4.12 translate

• description: Sets up repeated translation of the memory used for the mesh in the +z direction to follow the beam. This can be used to simulate a long drift while using less computing time and less memory. There has been little testing of this feature!
• example:
  &translate  
          z_trigger = 0.05,  
          z_lower = 0.02,  
          z_upper = 0.055  
  &end

  This specifies that when the first particle passes z = 5cm, the mesh will be contracted to cover the region from z = 2cm to z = 5.5cm. Thereafter, each time a particle advances by one longitudinal mesh spacing, the grid will be translated that same distance in the +z direction.

  The boundary conditions are changed to Neumann on the upper, right, and left boundaries and Dirichlet on the lower boundary.

• synopsis and defaults:
  &translate  
          z_lower = <zMin>,  
          z_upper = <zMax>,  
          z_trigger = <z0>,  
  &end

  where <zMin> and <zMax> are the minimum and maximum longitudinal coordinates for the original problem mesh, and <z0> is <zMax>-5 * Δz, where Δz is the mesh spacing.

• details:
  • z_trigger: The first time any particle passes the longitudinal position given for this variable, mesh reduction is triggered and translation is enabled. Prior to this time, the translate command has no effect. After this time, translation by Δz occurs every time the maximum longitudinal particle position increases by Δz.
  • z_lower: The lower limit of the longitudinal extent of the reduced mesh.
  • z_upper: The upper limit of the longitudinal extent of the reduced mesh.