Hi,
When I run a beam with CSR I can see orbit excursions (Cx and Cy) through bunch compressors due to particles losing energy in a dispersion region and then betatron oscillating. When I turn the charge to zero (i.e. no CSR), I still see remnant excursions in Cx and Cy. Granted, they are orders of magnitude less, but I'd like to know how to interpret them. It's not clear to me what process could be causing it.
Thanks,
chris
Understanding Cx and Cy
Moderators: cyao, michael_borland
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Re: Understanding Cx and Cy
Chris,
How large are the values?
Have you tried increasing the N_KICKS parameter?
--Michael
How large are the values?
Have you tried increasing the N_KICKS parameter?
--Michael
Re: Understanding Cx and Cy
Michael,
The values peak at +/-2e-04 m. I changed all the CSRCSBENDs to SBENDs and the centroid positions do not change.
--chris
The values peak at +/-2e-04 m. I changed all the CSRCSBENDs to SBENDs and the centroid positions do not change.
--chris
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- Posts: 1951
- Joined: 19 May 2008, 09:33
- Location: Argonne National Laboratory
- Contact:
Re: Understanding Cx and Cy
Chris,
This seems odd. Can you post the files or send them to me via email.
--Michael
This seems odd. Can you post the files or send them to me via email.
--Michael
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- Posts: 1951
- Joined: 19 May 2008, 09:33
- Location: Argonne National Laboratory
- Contact:
Re: Understanding Cx and Cy
Chris,
Thanks for sending the lattice file.
This appears to be a result of nonlinearities in the transport. If I take your lattice that uses SBENs, and set default_order=1 in &run_setup, I don't see the variation of Cx or Cy. If I set default_order=2, I see it. I also see considerable growth in the emittances (looking at ecnx and ecny from the sigma output of &run_setup), which also indicates strong nonlinearities.
You can easily see how this might happen. Suppose there is a quad of focal length f in a region where the dispersion is eta. The horizontal coordinates of the particles at the quad entrance are x=delta*eta. The kick to each particle is dx' = -x/f/(1+delta), which to second order is dx' = -(delta*eta/f)*(1-delta). Clearly, <dx'> = <delta^2>*eta/f, resulting in a non-zero centroid kick if the energy spread is non-zero.
--Michael
Thanks for sending the lattice file.
This appears to be a result of nonlinearities in the transport. If I take your lattice that uses SBENs, and set default_order=1 in &run_setup, I don't see the variation of Cx or Cy. If I set default_order=2, I see it. I also see considerable growth in the emittances (looking at ecnx and ecny from the sigma output of &run_setup), which also indicates strong nonlinearities.
You can easily see how this might happen. Suppose there is a quad of focal length f in a region where the dispersion is eta. The horizontal coordinates of the particles at the quad entrance are x=delta*eta. The kick to each particle is dx' = -x/f/(1+delta), which to second order is dx' = -(delta*eta/f)*(1-delta). Clearly, <dx'> = <delta^2>*eta/f, resulting in a non-zero centroid kick if the energy spread is non-zero.
--Michael
Re: Understanding Cx and Cy
Michael,
Thanks for the explanation. That makes sense.
--chris
Thanks for the explanation. That makes sense.
--chris