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&DRIFT: ARRIVAL-TIME-DISTRIBUTION

plane

This command works in either the x-y, the y-z or the z-x plane, optionally with a constant OFFSET in the 3rd direction.

In all 3 cases, one of the 2 axes of the plane, the one that we call here "stepping axis" serves as coordinate in the calibration curve. The tracks cross a line through the centre of the electrode being studied and parallel to the stepping axis at multiples of a user-defined INCREMENT.

The axis which should serve as stepping axis is identified with the STEP keyword. You can set the RANGE of coordinates along the stepping axis for which tracks should be generated.

The other axis in the plane is called "scanning axis". The tracks can be at an ANGLE to this axis, but will usually be parallel to it.

The axis which should serve as stepping axis is identified with the SCAN keyword. Like for the stepping axis, You can limit the RANGE of coordinates along the stepping axis.

electron

The electrons on which you trigger. These are usually small numbers, around 5, but you are free to choose larger values. You may list several electrons, up to a compilation dependent limit (currently set to 10).

In the rest of the descriptions, these electrons are referred to as the 'selected electrons'.

If a value is negative, then the electrons will be counted from the back, the last electron corresponds to a value of 0. For the 4 last electrons, you can also type LAST, ONE-BUT-LAST, TWO-BUT-LAST and THREE-BUT-LAST.

[Default: initially, only the 25th electron is selected. The set of selected is remembered as default for the next call.]

threshold

A probability between 0 and 1 (both excluded). Apart from the mean arrival time of the selected electron, Garfield outputs also the time at which the selected electron has a given probability to have arrived.

[Default: initially 0.5, the median of the distribution. The value set is kept as default for the next call.]

TIME-WINDOW

Whilst the program can compute reasonable bounds for the overall arrival time distribution histogram, it can not do so for the histogram of the selected electron.

You have, for these histograms, the choice between:

If you specify an explicit time window, then this time window is also used for the all-electrons arrival time histogram. Otherwise, these histograms are booked with the full time range of the track.

Setting a time window is most useful in conjunction with the KEEP-HISTOGRAMS option when you wish to study the histograms in more detail by other programs.

[Default: by default the time range of the selected electron histogram is computed from the first 100 entries of this histogram, whereas the range of the all-electron histogram is set to the time range for the track under study.]

Additional information on:

STEP

Determines, together with SCAN, the plane in which the tracks will be located.

Tracks are usually perpendicular to the stepping axis and at regularly spaced distances from the centre of the electrode. The distance between 2 successive tracks, measured along the stepping axis, can be set with INCREMENT. The part of the stepping axis for which tracks are to be generated can be set with RANGE.

The stepping axis must be either the x-, the y- or the z-axis and must be distinct from the scanning axis.

[By default: X]

Additional information on:

SCAN

Determines, together with STEP, the plane in which the tracks will be located.

Tracks are usually parallel to the scanning axis, or at a small ANGLE to it.

The scanning axis must be either the x-, the y- or the z-axis and must be distinct from the stepping axis.

[By default: Y]

Additional information on:

OFFSET

By default, this command works in a plane that contains the origin.

If you wish to compute arrival time distributions in a parallel plane, then specify OFFSET followed by the 3rd coordinate of the plane.

DIFFUSION

By default, diffusion is included in the arrival time calculations. If you wish to study the impact diffusion has on the distributions, then it may be convenient to be able to switch diffusion off. This can be achieved by selecting the NODIFFUSION option.

ATTACHMENT

Depending on the presence of attachment data or not, attachment is or is not included. If attachment data is present, but if you do not want the effect to be taken into account, then you can specify NOATTACHMENT.

LINES

Each track is first 'prepared': from regularly spaced points on the track, electrons are drifted and the drift times and integrated diffusion coefficients are stored for interpolation when doing the Monte-Carlo cycles. Where the drift time changes most between 2 points, additional drift-lines are calculated.

The parameter lines is the total amount of drift-lines that are calculated this way: 75\ % in the first step and 25\ % in the second.

[Default: the LINES parameter from the drift section.]

bins

The number of bins in the histograms used to compute the time at which the selected histogram has a given probability to have arrived - the mean arrival time is computed directly without histogram.

[Default: initially half of MXLIST, usually 100-500 bins. The value that you set is kept as default for the next call.]

KEEP-HISTOGRAMS

This option can be used to store the arrival time histograms for later study. The histograms are made accessible via global variable names that are displayed while the command is carried out (SEL_n, and ALL_n with n a counter).

A common application of this option seems to be the Gaussian fit of the arrival time histograms. This can be done using the FIT_GAUSSIAN procedure, or by a user program after writing the histograms out with the WRITE_HISTOGRAM procedure.

You have to declare the Global variables before the loop if

Declaring is not required if the variables are only used outside the loop, in procedure Calls, in Say statements or for substitution in normal input statements.

[Default: histograms are not kept. The setting is kept across calls of ARRIVAL.]

KEEP-RESULTS

If this option is selected, then the x(t) relations that have been obtained by ARRIVAL, will be stored as a set of matrices and numbers:

Global Description Type
[X|Y|Z]_<electrode> Distance from electrode Matrix
MEAN_<electrode> mean time all electrons Matrix
MEDIAN_<electrode> median time all electrons Matrix
RMS_<electrode> RMS time all electrons Matrix
MEAN<electron>_<electrode> mean time selected electron Matrix
MEDIAN<electron_<electrode> median time selected electron Matrix
RMS<electron>_<electrode> RMS time selected electron Matrix
E_<electron> sequence # selected electron Number

The string "<electrode>" in the global variable name is set to 1 for the first selected electrode, 2 for the next etc.

The string "<electron>" is an index that runs from 1 to the number of selected electrons. E_<electron> shows which electron a given index corresponds to. This can be zero or a negative number: 0 means the last electron, -1 the one but last etc.

You have to declare the Global variables before the loop if

Declaring is not required if the variables are only used outside the loop, in procedure Calls, in Say statements or for substitution in normal input statements.

[This option is not on by default, but its setting is remembered from one call to the next.]

iterations

The number of Monte Carlo loops over track generation. These loops consume relatively little CPU time since the drift times, diffusion coefficients etc are all taken from interpolation tables.

It seems therefore tempting to select a large value for this parameter. When saving the distributions (KEEP-HISTOGRAMS) and then using them in a fit, this may indeed be a good approach. However, when extracting information from the MC process with means and RMS, the accuracy tends to degrade for large values of loop, mainly because of single entries with are far from the mean.

When specifying SINGLE-CLUSTER, only one cluster is generated per track, as a result the default value will be low and you are advised to choose a larger value in this case.

[Default: initially 1000. Each ARRIVAL statement has as default the value set in the previous invocation.]

order

The time by which the selected electron has a certain probability to have arrived, is obtained by reverse polynomial interpolation in the cumulative timing histogram. Using this keyword, you can change the order of the polynomial.

For the lower orders, you may also specify the keywords LINEAR, QUADRATIC or PARABOLIC and CUBIC.

Although values between 1 and 10 are accepted, orders larger than 2 are not recommended since they tend to lead to oscillation.

[Default: 2, parabolic interpolation. The setting will be remembered from one call to the next.]

DATASET

Requests output of a summary of the calculations to a dataset.

[Dataset output is only done on request.]

Additional information on:

 

plot_options

You have control over the volume of the graphics output with the plot options.

The PLOT-SELECTED-ELECTRONS and PLOT-ALL-ELECTRONS options tend to lead to very bulky output, but these plots can be instructive.

Additional information on:

 

print_options

These options provide the same output as the plot_options, but the printout contains additional information such as the mean and RMS. These quantities are computed from the entries themselves, not from the accumulated bin contents. The internal arithmetic is done in double precision.

[The setting is remembered from one call to the next.]

Additional information on:

 
Go to the top level, to &DRIFT, to ARRIVAL-TIME-DISTRIBUTION, to the topic index, to the table of contents, or to the full text.

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