-----Original Message-----
From: NAPOLY Olivier DAPNIA [mailto:olivier.napoly@cea.fr] 
Sent: Tuesday, November 22, 2005 4:46 AM
To: Bambade; Angal-Kalinin, D (Deepa); Grahame Blair; Jackson, F (Frank); Keller, Lewis P.
Cc: Seryi, Andrei; PAYET Jacques SMTP; RIPPON Cyril DAPNIA; Tomoyuki SANUKI; T.Tauchi
Subject: RE: [bds 203] Re: BDS-BCD ranking

 
Dear Colleagues

Attached are the results of our investigations concerning the stability of
the collisions in the head-on scheme revisited by Lew.

We have considered the following optics and parameters:
   - last quadrupole + sextupole doublets from 20 mrad SLAC FFS
   - 25 m of electrostatic separator @ 25 kV/m from 10.5 m to 35.5 m for a
total horizontal deflection angle of 0.5 mrad
   - 300 ns bunch separation, hence a parasitic kick at 45 m from the IP
   - 553 x 5 nm spot sizes at the IP (TESLA TDR)

The transverse separation with the above parameters is 10.97 mm (say 11 mm).

We have calculated the degradation of the luminosity (y-axis, in the plots)
due to the parasistic crossings in addition to the expected luminosity loss
due to bunch to bunch vertical jitter at the IP (x-axis in the plots), for a
train of 2800 bunches.

Our conclusion is that the current scheme is stable.
As you can see on these plots, the unstable regime start below 8.5 mm
transverse separation.

A 20 m long separator with 32 kV/m increases the transverse separation if it
starts at the same position. The current 'nominal' ILC beam parameters are
slightly more stable than the above.

We will write a note about these results shortly.

         Amitiés

                                                Olivier NAPOLY


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