Is this a Bug?
Moderators: cyao, michael_borland
Is this a Bug?
I did a tracking of a simple lattice ,but the normalized emittance changed.Is this a bug? Can you have a look
- Attachments
-
- twi.png (8.24 KiB) Viewed 5976 times
-
michael_borland
- Posts: 1959
- Joined: 19 May 2008, 09:33
- Location: Argonne National Laboratory
- Contact:
Re: Is this a Bug?
It's not a bug, but rather a result of the fact that you plotted the uncorrected emittance and have dispersion in the system. The uncorrected emittance is defined as
ex = sqrt{ <x^2> <xp^2> - <x*xp>^2 }
If there is dispersion (e.g., following a dipole magnet), then this quantity can grow.
If you plot the corrected emittance (ecx or ecnx), you get a different picture. For the corrected emittance, we make the transformation
x -> x - delta*etax
xp -> xp - delta*etaxp
prior to computing the emittance.
As you can see in the attached plot, ecnx is nearly constant. It isn't exactly constant because of chromatic aberrations from the quadrupoles.
--Michael
ex = sqrt{ <x^2> <xp^2> - <x*xp>^2 }
If there is dispersion (e.g., following a dipole magnet), then this quantity can grow.
If you plot the corrected emittance (ecx or ecnx), you get a different picture. For the corrected emittance, we make the transformation
x -> x - delta*etax
xp -> xp - delta*etaxp
prior to computing the emittance.
As you can see in the attached plot, ecnx is nearly constant. It isn't exactly constant because of chromatic aberrations from the quadrupoles.
--Michael
- Attachments
-