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Dear Okugi-san, Thank you for your comments about IP beam size tuning. When comparing your results obtained when assuming the set of error used in mine, I am surprised that you do not need the octupole magnet. Actually even if I perfectly removed all 2nd order aberrations I do still have a significant contribution to Y-beam size growth due to U3222. In order to understand this issue, I wonder if in your lattice design process you use the FD octupole magnets. In my designed lattice for Ecm=500GeV I make use of the FD octupole magnets to reach the TDR beam sizes, maybe these octupoles introduce the mentioned aberration. Also regarding the errors, do you include errors from the movers (2um) in your simulation? Thanks much, Edu On 04/06/2015 02:05 AM, Okugi, Toshiyuki wrote: > Dear all, > > Since I could not connect the BDS meeting (3/30) well by my network problem, > I will make a comment for the IP beam size optimization with octupoles. > > When we use the higher order multipole fields to focus the beam core, > the tail particles will be spray and it makes the collimation depth small in generally. > Therefore, it is better to focus the beam with lower order correction, if possible, > and we can focus the beam only with sextupoles for ILC FFS (see attached file). > > Furthermore, when we assumed the errors in the beamline, > the beam size growth is not only for vertical direction, but also horizontal. > Since the horizontal IP profile is asymmetric shape, the correction with octupoles is not effective. > > Therefore, I think we had better to optimize the IP beam size without octupoles, > and the octupole should be used for the tail folding. > > Sincerely, > > Toshiyuki OKUGI, KEK > > > > > > ######################################################################## > Use REPLY-ALL to reply to list > > To unsubscribe from the ILC-BDS list, click the following link: > https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=ILC-BDS&A=1 ######################################################################## Use REPLY-ALL to reply to list To unsubscribe from the ILC-BDS list, click the following link: https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=ILC-BDS&A=1