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How to properly fiducialize an RFMODE element

Posted: 17 Oct 2021, 03:58
by duanz
Hi Michael,

I'm trying to simulate a bunch injecting into an empty booster. I use a two-page bunch distribution in the tracking, the first page is a single-particle bunch for fiducialization, so that the second page can be the real bunch with a specified temporal error. However, RFMODE seems to accumulate the beam-induced voltage of the single particle bunch in the first page, using the same bunch charge as the second page. This obviously is not what I want. What is your suggested way to treat this fiducialization issue? Thanks!



Re: How to properly fiducialize an RFMODE element

Posted: 15 Nov 2021, 12:52
by michael_borland

Sorry for the long delay in responding. I think you are trying to model the combination of transient beamloading and jitter when injecting into a ring. The way I'd do this is to send in a single bunch, but set the charge to a very low value and the timing offset to zero. Then, on the second pass, increase the charge to the desired value (using modulate_elements) and impart the timing error (using MALIGN,ON_PASS=2,...). In this way, the cavity is set up at the nominal voltage and phase, waiting for the beam to arrive.

If the beam has a large energy spread such that there is significant time-dispersal in one turn, you may want to perform an initial run to backwards track the beam through the ring one turn, then load the output of that run into your injection simulation.

An example is attached.


Re: How to properly fiducialize an RFMODE element

Posted: 16 Nov 2021, 20:04
by duanz
Thanks, Michael! This is exactly what I need.