Proton beam electromagnetic interactions with an RF cavity - analysis of wakefields*

Electromagnetic interactions of proton beams with RF cavities, also known as 'wakefields', affect dynamics of each particle and the collective beam dynamics [1]. Analytical techniques that are useful for computing wakefields in beampipes [2] are not applicable to resonant structures. Using FDTD calculations, time-varying electromagnetic fields induced by a single moving proton bunch are obtained.  A numerical Green’s function approach is proposed to account for the wakefields due to individual superparticles within a particle-in-a-box model. Further analysis of electromagnetic fields inside an RF cavity is done using their time-frequency representations. Preliminary analysis suggests that with the increase in the number of protons per bunch to the order of 10¹², or more, the wakefields in cavities may significantly affect beam dynamics.

References:

[1] Chao A.W., Physics of collective beam instabilities in high energy accelerators, Wiley, N.Y., 1993, 384 pp.

[2] Macridin, A., Spentzouris, P., Amundson J., “Impedances and wake functions for non-ultrarelativistic beams in circular chambers,” FERMILAB-PUB-12-518-CD, 1-14.