20853925
Development of Longitudinal Coupling Impedance Measurement Platform for BEPCII
A coaxial line impedance measurement platform is developed for BEPCII under the collaboration between Tsinghua University and IHEP. A pair of gradual change impedance matching section is designed and fabricated by numerical control milling machine. The special designed RF connector is applied to strengthen the inner conductor. The algorithm of TRL calibration is applied in the system to avoid the usage of a reference pipe for each device under test. The measurement is accomplished by a VNA under the control of the software written in LabView.
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.
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.
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.
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.
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.
108862385
Accelerator Structure Bead Pull Measurement at SLAC
Microwave measurement and tuning of accelerator structures are important issues for the current and next generation of high energy physics machines. Application of these measurements both before and after high power processing can reveal information about the structure but may be misinterpreted if measurement conditions are not carefully controlled. For this reason extensive studies to characterize the microwave measurements have been made at SLAC. For the bead pull a reproducible measurement of less than 1 degree of phase accuracy in total phase drift is needed in order to resolve issues such as phase changes due to structure damage during high power testing. Factors contributing to measurement errors include temperature drift, mechanical vibration, and limitations of measurement equipment such as the network analyzer. Results of this continuing effort will be presented.
118438022
On the eccentricity distribution of short-period single-planet systems
We apply standard Markov chain Monte Carlo (MCMC) analysis techniques to 50 short-period, single-planet systems discovered with radial velocity technique. We develop a new method for accessing the significance of a non-zero orbital eccentricity, namelyanalysis, which combines the frequentist bootstrap approach with Bayesian analysis of each simulated data set. We find that the eccentricity estimations from theanalysis are generally consistent with the results from both the standard MCMC analysis and previous references. Themethod is particular useful for assessing the significance of small eccentricities. Our results suggest that the current sample size is insufficient to draw robust conclusions about the roles of tidal interaction and perturbations in shaping the eccentricity distribution of short-period single- planet systems. We use a Bayesian population analysis to show that a mixture of analytical distributions is a good approximation of the underlying eccentricity distribution. For short- period planets, we find the most probable values of parameters in the analytical functions given the observed eccentricities. These analytical functions can be used in theoretical investigations or as priors for the eccentricity distribution when analysing short-period planets. As the measurement precision improves and sample size increases, the method can be applied to more complex parametrizations for the underlying distribution of eccentricity for extrasolar planetary systems.
37988677
Development of Measurement and Transverse Feedback System at HLS
In order to cure and damp coupled bunch (CB) instabilities caused by the high order modes (HOMs) of the RF cavity and the resistive wall impedance of the Ring vacuum chamber. HOMs are ineluctable during the operation of the accelerator. An observer system characterized by bunch by bunch measurement of transverse β oscillation and longitudinal synchrotron phase oscillation has been constructed and commissioned at Hefei Light Source (HLS) [1, 2]. A transverse bunch-by-bunch feedback system is under construction. The design and development of the observe systems, as well as diagnostics results of machine instabilities are presented in this paper.
118033851
A Lattice Non-Perturbative Hamiltonian Construction of 1+1D Anomaly-Free Chiral Fermions and Bosons - on the equivalence of the anomaly matching conditions and the boundary fully gapping rules
A non-perturbative Hamiltonian construction of chiral fermions and bosons with anomaly-free symmetry $G$ in 1+1D spacetime is proposed. More precisely, we ask "whether there is a local short-range finite quantum Hamiltonian system realizing onsite symmetry $G$ defined on a 1D spatial lattice with a continuous time, such that its low energy physics produces a 1+1D anomaly-free chiral matter theory of symmetry $G$?" Our answer is "yes." In particular, we show that the 3$_L$-5$_R$-4$_L$-0$_R$ U(1) chiral fermion theory, with two left-moving fermions of charge-3 and charge-4, and two right-moving fermions of charge-5 and charge-0 at low energy, can be put on a 1D spatial lattice where the U(1) symmetry is realized as an onsite symmetry, if we include properly-designed interactions between fermions with intermediate strength. We show how to design such proper interactions by looking for interaction terms with extra symmetries. In general, we show that any 1+1D U(1)-anomaly-free chiral matter theory can be defined as a finite system on 1D lattice with onsite symmetry, by using a quantum Hamiltonian with a continuous time, if we include properly-designed interactions between matter fields. We comment on the new ingredients and the differences of ours comparing to Eichten-Preskill and Chen-Giedt-Poppitz models, and suggest modifying Chen-Giedt-Poppitz model to have successful mirror-decoupling. As an additional remark, we show a topological non-perturbative proof on the equivalence relation between 't Hooft anomaly matching conditions and the boundary fully gapping rules of U(1) symmetry.
54619300
Experimental progress in the measurement and control of single atom trajectory
In this review article, the progress and recent developments in the measuring and controlling of single atom trajectories are reviewed. With the development of laser cooling and trapping technology, it is possible to achieve the measurement and control of single atom trajectory experimentally. The experiment of tracking a single atom trajectory with high resolution and the endeavor of eliminating the degeneracy of the trajectories are then introduced.