Simulation of coupled-bunch effects with a time-variant quadrupole

[Siwei_Wang]

Dear Michael,

Recently I'm trying to do a simulation of the coupled-bunch effects with a time-variant quadrupole in the lattice. The quadrupole strength varies in a harmonic of the revolution frequency to introduce a bunch-by-bunch tune spread that aims to cure coupled-bunch instability.

My first idea was to model the quadrupole and use the "&modulate_elements" command to change the strength with time and did several studies, and found that the tune between all the bunches is the same. After some digging I realized that the "&modulate_elements" command changes the strength of the quadrupole turn-by-turn, and couldn't show the different impact between bunches.
Do you have some ideas how I could model this time-variant quadrupole which is effective bunch-by-bunch?

Many thanks,
Siwei

[michael_borland]

Siwei,

I think the MRFDF (multipole rf deflector) element should do it. You can set up rf multipoles from dipole to decapole.

--Michael

[Siwei_Wang]

Hi Michael,

Many thanks for your reply. MRFDF works for me!

Best regards,
Siwei