Simulations of the longitudinal instability in the new SLC damping rings

Conference · Thu Jun 01 04:00:00 EDT 1995

OSTI ID:64174

Bane, K L.F.; Oide, K

In 1992 a longitudinal, single bunch instability was observed in the SLC damping rings. Beyond a threshold current of 3 x 10{sup 10} a {open_quotes}saw-tooth{close_quotes} variation in bunch length and energy spread was observed, a phenomenon that made it practically impossible to operate the SLC collider above threshold. For the 1994 run a new, low-impedance vacuum chamber was installed in both damping rings both to alleviate this problem and to shorten the bunch length. According to recent measurements the bunch length has indeed become shorter, but the {open_quotes}saw-tooth{close_quotes} instability is still seen, now beginning at currents of 1.5-2.0 x 10{sup 10}. Fortunately, it appears to be benign and does not seem to limit SLC performance. In an earlier paper the authors investigated the single bunch behavior of the SLC damping rings with the old vacuum chamber using time domain tracking and a Vlasov equation approach. When compared to measurements they found: good agreement in the average values of bunch length, energy spread, and synchronous phase shift as functions of current; a 30% discrepancy in threshold current; in agreement, a mode with frequency near 2.5 times the synchrotron frequency (the so-called {open_quotes}sextupole{close_quotes} mode) as signature of the instability and the slope of the mode frequency as function of current. In the present paper they repeat the exercise of the earlier paper but with a new wakefield. The impedance which used to be inductive has become resistive, leading to different phenomena. In a recent paper the instability in a purely resistive ring is analyzed using a Vlasov equation approach. It is demonstrated that such an instability is a weak instability, with a growth rate proportional to intensity squared, and one that can be described as the coupling of two quadrupole modes with different radial mode numbers. The authors compare their results with this paper.

• Research Organization: Stanford Linear Accelerator Center, Menlo Park, CA (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: AC03-76SF00515
• OSTI ID: 64174
• Report Number(s): SLAC-PUB--95-6878; CONF-950512--80; ON: DE95012508
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
BEAM BUNCHING
INSTABILITY
LENGTH
STANFORD LINEAR COLLIDER