Simulation of transverse multi-bunch instability using the LRWAKE element

[xhs05]

To whom it may concern,

Hi!

Sorry that I've cleared the bug in my scripts. The error is because the input file for the LRWAKE element has all zero values. After generating the correct sdds file as input for LRWAKE, the scripts work properly.

Regards,
Haisheng

[michael_borland]

Haisheng,

Thanks for letting us know.

--Michael

[Akhyani]

Dear Michael and all,

I am studying short-range and long-range resistive wall effects in our ring. I used trwake element for calculating short-range effects and I saw the instability around 0.7 mA for single-bunch tracking in zero chromaticity. While using lrwake element for multi-bunch tracking, I expected that the instability threshold will be approximately 100 mA (number of bunches*0.7 mA), but I didn't see any instabilities even at 400 mA. I was wondering what is wrong in my simulations?
Any help would be appreciated. I attached the lattice, bunch and the wake file.

Bests,
--Mina

[Akhyani]

Any ideas???

[lindberg]

I wasn't able to parse the attached files, so I'm not completely sure what you're doing here. Based solely upon your description, though, it sounds like you are using the same wakefield file for short- and long-range stability simulations. However, since the instability mechanism is quite different in these two cases one does not expect the thresholds to be the same. What I think you should be doing is continuing to use your short-range wakefield in the TRWAKE element regardless of the number of bunches, and then add on an additional LRWAKE associated with whatever long-range forces you expect. In other words, TRWAKE only affects particles within a given bunch, while LRWAKE only acts on trailing bunches. Hope this helps...

[SDastan]

Dear all,

In the instruction of the LRWAKE, there is something that I don't understand.

Untitled.png (7.95 KiB) Viewed 7252 times

Why the XFACTOR should multiply in longitudinal wake and ...? Is it true or it is just a mistype? Thanks in advance.

Regards,

[michael_borland]

Yes, those descriptions are all mixed up. XFACTOR, YFACTOR, and ZFACTOR multiply the horizontal, vertical, and longitudinal wakes, respectively.

Thanks for pointing out the error.

--Michael