20  Geometry

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The command described here is the legacy OPAL geometry interface. It should not be read as a statement that the same user-facing command set is currently mirrored in OPALX.

At present the GEOMETRY command is treated as an experimental feature. It has two roles:

  1. terminate particles that cross a boundary surface
  2. provide boundary information to geometry-aware field solvers such as SAAMG

The command supports two usage modes:

  1. import a surface mesh from an H5hut geometry file
  2. construct a predefined analytic shape: ELLIPTIC, RECTANGULAR, or BOXCORNER

20.1 Geometry Command

General form:

name: GEOMETRY, TOPO=ELLIPTIC, LENGTH=1.0, A=0.005, B=0.005;

20.1.1 Command attributes

Attribute Meaning Default
FGEOM H5hut file containing a surface mesh none
LENGTH Geometry length in meters 1.0
TOPO Analytic topology: ELLIPTIC, RECTANGULAR, BOXCORNER ELLIPTIC
S Start position of the geometry in meters 1.0
A Semi-major axis or horizontal half aperture 0.025
B Semi-minor axis or vertical half aperture 0.025
C Corner height for BOXCORNER 0.01
L1 First section length for BOXCORNER 0.5
L2 Second section length for BOXCORNER 0.2
ZSHIFT Longitudinal shift for imported H5hut geometry 0.0
XYZSCALE Uniform scaling factor for imported geometry 1.0
XSCALE Scaling factor for imported x coordinates 1.0
YSCALE Scaling factor for imported y coordinates 1.0
ZSCALE Scaling factor for imported z coordinates 1.0
INSIDEPOINT A point known to lie inside the imported geometry none

20.1.2 Analytic and file-based modes

If FGEOM is provided, the file-based surface mesh is used and the analytic TOPO selection is effectively overridden.

The analytic topologies are:

  • ELLIPTIC
  • RECTANGULAR
  • BOXCORNER

The last one is intended for piecewise box-like apertures with a corner transition controlled by C, L1, and L2.

20.1.3 Interaction with field solving and tracking

If the geometry is used only as a particle terminator, any field solver can be used and it is not necessary to attach the geometry to the FIELDSOLVER command.

If the geometry should also define field-solver boundary conditions, it must be:

  1. referenced by FIELDSOLVER
  2. selected again on RUN via BOUNDARYGEOMETRY

In all cases where particle termination is desired, the boundary geometry must be named on RUN so it is loaded and applied during tracking.