rf_setup

• type: setup/action command.
• function: set up rf cavity frequency, phase, and voltage for a storage ring

&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;
&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.

• 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.
  

  $$\left(\frac{\Delta p}{p}\right)_{\rm bucket} = \sqrt{\frac{U_0}{\pi \alpha h E}}\sqrt{F(q)},$$ (3)

  
  
  where $U_0$ is the energy loss per turn, $\alpha$ is the momentum compaction factor, $h$ is the harmonic, $E$ is the beam energy,
  

  $$F(q) = 2 \left(\sqrt{q^2-1} - \arcsin \frac{1}{q}\right),$$ (4)

  
  
  and $q$ is the overvoltage factor, related to the rf voltage by $q = V/U_0$. (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.