I calculated the bunch-by-bunch positron current dependence
and the dynamic aperture of this 14kg_021805 lattice
in a 9x4 configuration
and compared them to the calculations for the
lattice now in use for HEP, hibetainj_20040628.
I turned the effect of the beam-beam interaction
at the IP off for this comparison. The tunes are held
independent of positron current at h/v=0.518/0.577.
First we can see that the bunch
length is decreased as desired from 11.3 mm to 8.8 mm:
14kg:
http://www.lns.cornell.edu/~critten/cesr/injection/notes/22feb05/bunch_660/P014.html
hibetainj:
http://www.lns.cornell.edu/~critten/cesr/injection/notes/12jan05/bunch_602/P014.html
The energy spread is reduced from 0.85e-3 to 0.65e-3, as intended.
14kg:
http://www.lns.cornell.edu/~critten/cesr/injection/notes/22feb05/bunch_660/P013.html
hibetainj:
http://www.lns.cornell.edu/~critten/cesr/injection/notes/12jan05/bunch_602/P013.html
The horizontal emittance is reduced from 140 nm to 110 nm, increasing
only moderately with positron current in both cases:
14kg:
http://www.lns.cornell.edu/~critten/cesr/injection/notes/22feb05/bunch_660/P011.html
hibetainj:
http://www.lns.cornell.edu/~critten/cesr/injection/notes/12jan05/bunch_602/P011.html
The maximum horizontal beta blows up from 45 m to 50 m at 2 mA in the old lattice
and from 41 to 47 m in the new lattice:
14kg:
http://www.lns.cornell.edu/~critten/cesr/injection/notes/22feb05/bunch_660/P003.html
hibetainj:
http://www.lns.cornell.edu/~critten/cesr/injection/notes/12jan05/bunch_602/P003.html
The dynamic aperture calculations expressed in units of beam RMS size show the
new lattice to be slightly worse (8 sigma rather than 10 sigma at 2 mA):
14kg:
http://www.lns.cornell.edu/~critten/cesr/injection/notes/22feb05/dynap_660/P007.html
hibetainj:
http://www.lns.cornell.edu/~critten/cesr/injection/notes/12jan05/dynap_605/P007.html
There IS one remarkable quality to the new lattice, which is that the vertical beta*
appears to depend on positron current much differently bunch-to-bunch than it
did in the old lattice, but this dependence is at the percent level. The value
of beta_v* is about 15% lower in the new lattice (9.6 mm rather than 11.4 mm):
14kg:
http://www.lns.cornell.edu/~critten/cesr/injection/notes/22feb05/bunch_660/P016.html
hibetainj:
http://www.lns.cornell.edu/~critten/cesr/injection/notes/12jan05/bunch_602/P016.html
In general I conclude from these results that the new lattice fulfills the
requirement of shorter bunch length and reduced energy spread without making
the parasitic BBI effects much worse.
It also does not show the remarkable, and I suspect desirable, characteristic
of the recent wiggler-15-off lattice design whereby the BBI effects were very similar
for all the bunches.
-- jim
========================================================
James Crittenden Tel. (607) 255-9424
Wilson Synchrotron Laboratory Fax (607) 255-8062
Cornell University
Ithaca, New York 14853-8001
========================================================
David Rubin wrote:
> Gentlemen,
> We ran the beam beam simulation for the 14kg optics at 4 different
> currents.
> At each current we track for 10 damping times (400k turns). The results are
> here
http://www.lns.cornell.edu/~dlr/beambeam/131204-1_020405_021805.gif
>
> There are calculations for 3 different optics in the plot
>
> hibetainj_20040628 is the 21kg optics we are using now
> bmad_14kg_021805 is the 14kg lattice
> hibetainj_nosol_v01 is the solenoid off version of the 21kg lattice
>
>
> You see that there is not much difference between the 14kg and 21kg
> luminosity.
> Perhaps the luminosity for the 14kg is 5-10% higher.
>
> So I am not as enthusiastic about the 14kg optics as I was in our last
> machine studies
> meeting and am happy to reconsider ms plans for this week.
>
> Or maybe we should proceed as planned since
> a) 5-10% may be worth the effort.
> b) The simulation may be wrong
> c) We will learn something about low field behavior of the wigglers
>
> Dave
--
