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





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