&SIGNAL: SIGNAL
Signals from repeated simulations will be summed, wire by wire.
The angular spread function is integrated using the Newton-
Raphson technique with 2*n_angle+1 points.
By default, n_angle is set to 2.
In the simplified ion tail model, you have the possibility
to spread the ions that are produced in the avalanche, around
the wire.
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.
Attachment coefficients will be taken into account for signal
calculations. They occur at two instances:
- when computing the avalanche multiplication factor from the
Townsend and attachment coefficients
- when tracing the electron avalanche during the computation
of the currents induced by the electrons
Enables the avalanche setting chosen with AVALANCHE.
NOAVALANCHE leads to a fixed multiplication factor of 1.
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.
Switching on this option makes that the total induced charge
corresponds closely to the integral of the signal that is
output by the program. This is less trivial than it may sound
since signals can contain structure on a much smaller time
scale than the binning of the signal.
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.
Requests the computation of the signal induced on the sense
wires by the avalanches on different wires. Also currents
induced by electrons that do not drift to a wire will be
computed.
The option is best used in conjunction with DETAILED-ION-TAIL.
Adds an ion tail to the computed signal according to a more
detailed model in which the ions do not necessarily start at
the wire surface. Rather, they start where they are produced
during the electron avalanche.
This model is to be prefered in case the avalanche region is
substantial or when the integrated charge is important. Otherwise,
the simplified model will be faster.
Varies the arrival times of the individual electrons from the
clusters according to a Gaussian distribution.
Adds an electron pulse to the computed signal.
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.
Enables the use of the prepared track, see PREPARE-TRACK.
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.
In order to average the signal over a time bin, the
signal is interpolated with polynomials of order n_order,
and then integrated using the Newton-Raphson technique
over 2*n_average+1 points.
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 shape of the ion tail is usually stored for a series of
electron incidence angles. The reasons for this are that (a)
similar ion tails are needed for electrons from possibly many
clusters (b) the ion tail shape doesn't vary much between
nearby electron incidence angles.
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.
Separate ion tails are always kept for the different wires on
which the avalanche is produced 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]
Adds an ion tail to the computed signal according to a simplified
model in which the ions are assumed to come from the wire surface.
You may, in this model, choose the spread around the wire of the
ions that are produced in the avalanche. This can be achieved via
the ANGULAR-SPREAD keyword.
In the detailed ion tail model, the ions are traced from the point
where they were produced. This is done on a step-by-step basis of
the electron drift line that generated the ions.
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.
The fraction is initially set to 0.
Uses the Monte Carlo drifting routines rather the the default
Runge-Kutta-Fehlberg integration routines. This option is useful
if diffusion can cause electrons starting from the same starting
point to reach significantly different end points.
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 NOMONTE-CARLO-DRIFT]
Means that summing of signals over repeated simulations does not
take place.
If this option is switched on, the signal that the program
returns corresponds to the current at the point in time
indicated in the output. Any fine structure smaller than the
binning is lost.
Keyword index.
Formatted on 10/11/98.