摘要:

This paper describes the LEP commissioning experience gained up to now on imperfection diagnosis and possible corrections. It summarizes the work done and the results collected by a number of people on beam optics, collective effects and beam‐beam interactions. Concerning optics imperfections, the questions of the strong betatron coupling observed, its possible sources and ways to reduce the consequent undesirable effects are emphasized. Other observations on dispersion, optics irregularities, chromaticity and dynamic aperture are briefly mentioned. Under collective effects, predictions and measurements of transverse impedances and mode‐coupling instability threshold are presented, together with results on the longitudinal impedance and the unpredicted coupled‐bunch oscillations, damped by feedback. Recent measurements of synchro‐betatron resonance effects observed in varying bunch current and vertical tune are also reported. For beam‐beam interactions, the experimental limit on the beam‐beam strength parameter and its dependence on the tunes are shortly discussed. The concluding remarks underline that the understanding of these imperfections and their correction make it possible a continual improvement of the LEP performance.

ISSN:0094-243X    

DOI:10.1063/1.42294

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The Stanford linear Collider (SLC), accelerates sngle bunches of electrons and positrons to 47 GeV per beam and collides them with small beam sizes and at high currents. The beam emittances and intensities required for present operation have significantly extended traditional beam quality limits. The electron source produces over 1011e−in each of two bunches. The damping rings provide coupled invariant emittances of 1.8×10−5r‐m at 4.5×1010particles. The 50 GeV linac has successfully accelerated over 3×1010particles with design invariant emittances of 3×10−5r‐m. The collider arcs are now sufficiently decoupled and matched in betatron space, so that the final focus can be chromatically corrected, routinely producing spot sizes (&sgr;x, &sgr;y) of 2.5 &mgr;m at the interaction point. Spot sizes below 2 &mgr;m have been made during tests. Instrumentation and feedback systems are well advanced, providing continuous beam monitoring and considerable pulse‐by‐pulse control. The luminosity reliability is about 60%. Overviews of the recent accelerator physics achievements used to obtain these parameters and the present limiting phenomena are described for each accelerator subsystem.

ISSN:0094-243X    

DOI:10.1063/1.42326

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A summary of error considerations and related observations during HERA commissioning are presented. Focus is on those kinds of errors which are essential and specific for high energy colliders with particles stored in two different rings.

ISSN:0094-243X    

DOI:10.1063/1.42290

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

In a hadron collider, the stability of the particle motion is basically determined by the field‐shape imperfections of the superconducting dipoles, especially during the injection flat bottom, when the effect of the persistent currents is maximum and the transverse size of the beam is large. Some precautions can make the motion of the particles less sensitive to the nonlinear components of the guiding fields. Correcting multipoles can be foreseen in the regular cells, to reduce the non‐linear tune‐shift caused by the systematic components of the field errors. The variations of the orbit functions can be limited along the insertions. The closed orbit and the linear coupling can be corrected sufficiently well. Finally the ripple of the power supplies can be reduced as much as possible. Most of these concepts have been embedded in the design of the LHC and their beneficial effects on the dynamic aperture have been extensively evaluated by computer simulations. Cost optimization implies that the dynamic aperture of the LHC has to be mainly limited by the field‐shape imperfections in the dipoles rather than by the errors in the quadrupoles or by the mechanical limitation represented by the primary collimator, inserted to collect the halo particles before they hit the cold bore.

ISSN:0094-243X    

DOI:10.1063/1.42297

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A general formalism for compensating accelerator lattice functions is described. It is applied to the special cases of orbit smoothing, tune adjustment, beta function compensation, local and global decoupling, and vertical dispersion suppression. Some of these algorithms are implemented, and have performed robustly, in the thin element modeling code TEAPOT, analyzing the SSC circular accelerators, sometimes with a few beam‐position monotors assumed to be malfunctioning.

ISSN:0094-243X    

DOI:10.1063/1.42325

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

It is well known that the high‐order multipole field errors, which cannot be avoided in modern superconducting proton accelerators, lead to particle losses, which may occur after many turns around the machine. The easiest, but most expensive approach, for the detection of such particle losses is brute‐force tracking of many particles over long periods of time. Unfortunately, one is thereby always limited to some maximum number of turns owing to computational speed and the large number of cases to be studied. Predictive tools for an early detection of the phenomena leading to particle loss are therefore welcome. The detection of local chaos through the evaluation of Lyapunov exponents allows such a prediction in an easy and reliable manner. However, it is still an open question how the particles are actually driven to large amplitudes and why this may take long periods of time. Our aim here is to give a phenomenological picture for this slow instability, and to show how resonances, even of very high orders, enter into the loss mechanisms.

ISSN:0094-243X    

DOI:10.1063/1.42298

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This paper is a review of observations of emittance growth in Fermilab accelerators which are not due to coherent effects, but result from beam oscillations excited by external stimuli. Specific examples are presented in order to emphasize the magnitude of the effects which can cause measurable emittance growth.

ISSN:0094-243X    

DOI:10.1063/1.42310

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This paper summarizes the survey and alignment processes of accelerators and transport lines and discusses the propagation of errors associated with these processes. The major geodetic principles governing the survey and alighment measurement space are introduced and their relationship to a lattice coordinate system shown. The paper continues with a broad overview about the activities involved in the step by step sequence from initial absolute alignment to final smoothing. Emphasis is given to the relative alignment of components, in particular to the importance of incorporating methods to remove residual systematic effects in surveying and alignment operations. Various approaches to smoothing used at major laboratories are discussed.

ISSN:0094-243X    

DOI:10.1063/1.42311

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Linear coupling effects due to skew quadrupole fields have become more important for proton synchrotrons. Large tune shifts can be generated by linear coupling. A higher order tune shift, roughly quadratic in the skew quadrupole field, may be present, which may require a more complex correction system. There may be large shifts in the beta functions, and some reduction in the dynamic aperture. Analytical results have been found for the higher order tune shift and the beta function shifts. Numerical results for these effects are given for RHIC, and a correction system is proposed for these effects. A correction system with about 4 or 5 families of skew quadrupole correctors appears able to correct the above effects.

ISSN:0094-243X    

DOI:10.1063/1.42312

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

In this report we attempt the exact solution of the motion of a charged particle in a circular accelerator under the effects of skew quadrpole errors. We adopt the model of error distributions, lumped in locations with zero extension. This thin‐lens approximation provides an analytical insight to the problem to any order. The total solution is expressed in terms of driving terms which are actually correlation factors to several order. An application follows on the calculation and correction of tune‐splitting and on the estimate of the role the higher‐order terms play in the correction method.

ISSN:0094-243X    

DOI:10.1063/1.42313

出版商:AIP    

年代:1992

数据来源: AIP