Orbit correction with errors

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Cai_Meng
Posts: 17
Joined: 19 Jun 2017, 08:01

Orbit correction with errors

Post by Cai_Meng » 29 Jun 2017, 09:54

Dear Michael,

When I want to correct orbit with errors, I find the closed orbit is unreasonable large (.clo), however the max position and max kick strength (.scor) is good. The closed orbit and the beam center (.cen) is very large even at the BPMs. The simulation results are not self-consistent. At first, I think it's maybe because the position of BPMs and correctors are not reasonable. But I try some different cases, it doesn't work. So I run the elegant example "multiStepErrors1" and repacle the "n_steps=1" with "n_steps=100". The simulation results of beam center(.cen) and closed orbit (.clo) are large too. I think maybe some settings are not reasonable in my case, so I attached the files, could you please help me to check it and give me some suggestions? Thanks in advance!

Best regards,
Cai
Attachments
Run_step2.ele
(2.49 KiB) Downloaded 554 times
Lattice_Booster_V2.lte
(2.58 KiB) Downloaded 544 times

michael_borland
Posts: 1796
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
Contact:

Re: Orbit correction with errors

Post by michael_borland » 17 Jul 2017, 20:20

Cai,

I see two issues in your input files:
1. You are using the TILT parameter on the CSBEND elements, which changes the geometry. You should use the ETILT parameter for Error TILTs.
2. You did not set center_on_orbit=1 in the &track command. Without this, the beam is has initial coorindates of x=xp=y=yp=delta=0, which means it oscilates about the closed orbit rather than riding on it.

Also, when plotting, be aware that the orbit output file (step3.orb in your case) as orbits from before and after correction. After making the above changes and rerunning, try the following

Code: Select all

sddsprocess step3.orb step3.orbcor -match=param,Stage=corrected
sddsplot -split=page -sep=page -group=page -graph=line,vary  -same -col=s,x step3.orbcor  -col=s,Cx step3.cen
--Michael

Cai_Meng
Posts: 17
Joined: 19 Jun 2017, 08:01

Re: Orbit correction with errors

Post by Cai_Meng » 10 Aug 2017, 08:43

Dear Michael,

Thank you for your detailed replay and it's very helpful.

Best regards,
Cai

Cai_Meng
Posts: 17
Joined: 19 Jun 2017, 08:01

Re: Orbit correction with errors

Post by Cai_Meng » 29 Mar 2018, 10:11

Dear Michael,

There is one very strange question: in one simulation about closed orbit correction, I set the n_steps=500, every time all simulation resutls are very good until the 201-st seed can't find closed orbit and the elegant exit , show the information as following:

tracking step 201.0
reduced iteration fraction to 4.500000e-01
error: closed orbit did not converge to better than 1.464816e-02 after 400 iterations (requirement is 1.000000e-08)
Trying secondary, tracking-based method for orbit determination (50 turns).
reduced iteration fraction to 2.250000e-01
error: closed orbit did not converge to better than 1.631523e-02 after 400 iterations (requirement is 1.000000e-08)
plane iter rms kick rms pos. max kick max pos.
mrad mm mrad mm
------- ---- ---------- --------- ---------- ----------
48 H correctors set to zero
32 V correctors set to zero
error: closed orbit did not converge to better than 3.400094e-02 after 400 iterations (requirement is 1.000000e-08)
Trying secondary, tracking-based method for orbit determination (50 turns).
error: closed orbit did not converge to better than 2.873619e-02 after 400 iterations (requirement is 1.000000e-08)
Failed to find closed orbit.
Horizontal correction has failed.
warning: orbit correction failed--continuing with next step
0 matrices (re)computed after correction
error: closed orbit did not converge to better than 2.066307e-02 after 400 iterations (requirement is 1.000000e-08)
Trying secondary, tracking-based method for orbit determination (50 turns).
error: closed orbit did not converge to better than 1.715796e-02 after 400 iterations (requirement is 1.000000e-08)
periodic Twiss parameters (chromaticity valid for fully second-order calculation only!):
beta alpha nu eta eta' dnu/d(dp/p) dbeta/(dp/p) accept.
m 1/2pi m 1/2pi m mm-mrad
--------------------------------------------------------------------------------------------------------------------
x: -nan(ind) -nan(ind) nan -nan(ind) -nan(ind) -nan(ind) -nan(ind) 0.000000e+00
y: -nan(ind) -nan(ind) nan -nan(ind) -nan(ind) -nan(ind) -nan(ind) 0.000000e+00

Rf setup: frequency is 4.997995391649305e+08 Hz (h=756)
Voltage per cavity is 1.333333333333333e+06 V, phase is -nan(ind) deg

I want to look at what happens on this case, can i get the random seed of the 201 seed or how can i get the errors settings? Maybe i can set the closed_orbit_accuracy to 3e-2, but it is some big? Could you give me some suggestions or solution?

Thank you very much!

Best regards,
Cai

michael_borland
Posts: 1796
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
Contact:

Re: Orbit correction with errors

Post by michael_borland » 30 Mar 2018, 15:28

Cai,

You can use the error_log parameter of the &error_control command to request a log of the errors assigned to various elements. You can then load the page in question with the &load_parameters command in a new run, to understand in more detail what's gone wrong.

--Michael

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