Source file boundary.F90

The file boundary.F90 consists of the main subroutines that act as entry points to be called from other source code files and internal support routines. The external entry points are:

• Subroutines bound_e, bound_b, bound_phi, bound_j, bound_rho, bound_pe, bound_pi, bound_n:

These subroutines load the ghost cells for the electric field (bound_e), the magnetic field (bound_b), the potential phi (bound_phi), the current density (bound_j), the charge density (bound_rho), electron and ion pressure (bound_pe, bound_pi), and the density (bound_n). First the ghost cells are exchanged between neighboring processors (=subdomains) assuming that the computational domain is periodically closed in all three spatial directions (call to the internal subroutine boundary, see below). If periodic boundary conditions are applied nothing else needs to be done. For non-periodic boundary conditions the ghost cells at the domain boundary in y need to be altered appropriately according to the special type of boundary conditions. In this case either Dirichlet (f=0) or von Neumann (df/dy=0) boundary conditions are supported.
For the full-particle version three types of boundary conditions are available:
1. periodic in all three directions
2. 2-D GEM boundary conditions: These boundary conditions can be translated to a larger periodic system. For this purpose the original domain [0...L_x, 0...L_y] is doubled by rotating the real domain around the x axis and attaching it as a virtual domain at [0...L_x,L_y...2*L_y]. Thus, scalar data at the coordinates (x,y) and (x,2*L_y-y) are identical whereas the sign of vector quantities changes accordingly.
3. 3-D GEM boundary conditions: or the 3-D case a conducting wall is introduced at y=0 and y=L_y.
For the hybrid and the two-fluid version only periodic boundary conditions are available at present. In case other boundary conditions are implemented the source files hybrid.M and twofluid.M need to be checked carefully, if the calls to the bound_... routines always lead to the expected boundary conditions. This is of particular importance for the potential phi, i.e. the solution to the Helmholtz equation and the artificial viscosities.
• Subroutines virtual_charge, virtual_current:

For non-periodic boundary conditions virtual particles beyond the boundary of the domain may be necessary (compare subroutines calc_rho and calc_j in source file particles.F90). If for example a conducting wall is located at y=0 each particle at position (x,y) corresponds to a virtual particle at (x,-y). The subroutine virtual_charge determines the sign of the virtual charge: The virtual charge is given by the charge of the real particle multiplied by the value returned by the subroutine. Analogously the components of the virtual current are controlled by the subroutine virtual_current. The two subroutines are called by calc_rho and calc_j in the source file particles.F90.
• Function non_periodic:

The function non_periodic returns the values .true. or .false. depending on whether the boundary conditions are periodic or not. It is called by subroutines in the source file particles.F90. In bound_rho_j it is used to determine whether charge/current that was collected in the ghost cells at the domain boundary in y is to be transferred periodically. In subroutine stepx the result of function non_periodic is used to decide how particles are treated that leave the domain in y: Should they be periodically transferred or should they be reflected?
• Subroutine bound_particle:

The subroutine bound_particle specifies which velocity components of a particle that hits the boundary should be inverted (in case there is a wall).
• Subroutines smooth_e, smooth_j, smooth_rho:

These subroutines are called to average the current density, the charge and the electric field that acts on the particles over the closets grid cells to reduce the noise level.

• Subroutine boundary:

The subroutine boundary loads the ghost cell layers by exchanging data between adjacent processors. It contains the calls to the MPI routines which perform the communication.
• Subroutines dirichlet, von_neumann:

These two subroutines alter the ghost cells along the domain boundary in y such the Dirichlet or von Neumann boundary conditions are satisfied.
• Subroutine smooth:

This routine performs the smoothing of the electric field, the current and the charge density after the boundary conditions have been set appropriately by the calling routine.

• boundary_condition:

This switch determines which type of boundary conditions is used. Possible values are
1. #define boundary_condition periodic
2. #define boundary_condition gem_reconnection (full particle version only)
3. #define boundary_condition gem_3d (full particle version only)
Make sure that the initial data set used for start-up satisfies the chosen boundary conditions.