IBS cannot be calculated after adding a certain number of wigglers.

[southwindow]

<t>Hello～<br/>
<br/>
I've recently been trying to see the effect of damping on IBS by adding wigglers one by one to a storage ring with long straight section, and the way I've done it is by replacing elements of drifts with wigglers. I could see the emittance decreasing as the number of wigglers increased, but after adding a certain amount of wigglers, the emittance jumped.<br/>
<br/>
I don't know if this is a bug. Attached is my lattice file and calculation results, and a Jupyter Notebook file that completes the replacement and calculation. <br/>
<br/>
Regards, <br/>
<br/>
Ao</t>

[michael_borland]

When I try your lattice, it gives undefined lattice functions for the vertical plane. If you are adding wigglers, the vertical tune will change and has probably moved too close to an integer or half-integer resonance.

--Michael

[southwindow]

Dear Michael,

Thank you very much for your reply! If I understand you correctly, you are saying that I need to adjust the strength of the quadrupole after each addition of the wiggler to make the vertical tune consistent right? Or is there any other way to avoid this problem?

Regards,
Ao

[michael_borland]

Ao,

Yes, that's right. As a quick workaround, you can set FOCUSING=0 on your WIGGLER elements, if that's how you are modeling them. You can to keep in mind that this is unphysical.

In some cases, all it takes to restore the lattice to a reasonably sane state is to correct the tunes, which is easily done with the &correct_tunes command.

-Michael