342 research outputs found
Beam Coupling Impedances of Obstacles Protruding into Beam Pipe
The beam coupling impedances of small obstacles protruding inside the vacuum
chamber of an accelerator are calculated analytically at frequencies for which
the wavelength is large compared to a typical size of the obstacle. Simple
formulas for a few important particular cases, including both essentially
three-dimensional objects like a post or a mask and axisymmetric irises, are
presented. The analytical results are compared and agree with three-dimensional
computer simulations. These results allow simple practical estimates of the
broad-band impedance contributions from such discontinuities.Comment: 4 pages, LaTeX (REVTeX), 2 figures (eps); corrected and revised,
comparison with simulations added; presented at PAC97 (Vancouver, May 97
Stability and Halo Formation in Axisymmetric Intense Beams
Beam stability and halo formation in high-intensity axisymmetric 2D beams in
a uniform focusing channel are analyzed using particle-in-cell simulations. The
tune depression - mismatch space is explored for the uniform (KV) distribution
of the particle transverse-phase-space density, as well as for more realistic
ones (in particular, the water-bag distribution), to determine the stability
limits and halo parameters. The numerical results show an agreement with
predictions of the analytical model for halo formation (R.L. Gluckstern, Phys.
Rev. Letters, 73 (1994) 1247).Comment: 4 pages, LaTeX (REVTeX), 5 figures (eps); presented at PAC97
(Vancouver, May 97
A General Approach for Calculating Coupling Impedances of Small Discontinuities
A general theory of the beam interaction with small discontinuities of the
vacuum chamber is developed taking into account the reaction of radiated waves
back on the discontinuity. The reactive impedance calculated earlier is
reproduced as the first order, and the resistive one as the second order of a
perturbation theory based on this general approach. The theory also gives, in a
very natural way, the results for the trapped modes due to small
discontinuities obtained earlier by a different method.Comment: LaTeX, 3 pages (IEEE format), uses pac95.sty (20K
Recommended from our members
Parents as lay counselors : the development of a systematic parent program for drug counseling.
Transverse impedance of a resistive cylinder of finite length
In this report we calculate the transverse impedance of a charged particle beam, displaced from the axis of a circular cylindrical beam pipe which has finite resistivity only over a finite length. For this purpose we replace it with a cavity filled with the resistive material and connected to the region surrounding the beam by a gap of the same length. Matching of the electro-magnetic fields on both sides of the gap leads to an infinite set of linear equations for the field expansion coefficients with terms given by infinite sums over integrals which are evaluated by summing over their residues. By truncating these sums one can determine the transverse impedance and evaluate it numerically. Keeping only the lowest terms gives simple approximate expressions which are often sufficient to estimate the values and parameter dependence of the impedance
Halo Formation in Spheroidal Bunches with Self-Consistent Stationary Distributions
A new class of self-consistent 6-D phase space stationary distributions is
constructed both analytically and numerically. The beam is then mismatched
longitudinally and/or transversely, and we explore the beam stability and halo
formation for the case of 3-D axisymmetric beam bunches using particle-in-cell
simulations. We concentrate on beams with bunch length-to-width ratios varying
from 1 to 5, which covers the typical range of the APT linac parameters. We
find that the longitudinal halo forms first for comparable longitudinal and
transverse mismatches. An interesting coupling phenomenon - a longitudinal or
transverse halo is observed even for very small mismatches if the mismatch in
the other plane is large - is discovered.Comment: 3 pages, 3 figures; presented at European Particle Accelerator
Conference, Stockholm, Sweden (June 22-26, 1998
- …