Transverse mode coupling in a bunched beam

Conference · Mon Aug 01 04:00:00 EDT 1983 · IEEE Trans. Nucl. Sci.; (United States)

OSTI ID:5507816

Chin, Y; Satoh, K

Since the fast transverse instability was observed in PETRA and, more recently, in PEP, this instability has become a critical problem in the design of large storage rings. The reason is that this instability imposes the serious limitation on a stored current; as soon as the current exceeds the threshold, the bunch distribution begins to blow up vertically or horizontally more rapidly that the synchrotron oscillation, and beam particles are lost. Short range fields created by the beam in RF cavities are considered to play an important role. The fast instability has been explained in terms of mode coupling in the longitudinal phase space or head-tail turbulence by other authors. The purpose of this paper is to derive a formalism of the mode coupling theory for a Gaussian bunch beginning from Sacherer's integral equation. The problem is reduced to solving the determinant equation for eigenfrequencies of coherent oscillations. Eigenfunctions are expressed as superposition of the linear independent functions where higher radial modes and azimuthal modes are combined and rearranged into ''hybrid'' modes. The theory is applied to explaining the fast instability observed in PEP and to a preliminary estimate of the threshold current in the TRISTAN electron-positron storage ring. The transverse broad-band impedances of RF cavities in PEP and TRISTAN are calculated with the program code TBCI and characterized by a single low-Q resonator impedance. A satisfactory agreement with PEP experimental results is obtained.

• Research Organization: Nat.'l Lab for High Energy Physics, Oho-machi, Tsukuba-gun, Ibaraki-ken 305
• OSTI ID: 5507816
• Report Number(s): CONF-830311-
• Conference Information: Journal Name: IEEE Trans. Nucl. Sci.; (United States) Journal Volume: NS-30:4
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
430200* -- Particle Accelerators-- Beam Dynamics
Field Calculations
& Ion Optics
430400 -- Particle Accelerators-- Storage Rings
BEAM BUNCHING
BEAM DYNAMICS
INSTABILITY
OSCILLATIONS
PEP STORAGE RINGS
PETRA STORAGE RING
STORAGE RINGS
SYNCHROTRON OSCILLATIONS
TRISTAN STORAGE RINGS