摘要:

Space charge effects on beam dynamics in linear accelerators are discussed. Practical linac beam dynamics calculation methods which include space charge effects are discussed. Also, the status of beam performance experiments including space charge studies are summarized. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56764

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We discuss measurements on space charge dominated beams in circular accelerators, which could be of interest for high-current machines. In the transverse phase plane a crucial issue for high intensity is the direct observation of space charge, which was demonstrated recently at LEAR and the SIS by means of quadrupolar pick-ups. The issues of uniform and non-uniform space charge densities as well as mismatch oscillations are of interest in the context of halo formation and beam loss. For the longitudinal plane the self-bunching instability due to a resistive impedance has been measured in detail in the ESR and found to confirm very well the linearized theory; in the nonlinear phase of simulations modeling the experiment no overshoot was found, in contrast with theoretical predictions for beams without space charge. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56769

出版商:AIP    

年代:1998

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.56752

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We employ the Kapchinskij-Vladimirskij envelope Hamiltonian to describe the envelope evolution, and the particle Hamiltonian to describe particle motion in a space charge dominated beam. In a uniform focusing channel, particle motion can encounter parametric resonances arising from the envelope oscillations of a mismatched beam. Large amplitude envelope oscillation can cause global chaos near the vicinity of the beam core, and lead to enhanced halo formation. In a periodic focusing channel, enhancement of halo formation may also arise from structure resonances, i.e. envelope-lattice and particle-lattice resonances. The onset of global chaos exhibits a first order phase transition like behavior when the amplitude of envelope oscillations for a mismatched beam is larger than a critical value. The equations of motion for space charge dominated beams in synchrotron are derived. We find that the space charge force generates an identical defocusing function to the betatron motion and dispersion function. The self-consistent envelope equation obeys the Kapchinskij-Vladimirskij type equation similar to that of the linear transport system. We employ these results to analyze the stability of crystalline beams, and discuss the implication on the high intensity proton driver for the neutron spallation sources. Possible experiments are suggested. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56762

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The point is made that betatron resonances do not occur at the incoherent value of the tune, but rather at the frequencies of the appropriate collective modes. This has important implications not only for the design of high intensity, low energy proton synchrotrons, but also for the interpretation of machine studies at existing synchrotrons of this type. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56781

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have studied space charge effects in a synchrotron with multi-particle tracking in 2-D and 3-D configuration space (4-D and 6-D phase space, respectively). First, we will describe the modelling of space charge fields in the simulation and a procedure of tracking. Several ways of presenting tracking results will be also mentioned. Secondly, it is discussed as a demonstration of the simulation study that coherent modes of a beam play a major role in beam stability and intensity limit. The incoherent tune in a resonance condition should be replaced by the coherent tune. Finally, we consider the coherent motion of a beam core as a driving force of halo formation. The mechanism is familiar in linac, and we apply it in a synchrotron. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56782

出版商:AIP    

年代:1998

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.56783

出版商:AIP    

年代:1998

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.56784

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Average current from the PSR has been limited to ∼70 &mgr;A at 20 Hz by beam losses of 0.4 to 0.5 &mgr;A which arise from two principal causes, production ofH0excited states and stored-beam scattering in the stripper foil. To reduce beam losses, an upgrade from the two-stepH0injection to directH−injection is underway and will be completed in 1998. Peak intensity from the PSR is limited by a strong instability that available evidence indicates is the two-stream e-p instability. New evidence for the e-p hypothesis is presented. At operating intensities, the incoherent space charge tune shift depresses both horizontal and vertical tunes past the integer without additional beam loss although some intensity-dependent emittance growth is observed. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56765

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We will describe measurements of the beam in the Fermilab Booster during the first five milliseconds. Most of the particle losses in the Booster are over after the first few milliseconds. At high intensity of4×1012the transmission is 75&percent;. Such high beam loss can be a limiting factor for future high repetition rate operation of the Booster. The evidence, although indirect, suggests that the losses are the result of incoherent space-charge effects at low energy. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56766

出版商:AIP    

年代:1998

数据来源: AIP