# Slice Field Printer¶

Outputs a 2D slice of the electric, magnetic and/or current field in SI units. The slice position and the field can be specified by the user.

## .cfg file¶

The plugin works on electric, magnetic, and current fields. For the electric field, the prefix --E_slice. for all command line arguments is used. For the magnetic field, the prefix --B_slice. is used. For the current field, the prefix --J_slice. is used.

The following table will describe the setup for the electric field. The same applied to the magnetic field. Only the prefix has to be adjusted.

Command line option

Description

--E_slice.period

The periodicity of the slice print out. If set to a non-zero value, e.g. to --E_slice.period 100, the slices are generated for every 100th simulation time step.

--E_slice.fileName

Name of the output file. Setting –E_slice.fileName myName will result in output files like myName_100.dat.

--E_slice.plane

Defines the plane that the slice will be parallel to. The plane is defined by its orthogonal axis. By using 0 for the x-axis, 1 for the y-axis and 2 for the z-axis, all standard planes can be selected. E.g. choosing the x-y-plane is done by setting the orthogonal axis to the z-axis by giving the command line argument --E_slice.plane 2.

--E_slice.slicePoint

Defines the position of the slice on the orthogonal axis. E.g. when the x-y-plane was selected, the slice position in z-direction has to be set. This is done using a value between 0.0 and 1.0. E.g. by setting --E_slice.slicePoint 0.5, the slice is centered.

This plugin supports using multiple slices. By setting the command line arguments multiple times, multiple slices are printed to file. As an example, the following command line will create two slices:

picongpu # [...]
--E_slice.period 100 --E_slice.fileName slice1 --E_slice.plane 2 --E_slice.slicePoint 0.5
--E_slice.period  50 --E_slice.fileName slice2 --E_slice.plane 0 --E_slice.slicePoint 0.25


The first slice is a cut along the x-y axis. It is printed every 100th step. It cuts through the middle of the z-axis and the data is stored in files like slice1_100.dat. The second slice is a cut along the y-z axis. It is printed every 50th step. It cuts through the first quarter of the x-axis and the data is stored in files like slice2_100.dat.

### 2D fields¶

In the case of 2D fields, the plugin outputs a 1D slice. Be aware that --E_slice.plane still refers to the orthogonal axis, i.e. --E_slice.plane 1 outputs a line along the x-axis and --E_slice.plane 0 along the y-axis.

## Memory Complexity¶

### Accelerator¶

the local slice is permanently allocated in the type of the field (float3_X).

### Host¶

as on accelerator.

## Output¶

The output is stored in an ASCII file for every time step selected by .period (see How to set it up?). The 2D slice is stored as lines and rows of the ASCII file. Spaces separate rows and newlines separate lines. Each entry is of the format {1.1e-1,2.2e-2,3.3e.3} giving each value of the vector field separately e.g. {E_x,E_y,E_z}.

In order to read this data format, there is a python module in lib/python/picongpu/plugins/sliceFieldReader.py. The function readFieldSlices needs a data file (file or filename) with data from the plugin and returns the data as numpy-array of size (N_y, N_x, 3)

## Known Issues¶

See issue #348.

Should be solved with pull request #548.