Transition crossing in the Fermilab Main Ring, past and present

Abstract

A recent installation of passive mode dampers in the Booster has eliminated most of the longitudinal emittance blowup of intense bunches due to coupled-bunch instabilities. As a result, high intensity effects (negative-mass instability) dominate the present transition crossing in the Main Ring for the high-intensity cycles. A negative-mass stability limit is derived for transition crossing in the Main Ring and recent observations of high frequency signals around transition is presented. Finally, some predictions about the effect of the negative mass instability on the transition in the Main Ring with the future upgrades are attempted. >