![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
![]() ![]() |
This option can for instance be used to study two-track resolution.
The ADD option can not be used after:
[By default, signals are not summed.]
Use of this keyword implies the ION-TAIL model of ion tail calculation.
[By default, n_angle is set to 2.]
The spread is to be provided as a probability distribution in terms of the angle PHI (in radians) between the incidence angle of the electron and the angle at which the ions start to drift away from the wire.
In the ION-TAIL model, ions start only from discrete angles around the wire. The number of such angles can be set with ION-ANGLES. The function that you specify is integrated around the nearest angles using Newton-Raphson integration with ANGULAR-INTEGRATION-POINTS sampling points.
The spread function may be specified as FLAT, in which case the avalanche is assumed to wrap uniformly around the wire. You may also specify NOANGULAR-SPREAD, in which case the ions will be drifted back from the nearest angular sampling point only.
Use of this keyword implies the ION-TAIL model of ion tail calculation.
Example:
Global sigma 30 signal cross ion-angles 1000 ang-spread 'exp(-((phi*180/(pi*{sigma}))**2))'
This example assumes a Gaussian angular spread with a sigma of 30 degrees. The number of discretisation points is set to 1000 in this example.
References:
Both ELECTRON-PULSE and DETAILED-ION-TAIL require Townsend coefficients. They use these coefficients, provided they are available, regardless of the setting of this option.
The averaging is done with an 2*n_average+1 point Newton- Raphson integration over a time bin centered at the point in time indicated in the output.
[By default, 5 points are used, i.e. n_average is set to 2.]
The part of the signal that is due to ionisation electrons that hit the electrode and avalanche ions that are drifting away from the electrode is called the "direct" component, the remainder of the signal is called "indirect". The two components are shown separately by e.g. PLOT-SIGNALS.
If CROSS-INDUCED is off, then Garfield computes only the direct signals. If the field is derived from a field map, the classification of signals is based on the solids. In the absence of solids, there can not be direct signals.
The option can be used in conjunction with DETAILED-ION-TAIL.
[The option is initially switch off.]
This model is to be prefered in case the avalanche region is substantial or when the integrated charge is important. This model must also be used in case the electrons hit other electrodes than wires (planes, tube, solids). Otherwise, the simpler ION-TAIL and NONSAMPLED-ION-TAIL models will be faster.
Ion tail calculation requires the possibility of drifting ions from the vicinity of electrodes. To enable this, one may have to switch CHECK-ALL-WIRES off.
[The default is ION-TAIL.]
[Diffusion is included by default, if diffusion data is present.]
The electron pulse is computed by following the avalanche process along the electron drift line, this option therefore requires the presence of Townsend coefficients. Attachment coefficients, if present, will also be taken into account. Also the INTERPOLATE-TRACK option is not compatible with ELECTRON-PULSE.
[An electron pulse is by default not included.]
This option can not be used together with ELECTRON-PULSE nor with DETAILED-ION-TAIL.
[Default: Even if a prepared track is available, it will by default not be used for the signal calculation.]
The parameter n_order should not be chosen large since especially electron pulses rise very fast. This can easily give rise to interpolated values of the wrong sign.
[A value of 1 is therefore recommended, and is also default.]
The number of electron incidence angles for which a separate ion tail is calculated can be chosen with this keyword. A value of 1 would be suitable for cylindrically symmetric detectors, while a value of order 10-50 would be appropriate if one wishes to study stereo effects.
You may specify the number of angles as NOSAMPLING (or INFINITE) to indicate that ions should start from the point where the electron hit the wire. This choice implies the use of the NONSAMPLED-ION-TAIL model. Otherwise, using this keyword implies the use of the ION-TAIL model.
Separate ion tails are kept for the different wires on which avalanches are occuring and for the different wires on which the induced current is measured. A large setting therefore implies that a large volume of data has to be stored.
[Default: 50]
You may in this model choose to spread the ions that are produced in the avalanche around the wire of. This can be achieved via the ANGULAR-SPREAD keyword.
This model, for efficiency reasons, keeps ion tails from a set of angles in memory. The number of such angles can be set with ION-ANGLES. If such sampling is not desired, then you should opt for the NONSAMPLED-ION-TAIL model, which however does not offer the possibility of spreading the avalanche around a wire.
Only electrons that hit a wire and some selected solids generate a current (direct or cross induced) in this model. DETAILED-ION-TAIL should be used if the electrons hit other electrodes such as planes, the tube and solids in general.
Ion tail calculation requires the possibility of drifting ions from the vicinity of electrodes. To enable this, one may have to switch CHECK-ALL-WIRES off.
[This is the default.]
To save CPU time, only steps are considered in which at least a certain fraction of the total number of ions is produced.
This fraction should be set to 0 for chambers filled with, for instance, liquid Helium where the avalanche develops over a large part of the electron drift line.
For conventional gaseous counters, 10**-3 to 10**-4 would be a more appropriate choice.
Using this keyword implies the use of the DETAILED-ION-TAIL model.
[The fraction is initially set to 0.]
Since all electrons from a cluster are treated independently, and since options like INTERPOLATE-TRACK can not be used in conjunction with MONTE-CARLO-DRIFT, use of this option tends to make the computations longer.
You may have to adjust the Monte Carlo parameters in the INTEGRATION-PARAMETERS statement when using this option.
[Default is RUNGE-KUTTA-DRIFT]
This option is the reverse of ADD.
[This is default.]
This model does not take the spatial extent of the avalanche into account, for which the DETAILED-ION-TAIL model should be used, nor does it provide angular spread of the ions around a wire.
Ion tail calculation requires the possibility of drifting ions from the vicinity of electrodes. To enable this, one may have to switch CHECK-ALL-WIRES off.
[The default is ION-TAIL.]
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.]
[By default, AVERAGE-SIGNAL is used with 5-point integration.]
Formatted on 0100-08-27 at 04:53.