harmonic cavity with voltage lower than radiation loss/turn

[asaa]

Hi Michael,
Tracking in a ring seems to fail when a harmonic cavity with a voltage lower than the radiation loss per turn is included. In such a case the phase of the harmonic cavity is not well calculated by the rf_setup command. We “solve” it by putting a dummy voltage value on the rf_setup and later using the alter_element command to put the right voltage just before tracking (see attached). Could you have a look at it?
(In versions 25.1 and earlier this problem did not appear as the voltage did not have to be explicitly included in the rf_setup command)
Many thanks!
Angela

[michael_borland]

Angela,

The rf_setup command doesn't include any effects other than the main rf cavities and synchrotron radiation. If you want to use rf_setup just to set the frequency, you can then set the voltage and phase "by hand" with alter_elements.

For setup of double-rf systems for bunch lengthening, the script "longitCalcs" will help. It should be available if you have the latest version of elegant. (Also, if you use my Android app TAPAs, you'll be able to do such calculations.) The 29.0.2 release of elegant (just posted) includes an upgrade to longitCalcs that will prepare an input file for use in elegant, to set up the cavities.

--Michael