Bunch lengthening in the Fermilab main ring during storage

Technical Report · Sat Jan 01 00:00:00 EST 1977

DOI:https://doi.org/10.2172/7211961· OSTI ID:7211961

Guignard, G.; Month, M.

There are two known current dependent effects which can increase the length of stored bunched beams: (1) a reduction of the potential well of the applied rf focusing system; and (2) induced unstable oscillations of the bunches, which can stabilize at a longer length by the process of Landau damping. In the first case, the current distribution in the bunches, interacting with induced electromagnetic fields in the walls, leaves a wake field which acts back on the bunches. A new equilibrium bunch shape results, different from that due to the applied rf, and this new equilibrium bunch shape will slowly establish itself as the particles within the bunch move on their new trajectories. The second form of bunch instability is the single bunch type. These are characterized by high frequency (i.e. within bunch) oscillations in the microwave region and fast growth rates. The coherent effects are very difficult to observe and such instabilities tend to simulate an incoherent growth in the bunch. An attempt is made to describe the observation of bunch lengthening in the main ring in terms of both potential well distortion and induced microwave fields. It is found that the increase in bunch size is in qualitative agreement with an induced microwave instability if the wall (i.e. chamber discontinuities) couples to beam with a broad resistive impedance in the microwave region of the order of Z/n approximately 75 OMEGA (n is the mode number of the oscillation of frequency f = nf/sub rev/).

• Research Organization: European Organization for Nuclear Research (CERN), Geneva (Switzerland); Brookhaven National Lab. (BNL), Upton, NY (United States)
• DOE Contract Number: EY-76-C-02-0016
• OSTI ID: 7211961
• Report Number(s): BNL-23045; TRN: 77-019359
• Country of Publication: United States
• Language: English

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FERMILAB ACCELERATOR
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OSCILLATIONS
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