EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH

RF Cavity

label: RFCAVITY, L=real,VOLT=real,LAG=real,HARMON=integer,FREQ=real;
                  

• L: The length of the cavity (DEFAULT: 0 m)
• VOLT: The peak RF voltage (DEFAULT: 0 MV). The effect of the cavity is

  delta(E) = VOLT * sin(2 pi * (LAG - HARMON * f₀ t)).

• LAG: The phase lag [2pi] (DEFAULT: 0).
• FREQ: The frequency [MHz] (no DEFAULT). Note that if the RF frequency is not given, it is computed from the harmonic number and the revolution frequency f₀ as before. However, for accelerating structures this makes no sense, and the frequency is mandatory.
• HARMON: The harmonic number h (no DEFAULT). Only if the frequency is not given.
• Please take note, that the following MAD8 attributes: BETRF, PG, SHUNT and TFILL are currently not implemented in MAD-X!<
• Note as well that twiss is 4D only. As a consequence the TWISS parameters in the plane of non-zero dispersion may not close as expected. Therefore, it is best to perform TWISS in 4D only, i.e. with cavities switched off. If 6D is needed one has to use the ptc_twiss command.

• n_bessel (DEFAULT: 0):

  Transverse focussing effects are typically ignored in the cavity in MAD-X or even PTC. This effect is being calculated to order n_bessel, with n_bessel=0 disregarding this effect and with a correct treatment when n_bessel goes to infinty.

• no_cavity_totalpath (DEFAULT: no_cavity_totalpath=false):

  flag to choose if in a cavity the transit time factor is considered (no_cavity_totalpath=false) or if the particle is kept on the crest of RF voltage (no_cavity_totalpath=true).

Example:

BEAM,PARTICLE=ELECTRON,ENERGY=50.0;
CAVITY:   RFCAVITY,L=10.0,VOLT=150.0,LAG=0.0,HARMON=31320;