Simulation window and grids

Fields and densities grid

The grid on which the fields and densities are calculated.

Fields and densities (\(ro\), \(j\)) are calculated on a config.grid_steps x config.grid_steps-sized grid. This number must be odd in order to have an on-axis cell for on-axis diagnostics.

config_example.grid_steps = 641

Transverse grid size in cells

config_example.grid_step_size = 0.025

Transverse grid step size in plasma units

The fields are calculated at the centers of the grid cells.

Note

The muddy concept of ‘window width’ is no longer referenced in LCODE 3D to ease up the inevitable confusion about what it actually means and how it relates to config.grid_step_size. Please refrain from thinking in these terms and head over to the following subsection for more useful ones.

Reflect and ‘plasma’ boundaries

The reflect and plasma boundaries illustrated.

config_example.reflect_padding_steps = 5

Plasma reflection <-> field calculation boundaries

config_example.plasma_padding_steps = 10

Plasma placement <-> field calculation boundaries

The plasma partlcles are not allowed to enter the outermost cells in order to simplify the treatment of boundary regions during interpolation, deposition and field calculation [Zero special boundary treatment]. In order to achieve that, the reflection boundary is placed config.reflection_padding_steps steps deeper into the simulation area.

Note

While choosing the value for this parameter, one should take into account the particle size. Even a single fine [Coarse/fine plasma] particle is three cells wide in deposition, [Plasma], so the gap width should be wide enough to cover the entire coarse particle cloud size. Failure to meet this condition may result in a memory violation error. This could be solved by introducing fine particle reflection, but that’d be more resource-intensive.

Note that while it defines the area where plasma is allowed to be present, it must be larger than the area where the plasma is initially positioned. The size of the second area is controlled by the config.plasma_padding_steps, which puts a cut-off limit on the placement of both coarse and fine plasma particles.

Coarse and fine plasma grids

Finally, the plasma boundary hosts two grids of particles, the coarse grid and the fine grid [more info in Coarse/fine plasma approach], which are coarser and finer than the field grid respectively.