Measured optimum BNS damping configuration of the SLC linac

Transverse wakefield (or BNS) damping has been successfully used in the linac of the Stanford Linear Collider (SLC) to reduce emittance enlargement from beam trajectory jitter coupled with transverse wakefields. We are presently in the process of raising the bunch intensities from 3/spl times/10/sup 10/ particles per bunch to over 4/spl times/10/sup 10/. With these higher currents the RF phasing configuration which produces BNS damping must be improved. Too little "damping" allows excessive emittance growth from jitter but too much damping increases emittance growth from chromatic effects and produces an unacceptable loss of overall energy. Several experiments were performed to find the optimum settings for the present situation. An empirical optimum was found with a combination of 1) somewhat stronger BNS RF phase settings in the upstream section of the linac and 2) a stronger quadrupole lattice in the downstream section.<
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