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Dear Toshiyuki, Thanks for your comments: With regards to the upstream energy spectrometer: The requirements to have this system I think are well understood and nobody, as far as I am aware, is suggesting that we remove it. For the energy collimator design with shorter length: the energy collimator also contains 6 quadrupole magnets, here I chose to keep the (shortened) bend magnets at their existing design fields and use the quadrupoles to keep the central design dispersion in addition to matching the beta functions. Regards, - Glen. > On Apr 4, 2015, at 12:33 AM, Okugi, Toshiyuki <[log in to unmask]> wrote: > > > Dear Glen, > > I have a comment about the idea to remove the upstream energy spectrometer. > The chicane of the upstream energy spectrometer has 3 roles. > > 1) Energy monitoring to abort the beam, when the beam energy drop was observed. > Therefore, the energy spectrometer should be arranged to the upstream of the beam abort line. > > 2) Beam line shift from original beam line to detect the signal of laserwire. > Therefore, we must shift the beam line more than 10mm (the design is 20mm), > when the inner diameter of chamber was 20mm. > > 3) Spent electron measurement for polarimeter. > It is important to measure the large energy spectrum to evaluate the polarization. > When we use the 20mm diameter of the beam pipe, > the chicane with 20mm dispersion can be measure the spent electron with the beam energy of E<2*Ebeam/3. > On the other hand, the energy range was reduced to E<Ebeam/3 for the 5mm dispersion chicane. > The chicane with large dispersion is better for the polarization measurement. > Furthermore, we can measure the dispersion with the beam tuning dump in beam commissioning > by putting the polarimeter to the upstream of the tuning dump line. > > I think the chicane with 20mm dispersion for energy spectrometer and polarimeter > is important for ILC BDS. > > > Furthermore, I have a question of your energy collimator design. > the dispersion, generated by bending magnet is roughly defined to "eta=L*theta/2". > > The half length of ILC energy collimator is roughly 200m > and the total bending angle to the center is 1.25mrad. > The evaluated dispersion by the simple formula is 125mm. > The dispersion of the energy collimator is 150mm, and number is consistent with the rough evaluation. > > In generally, when the length of energy collimator is changed, > we must increase the total bending angle to make same dispersion at the energy collimator. > > How to increase the dispersion at the center of the energy collimator? > If the bending angle was increased to make the dispersion large, > the tunnel layout also must be changed. > > with best regards, > > > Toshiyuki OKUGI, KEK > > > ----- Original Message ----- > Thanks Toshiyuki, I have added a statement that the reduced vertical beta function may adversely impact the collimation efficiency and possibly increase wakefield sensitivity under case 2 and in the summary. Before we would implement this change (which hopefully we wonąt need to), we would obviously have to consider this point in light of a requirements document for the collimation system, which we would hopefully have had time to write by then. > > Cheers, > > - Glen. > > > ######################################################################## > 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