摘要:

A brief review of the development of accelerators is given from Cockcroft‐Walton through the SSC. The usefulness of colliding beam devices is highlighted. (AIP) © 1995American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.47314

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Highlights of nonlinear beam dynamics experiments at the Indiana University Cyclotron Facility (IUFC) cooler storage rings and their implications on the design and operation of storage rings are presented. Our experimental results during the period of 1992–1993 can be classified in the following categories: (1) determination of nonlinear betatron Hamiltonian near 1‐D resonances, linear coupling resonance, and 2‐D difference and sum resonances; (2) determination of synchrotron Hamiltonian in the presence of the rf phase and the rf voltage modulations; (3) synchro‐betatron coupling induced by dipole field modulation; (4) attractors of a weak dissipative Hamiltonian system; and (5) effects of tune modulation on particles trapped in resonance islands. Based on our experimental results, we have analyzed data of synchro‐betatron coupling resonances at the Large Electron‐Positron Collider at CERN. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47311

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Modern hadron colliders are made with high‐field superconducting dipoles and quadrupoles that in general exhibit unintentional imperfections of the guiding field‐shape, due to construction tolerances, persistent currents, and saturation. Although the departure from linearity is typically small (a few units in 10−4at 1 cm from the axis), this phenomenon has a profound influence in the single‐particle beam dynamics. The non‐linear fields are at the origin of two effects: the betatron tunes change with the amplitude and the momentum of the circulating particles, and, for certain combinations of the horizontal, vertical, and synchrotron tunes, non‐linear resonances are excited. As a consequence, the stability of the particle motion can be considerably reduced, to the point that the dynamic aperture can become smaller than the physical aperture of the magnets. Analytical, numerical, and experimental approaches have been used to evaluate and possibly compensate mechanisms that lead to particle losses. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47306

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The dynamic aperture caused by persistent‐current nonlinear field errors is an important concern in the design of superconducting hadron storage rings. The HERA proton ring is the second superconducting accelerator in operation. In this lecture note, its measured dynamic aperture is compared with that inferred from comprehensive tracking studies. To understand the difference between prediction and measurement, a semi‐analytical method is developed for evaluating transverse diffusion rates due to various processes, such as modulational diffusion or sweeping diffusion. This analysis makes use of parameters for high‐order resonances in the transverse phase space, which are obtained by normal‐form algorithms using differential‐algebra software. The semi‐analytical results are consistent with the measurements, and suggest that the actual dynamic aperture is caused by an interplay of tune modulation and nonlinear magnetic fields. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47320

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Power supply ripple of the main dipoles and quadrupoles may further limit the dynamic aperture of large proton colliders such as the Large Hadron Collider (LHC) in the presence of the non‐linear field errors of the superconducting magnets. The Super Proton Synchrotron (SPS), the future injector of the LHC, is used to evaluate the effects of power supply ripple. These investigations will allow to specify the quality of the LHC main power supplies. In this report we demonstrate how the ripple spectrum measured at the power supplies of the different SPS magnet chains can be translated into an expected spectrum of tune ripple seen by the beam. To this end the transmission line characteristics of various single elements and magnet chains have been measured and compared to theoretical models. The damping effect of eddy currents induced in the vacuum chamber by the rippled main fields has been measured and compared to a preliminary model. The resulting tune spectrum is then compared with the actual tune ripple that has been measured with the Schottky system. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47312

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Hefei National Synchrotron Radiation Laboratory is the first dedicated synchrotron light source in China. The project started in 1984 and was completed in 1990. This paper describes the present status of the storage ring, results of machine study, and experimental research. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47313

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The main mechanisms for the excitation of synchro‐betatron resonances—i.e., dispersion in sextupoles and cavities, transverse fields in cavities, and beam‐beam interaction with a crossing angle—are reviewed. Experimental results and computer simulations are discussed. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47315

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The effects of the beam‐beam interaction on particle dynamics in a synchrotron collider are investigated. The main highlight of this work is the investigation of collective effects of the beam‐beam interaction in a self‐consistent approach that naturally incorporates the correct single particle dynamics. The most important target of this simulation is to understand and predict the long‐time (108–109rotations) behavior of the beam luminosity and lifetime.For this task a series of computer codes in one spatial dimension have been developed in increasing order of sophistication. They are: the single particle dynamics tracking code, the strong‐strong particle‐in‐cell (PIC) code, and the particle code based on the &dgr;falgorithm. The latter two include the single particle dynamics of the first. The third approach is used to understand beam lifetime by improving the numerical noise problem in the second.Scans in tune &ngr;0and tune shift &Dgr;&ngr;0show regions of stability and instability that correspond to the regions predicted by a linear theory. Strong resonance beam blowup is observed just above &ngr;0=1/2 and &ngr;0=1/4, where the rate of beam blowup drops with the order of the resonance.In both the strong‐strong code and &dgr;fcode using the reference parameters of the Superconducting Super Collider (SSC), oscillations in the tune shift &Dgr;&ngr; are observed. The odd moments of the beam increase in oscillation amplitude with rotation number, while the amplitudes of the even moments either decrease or remain constant. The ‘‘flip‐flop’’ effect is observed in the strong‐strong code simulations and is found to be sensitive to the initial conditions.In studying slow particle diffusion in the phase space of the beams away from resonances, the tracking code shows no diffusion of particles from the beam‐beam interaction after 105rotations. The strong‐strong code is found too noisy to study particle diffusion from the beam‐beam interaction. The much quieter &dgr;fcode shows all particles diffusive after 105rotations, in contrast to single particle tracking results. The diffusion coefficients are several orders of magnitude higher than the tracking code, and they increase exponentially with the action. However, this amount of diffusion (D∼10−10−10−11in the normalized unit) is still permissible for the SSC design parameters. This diffusion is caused by the collision induced variation of the second moment of the beam ⟨x2⟩. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47316

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The growth rate of the multibunch resistive instability at the SSC is calculated. The conditions for stabilization with tune spread are given. (AIP) © 1995American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.47317

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

After a short introduction of the wake potentials and coupling impedances, a few new results in impedance calculations are discussed. The first example is a new analytical method for calculating impedances of axisymmetric structures in the low frequency range, below the cutoff frequency of the vacuum chamber. The second example demonstrates that even very small discontinuities on a smooth waveguide can result in appearance of trapped modes, with frequencies slightly below the waveguide cutoff frequency. The high‐frequency (above the cutoff) behavior of the coupling impedance of many small discontinuities is discussed in the third example. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47318

出版商:AIP    

年代:1995

数据来源: AIP