Preloading when using n_cavities on RFMODE

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Teresia
Posts: 30
Joined: 04 Oct 2018, 08:42

Preloading when using n_cavities on RFMODE

Post by Teresia » 02 Jun 2021, 10:50

Hi,

I'm wondering why the n_cavities parameter in RFMODE isn't taken into account when preloading the cavity? I have 8 main cavities, but when looking at the parameters for the preloading they only correspond to a single cavity? If I understand the source code correctly that is the case and n_cavities is only taken into account when calculating the energy gain.

Then I'm also wondering if the v_setpoint should be set to the voltage per cavity when using n_cavities or the total voltage for all cavities together? For my case I can get the beam to be stable with RF feedback if I put n_cavities = 1, the shunt impedance equal to the total impedance of all cavities, and v_setpoint equal to the total voltage for all cavities, but if instead change to n_cavities = 8 and the shunt impedance for a single cavity the beam is lost, but perhaps that is because I also need to change the v_setpoint to be the voltage per cavity instead?

Best regards,

Teresia

michael_borland
Posts: 1801
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
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Re: Preloading when using n_cavities on RFMODE

Post by michael_borland » 11 Jun 2021, 18:40

Teresia,

The best way to understand the N_CAVITIES parameter is that it simply models the effect on the beam of N identical cavities. All settings and parameters must be relevant to a single cavity. The single cavity is modeled, but its effect is applied to the beam N times. The assumption is implicitly made that the beam longitudinal distribution doesn't change significantly from one cavity to the next.

--Michael

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