Momentum Aperture without sextupole

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tiansk
Posts: 39
Joined: 16 Mar 2012, 22:01

Momentum Aperture without sextupole

Post by tiansk » 16 Jul 2018, 21:42

Dear All:

I want to tracking the Momentum Aperture for a lattice without sextupole to simulate the machine beam-tuning process.Without the sextupole,the chromaticity【dnux/dp (1/(2$gp$r)) = -2.159890e+02】and 【dnuy/dp (1/(2$gp$r)) = -2.921960e+02】 are so big!I used one particle tracking(by using the MALIGN element to set the initial DP),I get the particle with dp/p=0.013 could be survived for 10000 turns.But with the momentum_aperture command,I got that the deltaPositive is smaller than 4e-3,Particle lost with delta0 = -5.000000e-03.In the momentum_aperture command,I set forbid_resonance_crossing=0.
I used Accelerator Toolbox for the same lattice particle tracking,the particle with dp/p=0.013 could be survived for 10000 turns too!
I want to know the criterion for Particle lost in momentum_aperture command is same as track command?
Thanks in advance!
Tiansk
Attachments
dt vs dp.jpg
Momentum Aperture.jpg

michael_borland
Posts: 1772
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
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Re: Momentum Aperture without sextupole

Post by michael_borland » 17 Jul 2018, 15:55

Since you set forbid_resonance_crossing=0, the criterion for particle loss is the same as long as the lattice is the same. This result is certainly surprising. You should check that all physical apertures, rf settings, and synchrotron radiation settings are the same. If you can't locate the source of the discrepancy, please upload the files and I'll take a look.

--Michael

tiansk
Posts: 39
Joined: 16 Mar 2012, 22:01

Re: Momentum Aperture without sextupole

Post by tiansk » 18 Jul 2018, 00:10

Hi,Michael

I follow your advice to check all the settings,I found there is one point where the settings is different.In one particle tracking model,I set the MALIGN element with dx=0,dy=0 and dp=0.013,but in the momentum_aperture model,I set x_initial=1e-6,y_initial=1e-6.I think in the momentum_aperture tracking model,the ELEGANT using NAFF method to get the tunes,so I set a initial x or y offset,it may help to get the tunes.When I set x_initial=0e-6,y_initial=0e-6,the deltaPositive got from the momentum_aperture model is almost same like the one particle tracking model.I don't know why the Momentum Aperture is so sensitive to the initial offset(I think x_initial=1e-6 is small enough).

Best,
Tiansk

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