4.2 Geometry File

• description: This page describes the structure of the geometry file used with the define_geometry namelist. The file is similar to those used with the program POISSON.
• example:
  ! new RF gun, first cell  
   &po x=0.000, y=0.000 &end  
   &po x=0.000, y=0.006 &end  
   &po x=0.0016, y=0.0135 &end  
   &po x=0.0016, y=0.0427755  &end  
   &po x=0.0060, y=0.0427755   &end  
   &po nt=2, x0=0.006, y0=0.0181355,  
             r=0.02464, theta=0.0  &end  
   &po x=0.03064  , y=0.014818    &end  
   &po nt=2, x0=0.02861, y0=0.014818,  
             r=0.00203, theta=-90.0  &end  
   &po x=0.02836, y=0.012788   &end  
   &po nt=2, x0=0.02836, y0=0.010588,  
             r=0.0022, theta=180.0  &end  
   &po x=0.02616, y=0.01008     &end  
   &po nt=2, x0=0.03116, y0=0.01008,  
             r=0.005, theta=270.0  &end  
   &po x=0.0348, y=0.00508  &end  
   &po x=0.0348, y=0.00  &end  
   &po x=0.000000, y=0.00  &end

• synopsis and defaults:
  &point  
      int nt = 1;  
      double x = 0;  
      double y = 0;  
      double x0 = 0;  
      double y0 = 0;  
      double r = 0;  
      double a = 0;  
      double b = 0;  
      double aovrb = 0;  
      double theta = 0;  
      int change_direction = 0;  
      double potential = 0;  
      int ramp_potential = 0;  
      int material_id = 0;  
  &end

• details:
  • nt: The segment type, where 1 (the default) indicates a line segment; 2 indicates an arc of a circle; 3 indicates the start of a separate structure; and 4 indicates a definition of an in-vacuum point.
  • x, y: For nt=1, the endpoint of the line. x corresponds to z (the longitudinal coordinate) and y corresponds to r (the radial coordinate). For nt=2, the endpoint of the circular or elliptical arc relative to (x0, y0). For nt=3, the first point on the new shape. For nt=4, the coordinates of the in-vacuum point.
  • x0, y0: For nt=2, the center of the circular or elliptical arc.
  • r: For nt=2, the radius of the circular arc. The equation of the arc is (x-x₀)²+(y-y₀)² = r².
  • a, b, aovrb: For nt=2, the parameters of the elliptical arc. The equation of the arc is (x-x₀)²∕a² + (y -y₀)²∕b² = 1. If a or b is zero, then the value is determined using the ratio aovrb (a over b).
  • theta: For nt=2, the angle in degrees of the end of the arc as seen from the center of the arc. If this angle is less (greater) than the angle of the starting point (which is on [-180,180]), then the sense of the arc is clockwise (counter-clockwise).
  • change_direction: For nt=2 when theta is not given but x and y are, spiffe may have trouble determining the direction of the arc. This flag can be used to change the direction.
  • potential: The potential of the segment, in volts.
  • ramp_potential: If non-zero, the potential along a line is ramped linearly between the given value and the end value for the previous segment. Only implemented for nt=1.
  • material_id: a positive integer that identifies the material of which this segment is made. Used to associate segments of the geometry with primary emission (define_emitter) and secondardy emission (define_secondary_emission).