dynamic aperture after insert a wiggler

[Samira.kasaei]

Dear Michael,

I inserted a wiggler in my ring and after optimization the beam optics, I checked dynamic aperture.
Dynamic aperture before insertion a wiggler was 0.2 horizontally and 0.04 vertically while it was decreased to 0.04 horizontally and 0.008 vertically.
Do you think if I had a mistake to find dynamic aperture?

Many thanks and best regards,
Samira

[Samira.kasaei]

Dear Michael,

Concerning my previous post, first I wanted to be sure that I didn't have a mistake.
Then If my run was correct , what can I do to increase dynamic aperture?

Many thanks and best regards,
Samira

[michael_borland]

Samira,

If I turn off the wiggler by setting FIELD_FACTOR=1e-10 on the UKICKMAP element, I don't see much difference in the DA. Perhaps there is some other change between your two results.

I noticed a few things about your simulations that might warrant attention:

• The chromaticities are both negative (about -4.6).
• You are dividing the elements, but using few slices for the CSBEND elements. This will make the simulation slower. I recommend against dividing elements unless you need the resolution for loss recording.
• You are using the default fourth-order integrator. You can save time with the sixth-order integrator and fewer slices. See attached.

--Michael

[Samira.kasaei]

Dear Michael,

I checked with accelerator toolbox and chromaticity must be +6 and+7. but as you mentioned chromaticity values given by elegant is -4.6.
Do you know the reason?

Many thanks for your answer,
Samira

[Samira.kasaei]

Dear Michael,

Here is my lattice with the affect of fringe field.
I do appreciate if you can take a look to my files.

Best regards,
Samira

[michael_borland]

Samira,

I don't have an explanation for why the chromaticity is not what you expect. The lattice definition seems fine. (I would recommend EDGE1_EFFECTS=EDGE2_EFFECTS=4 and FSE_CORRECTION=1 on the CSBEND elements, to get the best dipole fringe model.)

I tried computing the chromaticity using tracking and it agrees very well with the values reported by &twiss_output.

Elegant and AT agree quite well on the chromatic of the APS-U lattice, which has many strong gradient dipoles. However, the bending radius is about 5x larger than yours.

I did notice that if I double the strength of both sextupole families, the chromaticities are both positive, with x=6.4 and y=5.8. Is it possible the strengths were translated incorrectly?

--Michael

[Samira.kasaei]

Dear Michael,

I tried with twice values with Elegant and I got the same chromaticity as yours. but our storage ring is operating at the chromaticity of 6 and 7 with sextupole gradients of 10.98 and -16.57.

I do appreciate all of your answers in this issue,
samira