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 won’t 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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> On Apr 2, 2015, at 7:58 PM, Toshiyuki Okugi <[log in to unmask]> wrote:
>
>
> Dear Glen,
>
> I think it is possible to reduce the length of energy collimator
> for the horizontal emittance growth by the Synchrotron radiation.
>
> The problem is, however, the vertical betatron collimation is still remained.
> The gap of the vertical collimator is better to design as large as possible
> in order to reduce the wake effect and to reduce the tolerance of orbit adjustment.
>
> In my design, the main vertical betatron collimation
> is also assumed to the energy collimator section (highest betaY),
> and the vertical beta function at energy collimator is designed to betaY=4000m
> and the phase advance in between energy colliator to QD0 was adjusted
> in order to increase the collimator gap of the vertical spoiler.
>
> In present design, the vertical full gap hight is about 2mm,
> and the gap is comparable to the horizontal one at betatron collimator section.
>
> When we reduce the energy collimator length, the vertical beta function is also reduced (in generally).
> Therefore, the vertical beta collimation also should be set at betatron collimation section,
> and the gap of the collimator will be reduced to about half to the present one.
>
> This is just a comment for this issue.
>
> Sincerely,
>
> Toshiyuki OKUGI, KEK
>
>
> ----- Original Message -----
> Dear colleagues,
>
> As reported in the recent global timing working group report (EDMS D1097725), the BDS group was invited to look into ways to cut ~150m from the length of the positron system (optionally also from the electron side) to fix the timing mismatch between e- and e+ beams which exists in the current TDR lattices. There is a change request in process looking at increasing the linac length by ~1.5km (CR4 - EDMS D1092915) for additional reasons which will fix this problem if that is approved, but here Nick has also asked for a quick look into the possibility of shortening the BDS as an input into these discussions.
> I think the most obvious candidate is for shortening the energy collimation system, which comes mainly at the cost of an additional 2.1% horizontal emittance growth and 220 MeV energy loss for the 1 TeV machine (negligible impact for 500 GeV).
> As a suggested response to these requests, please find attached short note. Let me know if you have any comments or other suggestions on this topic.
>
> Best regards,
>
> - Glen.
>
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