13,714 research outputs found
Polarizabilities of an Annular Cut in the Wall of an Arbitrary Thickness
The electric and magnetic polarizabilities of an aperture are its important
characteristics in the theory of aperture coupling and diffraction of EM waves.
The beam coupling impedances due to a small discontinuity on the chamber wall
of an accelerator can also be expressed in terms of the polarizabilities of the
discontinuity. The polarizabilities are geometrical factors which can be found
by solving a static (electric or magnetic) problem. However, they are known in
an explicit analytical form only for a few simple-shaped discontinuities, such
as an elliptic hole in a thin wall. In the present paper the polarizabilities
of a ring-shaped cut in the wall of an arbitrary thickness are studied using a
combination of analytical, variational and numerical methods. The results are
applied to estimate the coupling impedances of button-type beam position
monitors.Comment: Uuencoded gzipped PS-file, 7 pages, 5 figures (110K) Submitted : IEEE
Transactions on Microwave Theory and Technique
Cavity Loss Factors For Non-Ultrarelativistic Beams
Cavity loss factors can be easily computed for ultrarelativistic beams using
time-domain codes like MAFIA or ABCI. However, for non-ultrarelativistic beams
the problem is more complicated because of difficulties with its numerical
formulation in the time domain. We calculate the loss factors of a
non-ultrarelativistic bunch and compare results with the relativistic case.Comment: 3 pages, 3 figures; presented at European Particle Accelerator
Conference, Stockholm, Sweden (June 22-26, 1998
Wake Field Effect Analysis in APT Linac
The 1.7-GeV 100-mA CW proton linac is now under design for the Accelerator
Production of Tritium (APT) Project. The APT linac comprises both the normal
conducting (below 211 MeV) and superconducting (SC) sections. The high current
leads to stringent restrictions on allowable beam losses (<1 nA/m), that
requires analyzing carefully all possible loss sources. While wake-field
effects are usually considered negligible in proton linacs, we study these
effects for the APT to exclude potential problems at such a high current. Loss
factors and resonance frequency spectra of various discontinuities of the
vacuum chamber are investigated, both analytically and using 2-D and 3-D
simulation codes with a single bunch as well as with many bunches. Our main
conclusion is that the only noticeable effect is the HOM heating of the 5-cell
SC cavities. It, however, has an acceptable level and, in addition, will be
taken care of by HOM couplers.Comment: 3 pages, 6 figures; presented at European Particle Accelerator
Conference, Stockholm, Sweden (June 22-26, 1998
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