摘要:

Beam spectra observed during the development of a coupled bunch instability contain information about the coupled bunch mode n, which describes the phase shift between adjacent bunch oscillations. This number indicates the possible frequency of the guilty impedance with accuracy up to an integer multiple of the bunch spacing frequency. However when there are many possible candidates with imprecisely known frequencies this can be insufficient. In this paper we discuss what additional information about the frequency of the source of instability can be obtained from the analysis of the unstable beam spectra envelope. This is applied to the measurements in the CERN SPS. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301890

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

In this paper, results from impedance measurements on the RHIC injection kickers are reported. The kicker is configured as a “C” cross section magnet with interleaved ferrite and high-permittivity dielectric sections to achieve a travelling wave structure. The impedance was measured using the wire method in which a resistive match provides a smooth transition from the network analyzer to the reference line in the set-up. Accurate results are obtained by interpreting the forward scattering coefficient via the log-formula. The four kickers with their ceramic beam tubes contribute aZ/n=0.22&hthinsp;&OHgr;/ringin the interesting frequency range from 0.1 to 1 GHz, and less above. At frequencies above ∼ 100 MHz, the impedance is ferrite dominated and not affected by the kicker terminations. Below 100 MHz, the Blumlein pulser with the ∼75 m feeding cables is visible in the impedance but makes no significant contribution to the results. The measurements show that the kicker coupling impedance is tolerable without the need for impedance reducing measures. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301891

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We review the definition and concepts of the longitudinal space charge impedance, and the formulas for its calculations. The conditions, limitations, and corrections in applying these formulas are discussed. Especially, we emphasize the various geometry factors associated with this parameter. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301892

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The use of Second Harmonic (SH) rf is being investigated to increase the RCS current limit. Hofmann-Pedersen distributions are employed to provide analytical guidance. The SH phase &thgr;, is optimized using a numerical analysis to maximize transmission and minimize instabilities. The effect of the RCS stainless steel liner on the impedance of the machine is also discussed. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301893

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Collective instabilities in intense charged particle beams described self-consistently by the Vlasov-Maxwell equations are studied using a 3D multispecies nonlinear perturbative particle simulation method. The electron-proton (e-p) two-stream instability is observed in the simulations carried out with the newly-developed Beam Equilibrium Stability and Transport (BEST) code. This code provides an effective numerical tool to investigate collective instabilities, periodically-focused beam propagation in alternating-gradient focusing fields, halo formation, and other important nonlinear processes in intense beam propagation. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301894

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

A computer program has been implemented for simulating the electron-proton instability of a partially neutralized long proton bunch. The simulation is based on a theoretical model that considers the motions of the proton-beam centroid and macro-particles representing electrons as well as the contribution of secondary emission of electrons due to impingement of particles on the beam pipe. Preliminary results from simulating thee-pinstability in the PSR are consistent with earlier studies using the centroid model and qualitatively agree well with experimental observations. It is found that enhancement of the instability due to the electron multiplication occurs only when oscillation of the proton beam has grown to large amplitude. This simulation program can be also used to find the beam-intensity threshold for multipactoring. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301895

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The Proton Storage Ring (PSR) in Los Alamos has a fast intensity-limiting instability, which may result from an electron cloud interaction with the circulating proton beam leading to a transverse mode coupling instability. The most probable mechanism of the electron creation is multipacting. Though the effect depends on many parameters, a model is presented which predicts a large electron creation in the vacuum chamber. A comparison of this effect between the PSR in Los Alamos and the Spallation Neutron Source (SNS) in Oak Ridge is given. In addition, several possibilities to reduce multipactor are discussed. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301896

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The fast loss electron proton instability is studied both experimentally and theoretically. It is shown that electron multi-pactoring is required for fast beam loss. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303089

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Taking advantage of the vastly different time scales of the problem, a simple analytical model of HOM induced relaxation oscillations has been developed. First a continuous approximation of the impulsive discrete forces is made. Then only the components of the force with the synchrotron frequency are retained to describe the slowly varying amplitude and frequency of the relaxation oscillation. A two particle version of this model reproduces the main characteristics of the system. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301897

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The concept of the surface impedance is applicable to the case, when obstacles on the surface of a vacuum chamber are small compared to characteristic dimensions of the problem. We apply this concept to the calculation of a synchronous mode that can propagate in a tube with slightly corrugated walls. We also show that such a mode can propagate in a pipe with a rough surface, or a perforated pipe with a large number of holes. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301898

出版商:AIP    

年代:1999

数据来源: AIP