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How to Specify a Grid

 

For the output of 2-dimensional ionization and characteristic x-ray distributions, a rectangular, not necessarily equidistant, grid is needed. This grid is used for the visualization of the aforementioned quantities on the screen using the SCREEN variable and the output to binary files by means of using the PMSAV variable (see Chapter 6.7 and 9.9).

SESAME supports two possibilities to generate this grid on your geometry. If no file name for a grid file is specified in the input deck by means of the CGRDFL variable in the &OUTPUT mamelist (see Chapter 9.9) then a grid is automatically generated by SESAME. This ''auto-grid'' is a quasi-equidistant grid with 66*66 grid points in the (x,z) plane. The non-equidistancy might be introduced because geometry points (vertices) are automatically taken as grid points. The auto-grid will not necessarily cover the whole geometry - the expansion is automatically chosen in that way that all requested events (ionizations) will lie in the grid area with a very high degree of confidence.

The second option is to specify a user-defined grid. To do so observe the following instructions:

  1. Specify a grid file name in the input deck using the CGRDFL variable of the &OUTPUT record (see Chapter 9.9), for instance: CGRDFL='EXA1.GRD'
  2. The grid file must contain the following grid specification. Each entry has to be written on a separate line. Between two reference points, the grid is equidistantly generated with the specified number of grid lines in this interval. The total number of grid lines in x and z directions are:

This input leads to the following structure:

          NINT_X
            GPX_1
              NGDXL_1
            GPX_2
              NGDXL_2
            GPX_3
              NGDXL_3
            .
            .
            .
              NGDXL_NINT_(X-1)
            GP_NINT_X
              NINT_Z
            GPZ_1
              NGDZL_1
            GPZ_2
              NGDZL_2
            GPZ_3
              NGDZL_3
            .
            .
            .
              NGDZL_NINT_(Z-1)
            GPZ_NINT_Z

Note: The units of coordinates must be in Å

Following an example of a grid file ( EXA1.GRD) for the simulation geometry file used in Chapter 6.6 is given. Considering, for instance, that only the tungsten signal from region I and the Oxygen signal from region III (only bulk part) is of interest and further taking into account the expected x-ray distribution and the shape of these regions, an appropriate grid file may look as follows:

    5
          0.0
          2
        500.0
          3
        800.0
          6
       1000.0
          7
       1500.0
    3
          0.0
         10
        500.0
          6
       1000.0
Note: The maximum overall number of gridlines in either directions is 66!

In x-direction five reference points are defined. With the specified lines between these reference lines 23 grid lines are defined. In z-direction three reference points are defined, which leads together with the lines between the reference lines to 19 grid lines in the z direction.

Figures 6.9 and 6.10 show the auto-grid for two different acceleration energies (2 and 3 keV, respectively) and Figure 6.10 the user-defined grid of the test example.

  
Figure 6.9: auto-grid for an acceleration energy of 2 keV

  
Figure 6.10: auto-grid for an acceleration energy of 3 keV

  
Figure 6.11: user defined grid



next up previous contents
Next: How to Use Up: How to Specify Previous: How to Specify



Horst Wagner
Tue Mar 19 10:24:55 MET 1996