&CELL: FIELD-MAP

FILES

The set of files to be read in. The files can contain the mesh or maps of:

the potential,
the electric E-field,
the electric D-field,
one or more weighting fields,
the magnetic field,
the dielectric constant.

Notes:

All maps, weighting fields included, must share the same grid.
The weighting field of an electrode is the electric field that results from setting the potential of that electrode to 1 and all others to 0. (Strictly speaking, the potential should be 1, and not 1\ V.) This field is used to compute the signals induced on an electrode by moving charges.
The D field is only used to compute the dielectric constants by comparison with E.
Should you, under duress, have to use Windows to prepare the field maps, then take care to remove spurious end-of-line sequences, such as control-M, from the field maps.

Additional information on:

contents	file
label	format

DRIFT-MEDIUM

If you provide a map of the dielectric constants, of the conductivity, or both a map of D and a map of E, you have the possibility to specify which of the materials is the drift medium.

There are 3 ways to select the drift medium:

via an integer: this is interpreted as a sequence number in the sorted list (from small to large) of dielectric constants or the conductivities;
via a real: this is interpreted as a dielectric constant divided by \ε\<SUB\>0\</SUB\> (i.e. a gas typically has a value close to 1), or a conductivity (a gas usually does not conduct and has a conductivity close to 0); the list of material constants present in the field map is searched for the nearest match;
via a keyword such as SMALLEST.

Beware: DRIFT-MEDIUM\ 3 is not the same as DRIFT-MEDIUM\ 3.0\ ! In the first case, the medium with the 3rd dielectric constant or the 3rd conductivity will be selected. In the second case, the medium with the dielectric constant or the conductivity closest to 3 will be taken.

When using the DC conduction mode, it may be more natural to use the keywords SMALLEST-SIGMA, SECOND-SMALLEST-SIGMA, SECOND-LARGEST-SIGMA and LARGEST-SIGMA which are treated as synonyms of the keywords listed in the command description.

[By default, the medium with the lowest dielectric constant or the lowest conductivity is assumed to be the drift medium.]

RESET

Resets the field map, has the same effect as RESET FIELD-MAP.

NOT-X-PERIODIC

Specifically states that the field map is not periodic in x.

[This is the default.]

X-PERIODIC

States that the field map has an x-periodicity.

The length of one period is taken to be the maximum extent in x of the field map.

A cell can not be both X-PERIODIC and X-MIRROR-PERIODIC, but can be X-AXIALLY-PERIODIC in addition to being translation periodic in the x-direction.

[By default, a field map is not assumed to be periodic.]

X-MIRROR-PERIODIC

States that only half of the cell has been entered and that there is a mirror image on both sides. In addition, the cell has a periodicity, equal to twice the maximum extent in x of the field map.

A cell can not be both X-PERIODIC and X-MIRROR-PERIODIC, but can be X-AXIALLY-PERIODIC in addition to being translation periodic in the x-direction.

[By default, a field map is not assumed to be periodic.]

X-AXIALLY-PERIODIC

States that the cell has an axial periodicity around the x-axis and that only one period is represented in the field map.

The length of one period is deduced from the field map, and is therefore not specified on the FIELD-MAP statement.

The symmetry axis must pass through y=z=0.

A cell can not be both X-PERIODIC and X-MIRROR-PERIODIC, but can be X-AXIALLY-PERIODIC in addition to being translation periodic in the x-direction.

[By default, a field map is not assumed to be periodic.]

X-ROTATIONALLY-SYMMETRIC

Specifies a rotational symmetry.

The field map has to be 2-dimensional. Elements must be used that are suitable for rotational symmetry. Currently, all interfaced finite element programs use the second field map coordinate axis, which we refer to as height, h, as axis of rotational symmetry. We call the first coordinate axis the radius, r. The field map must not contain any element or part of element at r\ \<\ 0.

The way the finite element program is informed about the rotational symmetry varies with the programs - consult the documentation.

The above is common for all 3 rotational symmetries. The difference is in the way the (r,h) field-map coordinates are computed from the chamber (x,y,z) coordinates. When using X-ROTATIONALLY-SYMMETRIC, the assignment is:

r = \&radic;(y\&sup2; + z\&sup2;)
h = x

A chamber can have only one rotational symmetry at the time.

[By default, a field map is not assumed to be periodic.]

NOT-Y-PERIODIC

Specifically states that the field map is not periodic in y.

[This is the default.]

Y-PERIODIC

States that the field map has an y-periodicity.

The length of one period is taken to be the maximum extent in y of the field map.

A cell can not be both Y-PERIODIC and Y-MIRROR-PERIODIC, but can be Y-AXIALLY-PERIODIC in addition to being translation periodic in the y-direction.

[By default, a field map is not assumed to be periodic.]

Y-MIRROR-PERIODIC

States that only half of the cell has been entered and that there is a mirror image on both sides. In addition, the cell has a periodicity, equal to twice the maximum extent in y of the field map.

A cell can not be both Y-PERIODIC and Y-MIRROR-PERIODIC, but can be Y-AXIALLY-PERIODIC in addition to being translation periodic in the y-direction.

[By default, a field map is not assumed to be periodic.]

Y-AXIALLY-PERIODIC

States that the cell has an axial periodicity around the y-axis and that only one period is represented in the field map.

The length of one period is deduced from the field map, and is therefore not specified on the FIELD-MAP statement.

The symmetry axis must pass through x=z=0.

A cell can not be both Y-PERIODIC and Y-MIRROR-PERIODIC, but can be Y-AXIALLY-PERIODIC in addition to being translation periodic in the y-direction.

[By default, a field map is not assumed to be periodic.]

Y-ROTATIONALLY-SYMMETRIC

Specifies a rotational symmetry.

The way the finite element program is informed about the rotational symmetry varies with the programs - consult the documentation.

The above is common for all 3 rotational symmetries. The difference is in the way the (r,h) field-map coordinates are computed from the chamber (x,y,z) coordinates. When using Y-ROTATIONALLY-SYMMETRIC, the assignment is:

r = \&radic;(x\&sup2; + z\&sup2;)
h = y

A chamber can have only one rotational symmetry at the time.

[By default, a field map is not assumed to be periodic.]

NOT-Z-PERIODIC

Specifically states that the field map is not periodic in z.

[This is the default.]

Z-PERIODIC

States that the field map has a z-periodicity.

The length of one period is taken to be the maximum extent in z of the field map.

A cell can not be both Z-PERIODIC and Z-MIRROR-PERIODIC, but can be Z-AXIALLY-PERIODIC in addition to being translation periodic in the z-direction.

[By default, a field map is not assumed to be periodic.]

Z-MIRROR-PERIODIC

States that only half of the cell has been entered and that there is a mirror image on both sides. In addition, the cell has a periodicity, equal to twice the maximum extent in z of the field map.

A cell can not be both Z-PERIODIC and Z-MIRROR-PERIODIC, but can be Z-AXIALLY-PERIODIC in addition to being translation periodic in the z-direction.

[By default, a field map is not assumed to be periodic.]

Z-AXIALLY-PERIODIC

States that the cell has an axial periodicity around the z-axis and that only one period is represented in the field map.

The length of one period is deduced from the field map, and is therefore not specified on the FIELD-MAP statement.

The symmetry axis must pass through x=y=0.

A cell can not be both Z-PERIODIC and Z-MIRROR-PERIODIC, but can be Z-AXIALLY-PERIODIC in addition to being translation periodic in the z-direction.

[By default, a field map is not assumed to be periodic.]

Z-ROTATIONALLY-SYMMETRIC

Specifies a rotational symmetry.

The way the finite element program is informed about the rotational symmetry varies with the programs - consult the documentation.

The above is common for all 3 rotational symmetries. The difference is in the way the (r,h) field-map coordinates are computed from the chamber (x,y,z) coordinates. When using Z-ROTATIONALLY-SYMMETRIC, the assignment is:

r = \&radic;(x\&sup2; + y\&sup2;)
h = z

A chamber can have only one rotational symmetry at the time.

[By default, a field map is not assumed to be periodic.]

LINEAR

Requests linear interpolation of all fields within each triangle or each tetrahedron. This leads to interpolated fields that are continuous, but have a discontinuous first derivatives at the boundaries between the triangles/tetrahedrons.

This method can be applied to all field maps.

[By default, the highest order method permitted by the field map will be used.]

QUADRATIC

Requests quadratic interpolation of the fields within each triangle or each tetrahedron. The interpolation is done using normalised Lagrange polynomials in terms of the triangular coordinates. This ensures that the field on triangle/tetrahedron boundaries depends only on the field values of the nodes located on the boundary. Therefore, the interpolated fields are continuous, but the first derivative is in general not continuous across boundaries between adjacent triangles/tetrahedrons.

This method can only be applied to field maps with additional nodes halfway the vertices. This information is present in for instance all Maxwell field maps.

[By default, the highest order method permitted by the field map will be used.]

CUBIC

Requests cubic interpolation of the fields within each triangle or each tetrahedron. The interpolation is done using normalised Lagrange polynomials in terms of the triangular coordinates. This ensures that the field on triangle/tetrahedron boundaries depends only on the field values of the nodes located on the boundary. Therefore, the interpolated fields are continuous, but the first derivative is in general not continuous across boundaries between adjacent triangles/tetrahedrons.

This method can only be applied to field maps with additional nodes at 1 third and at 2 thirds between the vertices. There are currently no field map formats with which this interpolation order can be used.

[By default, the highest order method permitted by the field map will be used.]

INTERPOLATE-ELECTRIC-FIELD

Requests the calculation of the electric field by interpolating in the electric field tables as provided by the finite element program.

This interpolation is meaningful only if the finite element program outputs, for a single node, as many electric field vectors as there are elements to which the node belongs. The reason for this is that, contrary to the potential, the electric field is as a rule discontinuous across element boundaries. This discontinuity exists even if \ε is the same on both sides. Many finite element programs output only one electric field vector per node. When using these, COMPUTE-ELECTRIC-FIELD should be selected.

This option is currently only active for hexahedral field maps. It is automatically set for several field map formats, such as those produced by Ansoft programs..

[This option is default.]

COMPUTE-ELECTRIC-FIELD

Requests the calculation of the electric field using the potentials at the nodes. This technique works by taking the derivatives of the shape functions to the natural coordinates, multiplied by the Jacobian of the transformation of the natural coordinates to user coordinates.

For elements with use isoparametric coordinates, which is nearly always the case, this calculation entails little or no overhead since the Jacobian is reused from the iterative calculation of the local coordinates.

These derivatives are reliable also in case the nodes happen to lie on an interface between materials of different \εs.

This option is automatically switched on when using ANSYS-solid-123, ANSYS-plane-121 and several other finite element programs.

[This option is not default.]

DELETE-BACKGROUND

Removes the background from the field map. Background elements are usually pieces of conductors, in which there is no field.

Option active with Maxwell Field Simulator 3D and ANSYS:

Maxwell: This option relies on the .shd project file. This file is produced by Maxwell as part of its regular output. In newer versions, it is sometimes written to a different directory from the mesh files. Garfield only looks for this file in the directory of the mesh files and you may therefore have to copy the file.
ANSYS: Elements are eliminated if the resistivity of the material is strictly equal to 0. The resistivity is obtained from an MPLIST file stored in the same directory as the field map. No elements are deleted if no such file is found. Temperature-dependent resistivities are not processed.

Note: this option is implicit with the MAXWELL-11 format.

[This option is on by default.]

Z-RANGE

Every cell needs, for Garfield, to have a default extent in all 3\ dimensions. When the cell contains only wires and planes, then the extent in z is derived from the length of the wires. When instead, a 2-dimensional field map is used, there is no way to know the z-extent of the cell.

This argument is ignored if the field map is 3-dimensional.

[By default, the cell is assumed to go from -50\ cm to +50\ cm in the z-direction.]

OFFSET

Requests the field map be shifted.

By default, Garfield uses the coordinate system from the finite element program. As a rule, this doesn't lead to limitations.

However, in case overlays an analytic field with a finite element field, it may happen that the fields need to be aligned. Such an alignment can be obtained with the OFFSET option.

If you specify an offset of (xoff,yoff,zoff), then Garfield will interpolate the field map at (x-xoff,y-yoff,z-zoff) when it needs a field at (x,y,z).

All 3\ coordinates should be specified, even if the field map is 2-dimensional.

[By default, the 3 offsets are set to 0. The offsets are saved with the binary field maps.]

UNIT

The distance unit used in the field map. The unit must be one of the following:

MICROMETRE or MICRON or MUM
MILLIMETRE or MM
CENTIMETRE or CM
METRE or M

This information is only used for COMSOL-2d-linear, COMSOL-2d-quadratic, COMSOL-3d-linear, COMSOL-3d-quadratic, ANSYS-solid-123 and ANSYS-plane-121 field maps.

[By default, the centimetre is assumed as length unit.]

PLOT-MAP

Requests the materials to be shown in plots of the chamber.

Materials are distinguished by their dielectric constant or their conductivity. A map of either of these must therefore be available for this option to have effect. Maps of the dielectric constant an the conductivity can be supplied as such. A map of the dielectric constant will automatically be computed also if maps of both E and B are present.

The material with the smallest dielectric constant is shown with representation MATERIAL-1. The medium with the next highest dielectric constant with MATERIAL-2 etc. The drift medium is never shown.

Elements of a 2D field map are only shown in X-Y views and in CUT views at a constant z. The cross sections of the viewing plane with the elements of a 3D field map are shown in X-Y, X-Z, Y-Z and CUT views, but not in 3D views.

Field maps do not usually cover areas filled with conducting material since there is no field inside. To visualise these, one has to enter them manually with the SOLIDS command. SOLIDS doesn't interfere with PLOT-MAP.

This option can also be switched on and off with the PLOT-MAP option of the AREA command.

[By default, the map is shown.]

HISTOGRAM-MAP

Requests histograms to be plotted of the aspect ratio (i.e. the ratio of the largest and the smallest vertex separation) and of the surface or volume of the elements in the mesh.

Elements with large aspect ratios can be a sign that the mesh is of poor quality. One should then consider using the so-called virtual-volumes technique to constrain the mesh elements.

Elements with a very large volume or surface are likely to cause problems when transporting particles since the finite element method only guarantees continuity of the potential, not of the electric field. With large elements, the discontinuity across element boundaries is likely to be large.

Switching on this option further enables checks on the elements to be carried out, in particular a search for irregular element degeneracy.

[These histograms are not made by default.]

Go to the top level, to &CELL, to FIELD-MAP, to the topic index, to the table of contents, or to the full text.

Formatted on 21/01/18 at 16:55.