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Dear Glen, > 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. I checked the optics for your energy collimator design, and I understood that the strong defocusing magnet after bending magnets makes large dispersion. By using this optics, we can make a same dispersion with short length. The disadvantage of the optics, however, is the difficulty to make the large vertical beta function at energy collimator, and we must redesign the total betatron and energy collimator system in order to make the vertical collimator gap large. I think the most simple method to reduce the beamline length of the BDS is to reduce the maximum beam energy of BDS. When the beamline length is reduced by more than 200m only at the bending magnet for energy collimator and FFS, the maximum beam energy is reduced to 2/3 (600-700GeV) by keeping the amplitude of dispersion and the same chromatic aberration of SR. However, sine the chromaticity of each quadrupole is changed by this modification, we must redesign the FFS optics, and the design will spend a couple of months. But, this strongly depend on the political decision whether will we make a shorter BDS optics of small maximum energy or not. regards, Toshiyuki OKUGI, KEK ----- Original Message ----- 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 ######################################################################## 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