4.18 define_field_sampling

• description: Requests sampling of the fields vs time or space coordinates. One may set up sampling of a specific field component along a line in z or r, with output vs the distance along the line at specified times or else output of the average value along the line vs time.
• example:
  &define_field_sampling  
      filename = "gunRun.Ez_t,  
      component = "Ez",  
      time_sequence = 1  
      direction = "z",  
      min_coord = 0, max_coord = 0.01,  
      position = 0,  
      time_interval = 10e-12,  
      start_time = 0,  
  &end

  Requests logging of E_z as a function of time, with samples made a 10ps simulated time intervals starting with the start of the simulation. The data output is the average of E_z along a line from z = 0 to z = 1cm.

• synopsis and defaults:
  &define_field_sampling  
      STRING filename = NULL;  
      STRING component = NULL;  
      STRING direction = NULL;  
      double min_coord = 0;  
      double max_coord = 0;  
      double position = 0;  
      double time_interval = 0;  
      double start_time = 0;  
      long time_sequence = 0;  
  &end

• details:
  • filename: Name of an SDDS file to which to write the data.
  • component: Field component to sample. Must be one of ”Ez”, ”Er”, ”Jz”, ”Jr”, ”Bphi”, ”Phi”, ”Ephi”, ”Bz”, ”Br”, and ”Q”. E is the electric field, B is the magnetic field, J is the current density, Phi is the scalar potential, and Q charge assigned to a grid point.
  • direction: The direction of the line along which samples are taken. Must be ”z” or ”r”.
  • min_coord, max_coord: The minimum and maximum coordinates of the sample line.
  • position: The position of the sample line in the direction orthogonal to direction.
  • time_sequence: Flag requesting that instead of writing the selected component as a function of the coordinate direction, spiffe instead write the average value of the component along the sample line as a function of time. It zero, then spiffe creates a new SDDS page for each sample time.
  • start_time: The simulated time in seconds at which to start sampling.
  • time_interval: The simulated time interval in seconds at which to make samples.