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Dear Toshiyuki, Edu and all,

I notice your use of SD0 and SF1 in correction knobs- just a reminder that there is currently no provision for being able to independently change the offset of these two sextupole field positions in the baseline design as they are co-wound onto the QD0 tube in the 2 final doublet cryostats. Hopefully there are enough degrees of freedom just using the other 3 sextupoles for the required disp_x, disp_y, waist_x, waist_y and <x’y> linear knobs. If not, this will be important information for the FD design considerations.

Regards,

- Glen.

On Apr 6, 2015, at 8:29 PM, [log in to unmask] wrote:

Dear Edu,

In order to understand this issue, I wonder if in your lattice design 
process you use the FD octupole magnets.

Since the IP profile has almost no tail, 
and the core and rms beam size is consistent with the design (see the previous report),
the octupole should be no effect to the beam size for ECM=500GeV.

For ECM=250GeV, we have a possibility to recover the luminosity by 5% by using higher order correction.
But, since the beam size growths for horizontal and vertical are quite different properties,
it seems difficult to correct only with single knob.
Furthermore, the higher order correction has the disadvantage to decrease the collimation depth 
as I already pointed out.

Also regarding the errors, do you include errors from the movers (2um) 
in your simulation?

I did not put the mover error.

But, when the sextupole position is shifted by micron order,
the IP beam size is increased too much for the ILC FFS (see the attached file).
If the mover resolution was only 2um, we cannot see the IP beam size response by using the linear knob.
I wonder why the effect to your simulation is so small.

Furthermore, the effect of the mover resolution is linear optics deformation,
and it should be no effect to the octupole correction.

Anyway, I will evaluate the tolerance of the mover resolution
by the point of view of IP beam size tuning.
(I expect one order smaller than your evaluation.)

regards,

Toshiyuki OKUGI, KEK



On 04/06/2015 02:05 AM, Okugi, Toshiyuki wrote:

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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[log in to unmask]"><ILCsextupoleOffset.png>