[en] This work is an attempt to extend Robinson's stability studies to include a higher rf harmonic. Using an equivalent circuit model, the stability of the ''0-mode'' coherent dipole oscillation of bunched beams is studied for synchrotrons or storage rings, with rf systems operated at the fundamental and a higher harmonic, i.e., a 2nd and 3rd harmonic. Analytical expressions of the stability criteria are derived from the linearized equations. Numerical examples of stability are given for fully nonlinear cases

[en] This work is an attempt to extend Robinson's stability studies to include a higher rf harmonic. Using an equivalent circuit model, the stability of the ''O-mode'' coherent dipole oscillation of bunched beams is studied for synchrotrons or storage rings, with rf systems operated at the fundamental and a higher harmonic, i.e., a 2nd or 3rd harmonic. Analytical expressions of the stability criteria are derived from the linearized circuit equations. Numerical solutions of the fully nonlinear equations are provided to compare with the analytical results. Simple feedback model for stabilization is discussed

[en] The electron-proton instability of a long, intense, and partially neutralized proton bunch is studied by numerically solving the equations of motion for the line centroid of the proton beam and the line centroid of the trapped electrons. The formalism takes into account the effects of variable line densities and alternating-gradient focusing. Good qualitative agreement between the computational results and experimental observations was obtained when applying the theory to the Los Alamos Proton Storage Ring (PSR). Both the case of a clean extraction gap and the case with a few percent of protons in the extraction gap were studied. It is found that with only a few percent neutralization, the PSR beam can become unstable in both cases. The same equations and method were used to study the stability of the proton beam in the accumulator ring of the proposed LANSCE II spallation-neutron source. The results indicate that the e-p instability can also occur in the LANSCE II accumulator ring for only a few percent neutralization

[en] We studied the possibility of the occurrence of transverse instability induced by trapped electrons in unbunched beams in the Proton Storage Ring and the proposed Advance Hadron Facility (AHF) at Los Alamos, as well as in the proposed Kaon Factory at TRIUMF. We found that the e-p instability may be possible for unbunched beams in the PSR but is unlikely to occur in the advanced hadron facilities. 8 refs., 4 figs

[en] In the high-intensity unbunched-beam experiments carried out in the Proton Storage Ring at Los Alamos National Laboratory, the threshold current of vertical transverse instability showed pronounced differences when the betatron tune varied across an integer. In this paper, we shall present our experimental observations and discuss the possible relations between the threshold current and the machine impedance. The possible effects related to the distorted closed orbit are also discussed. 5 refs., 3 figs., 1 tab

[en] We studied the electrostatic fields due to the longitudinal and transverse perturbations of a charged particle beam with a uniform distribution propagating inside an rf-shielding cage constructed from evenly-spaced conducting wires. Simple formulae are derived for estimating the space-charge impedances. Numerical examples are given for illustration

[en] 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 the e-p instability 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

[en] This paper reports on an approach to investigate the dynamics of halo particles in mismatched charged-particle beams propagating through periodic-focusing channels using the particle-core model. The proposed method employs canonical transformations to minimize, in new phase-space variables, the flutter due to the periodic focusing to allow making stroboscopic plots. Applying this method, we find that in periodic-focusing systems, certain particles initially not in the halo region can be brought into resonance with the core oscillation to become halo particles. (c) 2000 The American Physical Society

[en] The design and construction of second-generation free-electron laser (FEL) system at Los Alamos will be described. comprising state-of-the art components, this FEL system will be sufficiently compact, robust and user-friendly for application in industry, medicine, and research. 11 refs., 11 figs., 2 tabs

[en] We present, in this paper, a new method for calculating the wake potential of a bunched beam of arbitrary charge distribution, directly from the wake potential of a shorter bunch, by using orthogonal polynomial expansions. Combined with the table-look-up technique, this method leads to an effective computation scheme for repetitive evaluation of wake potentials of different charge distributions under the same boundary conditions. 15 refs