
abstract: 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.  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 . 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.  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.  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 . 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 )

title: PRELIMINARY STUDY OF THE BEPCII IMPEDANCE
abstract: 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.

title: Electron cloud instability experiments on the BEPC
abstract: 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.

title: Minimization of Primary Electron Beam Radius at the Positron Production Target
abstract: 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.

title: Search for new physics in the multijet and missing transverse momentum final state in proton-proton collisions at $ \sqrt{s} $ = 8 TeV
abstract: A bstractA search for new physics is performed in multijet events with large missing transverse momentum produced in proton-proton collisions at $ \sqrt{s} $ = 8 TeV using a data sample corresponding to an integrated luminosity of 19.5 fb−1 collected with the CMS detector at the LHC. The data sample is divided into three jet multiplicity categories (3-5, 6-7, and ≥8 jets), and studied further in bins of two variables: the scalar sum of jet transverse momenta and the missing transverse momentum. The observed numbers of events in various categories are consistent with backgrounds expected from standard model processes. Exclusion limits are presented for several simplified supersymmetric models of squark or gluino pair production.

title: A closed orbit measurement with the NSRL BPM system
abstract: 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.

title: Electron reconstruction and identification efficiency measurements with the ATLAS detector using the 2011 LHC proton–proton collision data
abstract: Many of the interesting physics processes to be measured at the LHC have a signature involving one or more isolated electrons. The electron reconstruction and identification efficiencies of the ATLAS detector at the LHC have been evaluated using proton–proton collision data collected in 2011 at $$\sqrt{s}= 7$$s=7 TeV and corresponding to an integrated luminosity of 4.7 fb$$^{-1}$$-1. Tag-and-probe methods using events with leptonic decays of $$W$$W and $$Z$$Z bosons and $$J/\psi $$J/ψ mesons are employed to benchmark these performance parameters. The combination of all measurements results in identification efficiencies determined with an accuracy at the few per mil level for electron transverse energy greater than 30 GeV.

title: DESIGN OF THE JLC/NLC RDDS STRUCTURE USING PARALLEL EIGENSOLVER Omega3P
abstract: The complexity of the Round Damped Detuned Structure (RDDS) for the JLC/NLC main linac is driven by the considerations of rf efficiency and dipole wakefield suppression. As a time and cost saving measure for the JLC/NLC, the dimensions of the 3D RDDS cell are being determined through computer modeling to within fabrication precision so that no tuning may be needed once the structures are assembled. The tolerances on the frequency errors for the RDDS structure are about one MHz for the fundamental mode and a few MHz for the dipole modes. At the X-band frequency, these correspond to errors of a micron level on the major cell dimensions. Such a level of resolution requires highly accurate field solvers and vast amount of computer resources. A parallel finite-element eigensolver Omega3P was developed at SLAC that runs on massively parallel computers such as the Cray T3E at NERSC. The code was applied in the design of the RDDS cell dimensions that are accurate to within fabrication precision. We will present the numerical approach of using these codes to determine the RDDS dimensions and compare the numerical predictions with the cold test measurements on RDDS prototypes that are diamond-turned using these dimensions.