Subject: Horizontal dispersion anomaly correction From: Jim Crittenden Date: Tue, 01 Apr 2008 12:30:17 -0400 To: David Rubin , David Sagan , Mike Billing Dave, David, Mike When I presented my CESRV studies of the correction of the horizontal dispersion anomaly at the low-emittance tuning meeting of 21 Feb 08, showing that it could be reduced by a factor of about 3 using quadrupoles, I was asked a couple of questions requiring further investigation. One question was how much the phase was messed up by the correction and if putting weights on the phase would permit simultaneous phase/eta correction. I am working on that and will report back. The other question concerned the fact that there was some weight on QUAD_K1 in the optimization I showed at the time: http://www.lepp.cornell.edu/~critten/cesrta/talks/21feb08 This note answers that question. First, as a reminder, this is the anomaly we are talking about: http://www.lepp.cornell.edu/~critten/cesrta/notes/1apr08/MODE00119894.GIF It was measured with vertical correctors off on 8 Jan 08, except for one vertical steering in the IR. The correction using quads gives slightly different numbers today than it did on 21 Feb 08, but it still works just as well: http://www.lepp.cornell.edu/~critten/cesrta/notes/1apr08/MODE00119896.GIF CESRV interactive log: http://www.lepp.cornell.edu/~critten/cesrta/notes/1apr08/qcorr.txt This plot also shows the effect of the correction on the phase. The contribution to the merit function by QUAD_K1 is four times smaller than the one from ETA_X, but it has a big effect, as can be seen by turning of its weight: http://www.lepp.cornell.edu/~critten/cesrta/notes/1apr08/MODE00119902.GIF CESRV interactive log:http://www.lepp.cornell.edu/~critten/cesrta/notes/1apr08/qcorr_no_quad_k1_wgt.txt I do not understand why turning off the weight on QUAD_K1 results in a less effective dispersion correction. -- Jim ======================================================== James Crittenden Tel. (607) 255-9424 Wilson Synchrotron Laboratory Fax (607) 255-8062 Cornell University Ithaca, New York 14853-8001 ========================================================