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.
>
>
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