MEASURING CHROMATICITY ALONG THE RAMP USING THE PLL ∗

Beam stability up the ramp requires the appropriate sign and magnitude of the chromaticity. We developed a way to measure the chromaticity using the PLL (Phase Locked Loop) tune-meter. Since, the accuracy of the PLL tune-meter with properly adjusted loop gain is better than ≈ 0.0001 in tune units, the radial loop needs only be changed by a small amount of 0.2mm at a 1Hz rate. Thus, we can achieve fast chromaticity measurements in 1sec. Ex-cept during the very beginning of the ramp where there are snapback effects and the gamma changes very rapidly, we can have good chromaticity measurements along the ramp. This leads to the possibility of correcting the chromaticity during the ramp using a feedback system.