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&CELL: FIELD-MAP


FILES

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

Notes:

  1. All maps must share the same grid.
  2. The weighting field of an electrode is the electric field that results from placing that electrode at 1 V and earthing all others. This field is used to compute the signals induced on an electrode by moving charges.
  3. The D field is only used to compute the dielectric constants by comparison with E.

contents

One may specify the contents of the file before the name. This is mandatory in the following cases:

In case Maxwell Field Simulator has been used to generate the maps, identifying the mesh directory is recommended. The contents is optional for all other types of data written by Maxwell programs.

A warning is issued if the file contains other data than the declared contents.

Currently, the following contents types are recognised:

Name Used to compute
B-FIELD (=MAGNETIC-FIELD) Drift lines
ELECTRIC-FIELD Drift lines, various other plots
D-FIELD Epsilon by comparing E and D
MATERIAL (=D-FIELD) Drift line termination
MESH Always needed with Maxwell Field Simulator
POTENTIAL (=VOLTAGE) Contour maps
WEIGHTING-FIELD Induced signals


label

Serves two purposes:
  1. The label links a weighting field with solids. For this association, the weighting field label should match one or more labels used in the SOLIDS listing. A solid label should not match more than one weighting field label, unless the signals for these weighting fields are summed. In the absence of a match, all signals on the weighting field map are classified as cross induced. Such signals are only computed if the CROSS-INDUCED option is active.
  2. The label identifies the weighting field to the SELECT statement, a prerequisite for the computation of signals in the electrodes for which the weighting field has been computed.

The label is a single character.

No label should be assigned to other fields than the weighting fields.

[By default, the label "S" is assigned to weighting field maps, which makes these maps are part of the initial, default, selection.]


format

Specifies the program that has been used to generate the field maps. Currently, the following formats are accepted:

With the exception of Tosca, all formats are automatically recognised, and a format doesn't have to be specified therefore.

Recipes for creating field maps with these programs are given in the sub-topics.

Additional information on:
  
 


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:

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.]


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.]


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.]


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.]


DELETE-BACKGROUND

Option only active with Maxwell Field Simulator 3D.

Removes the excluded parts of the background from the field map.

[This option is on by default.]


WINDOW

The WINDOW keyword is used to eliminate triangles or tetrahedrons from the mesh.

A triangle or a tetrahedron is eliminated whenever one of its vertices is located outside the window.


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.]


PLOT-MAP

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

The option has effect only if material properties have been entered, either as a map of dielectric constants or as maps of both D and E.

The materials are distinguished by their dielectric constant, which must therefore have been entered with the FIELD-MAP command. This can be done with an explicit map of dielectric constants, but also by a comparison of maps of E and D.

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 these. 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 within a tetrahedron or triangle) and of the surface or volume of the tetrahedrons or triangles in the mesh that is read.

Tetrahedrons and triangles with large aspect ratios can be a sign that the mesh is of poor quality. When using Maxwell, one should consider adding dummy volumes which constrain the mesh elements (contact CERN Maxwell support or Ansoft for further information).

Tetrahedrons with a very large volume and triangles with a very large surface are likely to cause problems while drifting particles since the E field inside is linear, without guaranteed match with neighbouring elements.

[These histograms are not made by default.]


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Formatted on 0099-12-08 at 15:52.