7.54 rf_setup
- type: setup/action command.
- function: set up rf cavity frequency, phase, and voltage for a storage ring
- sequence: must follow run_setup. In action mode, must follow action-mode instance of
twiss_output.
- Command syntax, including use of equations and subcommands, is discussed in 7.2.
&rf_setup
STRING filename = NULL;
STRING name = NULL;
long start_occurence = -1;
long end_occurence = -1;
double s_start = -1;
double s_end = -1;
long set_for_each_step = 0;
double near_frequency = 0;
long harmonic = -1;
double bucket_half_height = 0;
double over_voltage = 0;
double total_voltage = 0;
long disable = 0;
long output_only = 0;
long track_for_frequency = 0;
&end
This command must follow a twiss_output command that includes radiation integral
computation, since the energy loss per turn is needed to set up the rf cavities. Note that the
command includes features to allow selecting a subset of the RFCA elements in the beamline. The
selected subset is assumed to include all of the cavities that will impart net energy to the
beam.
This command stores values for bunch length in symbols Sz0 and St0, and also stores the fractional
energy spread in Sdelta0, where they can be used in rpn expressions in subsequent commands,
e.g.,
&bunched_beam
sigma_dp = "(Sdelta0)",
sigma_s = "(Sz0)",
...
&end
If performing rf setup in the presence of a non-zero orbit, the best procedure is to run rf_setup twice,
in a sequence like the following
...
! Compute nominal radiation integrals
&twiss_output
radiation_integrals = 1
&end
! Perform nominal rf cavity setup
&rf_setup
name = *,
harmonic = 1296
total_voltage = 9e6
&end
! Set up to compute the closed orbit, which may depened on radiation losses and rf cavity location
&closed_orbit
output = %s.clo
&end
! Set up to compute twiss parameters and radiation integrals
&twiss_output
filename = %s.twi
radiation_integrals = 1
output_at_each_step = 1
&end
! Set up to perform rf cavity setup
&rf_setup
filename = %s.rf
name = *,
harmonic = 1296
total_voltage = 9e6
set_for_each_step = 1
&end
...
- filename — Name of a file to which data related to the rf settings will be written.
- name — A possibly-wildcard-containing string giving the names of the elements to set. If not
given, all RFCA elements are selected.
- start_occurence, end_occurence — If nonzero, these give the starting and ending
occurrence numbers of elements that will be set.
- s_start, s_end — If non-negative, these give the gaving and ending position limits for the
end-of-element locations of elements to be set.
- set_for_each_step — If nonzero, then the setup is repeated at each simulation step. In this
case, one must also give output_at_each_step=1 for twiss_output.
- near_frequency – If nonzero, then the rf frequency is chosen to be the closest harmonic to
the given frequency.
- harmonic — If nonzero, then the rf frequency is set to the given harmonic of the revolution
frequency.
- bucket_half_height — If nonzero, the voltage is computed so as to give the specified bucket half
height.
 | (11) |
where U0 is the energy loss per turn, α is the momentum compaction factor, h is the harmonic, E is
the beam energy,
 | (12) |
and q is the overvoltage factor, related to the rf voltage by q = V∕U0. (See Wiedemann, Vol. 1,
8.2.2.)
- over_voltage — If nonzero, the voltage is set to the given factor relative to the energy loss per
turn.
- total_voltage — If nonzero, the total rf voltage is set to the given value. The frequency and phase
are computed for this voltage.
- disable — If nonzero, command does nothing.
- output_only — If nonzero, command generates output file but does not change rf cavity
settings.
- track_for_frequency — If nonzero, particle tracking is used to determine the rf frequency. If zero,
the ideal length of the lattice is used.