Vortex simulation

How to create a simple vortex on POV Ray, using the instruction union and difference.
// POV-Ray 3.7 Scene File "Prova4.pov"
// author:  Max
// Date:   01/03/2015
//--------------------------------------------------------------------------
#if (version < 3.7) global_settings{ assumed_gamma 1.0 } #end
//--------------------------------------------------------------------------
#include "colors.inc"
#include "textures.inc"
//--------------------------------------------------------------------------
// camera ------------------------------------------------------------------
#declare Camera_0 = camera {ultra_wide_angle angle 65          // vista frontale
                            location  <0.0 , 3.0 ,-3.5>
                            right     x*image_width/image_height
                            look_at   <0.0 ,-0.5 , 0.0>}
camera{Camera_0}

// sole ---------------------------------------------------------------------
light_source{<1500,3000,-3000> color White}
// cielo ---------------------------------------------------------------------
plane{<0,1,0>,1 hollow no_shadow
       texture{ pigment{ Bright_Blue_Sky scale 1
                        }
                finish {ambient 1 diffuse 0} }     
       scale 10000}
// nebbia ---------------------------------------------------------------------

fog{fog_type   2
    distance   20
    color      rgb<1,0.98,0.9>
    fog_offset 0.1
    fog_alt   1
    turbulence 0.8}
 
   
// terreno ------------------------------------------------------------------
// dimensioni del foro:
#declare ForointernoR = 1.00;
#declare Foroscala  = 1.25;
#declare ForoR      = 0.75;

//-------------------------
// piano forato:
union{
difference{

plane{<0,1,0>, 0 }
cylinder{<0,-ForoR,0>, <0,0.001,0>,ForointernoR+ForoR scale Foroscala}
cylinder{<0,  -100,0>, <0,0.001,0>,ForointernoR scale Foroscala}
          } // fine della differenza
         
torus{ ForointernoR+ForoR, ForoR
       translate<0,-ForoR,0>scale Foroscala}

 texture{Polished_Chrome 
         normal {spiral1  20  0.25  sine_wave   
                 turbulence 0.1 rotate<90,0,0> scale <0.25,0.5,0.25> }
         finish {ambient 0.15 diffuse 0.85 reflection 0.35}}
 } // fine dell'unione 

 //sfera sospesa
 sphere { <0,-ForoR,0>, ForoR/3

        texture { pigment{ color rgb<0.75, 0.75, 0.75>}
                  finish { phong 1.0 reflection 0.01}
                }

          scale<1,1,1>  rotate<0,0,0>  translate<0,0.5,0> 
       }  // fine della sfera -----------------------------------

//-----------------------------------------------------------------------fine
Here the picture obtained from the program written above.