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&DRIFT: DRIFT


EDGES

Indicates that the drift line calculation will begin at some of the boundaries of the drift area as set by AREA.

You can select the edges from which drift lines should start and you can also set the number of drift lines from each edge with the LINES keyword.

An example of an EDGES drift line plot, made with the following command:

drift edge left right notup notdown isochrone 0.02

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SOLIDS

Requests that the electrons or ions start to drift from the intersection between the SELECTed solids and the viewing plane.

You can control the number of drift lines from each solid with the LINES keyword.

ELECTRONs are usually not produced near the electrodes and they are therefore drifted by default 'in reverse', i.e. with a positive charge. The resulting plot shows the origin of all electrons that can end up on the electrode.

Since IONs are normally produced near the electrode surface, they are drifted in their usual mode, i.e. with a positive charge. The resulting plot therefore shows where ions go that are produced in an avalanche at the electrode.

To modify this behaviour, i.e. to study electrons drifting away from electrodes that repel electrons and ions drifting away from electrodes that attract ions, use the POSITIVE and NEGATIVE options.

A SOLIDS drift line plot made with a finite element field map of the read-out structure of a TPC.

drift solid lines 50 ion positive contour 10 l-pl nol-pr
Solids have been defined to represent the octagonal cathode, the gating structure (top of the figure) and the avalanche wire, at the origin. The drift lines start from the wire. The plot has been made with the default isochrone settings.

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WIRES

Requests that the electrons or ions start to drift from the surfaces of the wires that have been SELECTed.

You can control the number of drift lines from each wire with the LINES keyword.

ELECTRONs are usually not produced near the wires and they are therefore drifted by default 'in reverse', i.e. with a positive charge. The resulting plot shows the origin of all electrons that can end up on the wire.

Since IONs are normally produced near the wire surface, they are drifted in their usual mode, i.e. with a positive charge. The resulting plot therefore shows where ions go that are produced in an avalanche at the wire.

To modify this behaviour, i.e. to study electrons drifting away from wires that repel electrons and ions drifting away from wires that attract ions, use the POSITIVE and NEGATIVE options.

An example of a WIRES drift line plot, made with the following command:

int-par iso-connect 0.1
drift wire lines 30 isochrone 0.02
The distance over which isochrone segments are connected has been limited in this example for clarity, See ISOCHRONE-CONNECTION-THRESHOLD for more information on this.

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TRACK

Indicates that the drift line calculation will begin on the track.

The resulting plot depends to a large extent on the clustering model you have selected with the TRACK command:

Unlike drifting from solids, edges or wires, DRIFT TRACK does not take its number of lines from a LINES keyword.

Although permitted, the ION option is not meaningful used together with the latter two clustering models.

An example of a TRACK drift line plot, made with the following command:

track -2.9 0.9 2.9 0.9 muon energy 1 GeV
drift track noisochrone
This figure shows a Heed simulation of a 1 GeV muon in Argon-ethane, see HEED for more information on this.

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ZERO

Indicates that the drift line are calculated from the zeroes of the electrostatic field, both in the attracting and in the repelling directions.

The ELECTRON/ION and POSITIVE/NEGATIVE settings are ignored. This choice is useful when you're determining the precise acceptance boundaries for each of the wires.

Note: zero finding is not available yet in the default version of Garfield.


RUNGE-KUTTA-DRIFT

Requests the use of the Runge_Kutta_Fehlberg algorithm for computing drift lines.

Runge Kutta integration is easier to use than Monte Carlo stepping in that the integration parameters are more tolerant.

The parameters controling the accuracy are adjusted for chambers that are several centimeters large. When studying much smaller structures, at the micron scale, one may wish to request more accuracy.

The Runge Kutta algorithm is well suited for smooth fields, such as those obtained with analytic potentials. The field computed from field maps is sometimes not even continuous, and one should in such cases prefer the Monte Carlo algorithm.

[The initial default is RUNGE-KUTTA-DRIFT.]


MONTE-CARLO-DRIFT

Requests Monte_Carlo calculation of a drift path, instead of a Runge Kutta Fehlberg integration.

This option is particularly interesting used in conjuction with drifting from a TRACK and on which clusters are generated with HEED.

When using this option, care has to be taken that the step_size has been set to a value appropriate to the chamber.

[The initial default is RUNGE-KUTTA-DRIFT.]


ISOCHRONES

Requests calculation and plotting of isochrones. You must specify the interval, in microsec, after the ISOCHRONES keyword.

The appearance of the isochrones is affected by:

Plotting isochrones can be a CPU intensive operation, depending on the number of drift lines, the number of isochrones and the options that have been chosen.

In order to plot only the isochrones and not the drift lines, one uses ISOCHRONES in conjunction with NOLINE-PLOT.

The drift time used for the isochrones is measured from the wire or the solid where the electron or ion ends up. Isochrones are only plotted for electrons and ions that do reach a wire or a solid. Isochrones are not plotted for particles that reach a replica of a wire (in case of periodic chambers).

Note that isochrones can also be obtained with TABLE CONTOUR and with PLOT-FIELD CONTOUR TIME. These commands do not take the end-point of the electrons into account, and as a result may produce isochrones joining points leading to different wires or solids.

[Isochrones are by default not plotted.]


LINE-PLOT

Requests plotting of the drift lines. You may wish to switch this option off if you want to see only isochrones.

Electron drift lines are plotted with the representation E-DRIFT-LINE and ion drift lines with ION-DRIFT-LINE.

[This option is initially on.]


LINE-PRINT

Requests printing of drift line summary data.

This option is not compatible with LINE-PLOT in interactive VM/CMS (because of system shortcomings) unless the output has been rerouted (> dsname).

This option is initially off.


ELECTRON

Requests drifting of electrons.

ION

Requests drifting of ions.

POSITIVE

By default, electrons are drifted with negative charge and ions with positive charge. If you wish to see the origin of the electrons and ions arriving at a given position, you may wish to reverse the sign.

The POSITIVE option forces the charge to be positive, no matter whether the particle is an electron or an ion.

[The default setting of this option depends on the context.]


NEGATIVE

By default, electrons are drifted with negative charge and ions with positive charge. If you wish to see the origin of the electrons and ions arriving at a given position, you may wish to reverse the sign.

The NEGATIVE option forces the charge to be negative, no matter whether the particle is an electron or an ion.

[The default setting of this option depends on the context.]


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Formatted on 0103-05-16 at 14:05.