&DRIFT

overview

The instructions of the drift section fall in 4 categories:

setting various parameters
calibration
display of drift behaviour
service instructions

This is probably the most intensively used section of Garfield. Before loops and procedure calls became available, many requests for instructions that are variations on existing instructions were made. This has lead to a fair amount of duplication among the instructions.

Setting parameters:

Command	Short description
`AREA`	Sets the size and view of the drift area
`GRID`	Grid density for tables and contour plots
`INTEGRATION-PARAMETERS`	Accuracy of diffusion, Townsend integration
`LINES`	Number of drift-lines used by x(t) etc.
`OPTIONS`	Debugging options
`SELECT`	Selection of sense wires
`TRACK`	Sets the particle trajectory

Calibration:

Command	Short description
`ARRIVAL-TIME-DISTRIBUTION`	x(t) Relations, detailed calculation
`MINIMISE`	Search for the minimum of a function
`TABLE`	Produces a drift time table
`TIMING`	Arrival time distributions for 2D areas
`XT-PLOT`	x(t) Relations, simple variant

Display drift behaviour:

Command	Short description
`CLUSTERING-HISTOGRAMS`	Makes histograms of the cluster statistics
`DRIFT`	Plots drift-lines and isochrons
`GRAPHICS-INPUT`	Graphics menu driven drift-line plotting
`LORENTZ-ANGLE`	Prints the Lorentz angle at a given point
`PLOT-FIELD`	Plots drift related quantities
`SINGLE`	Graphs for a single drift-line
`SPEED`	Prints the drift speed at a given point
`TIME`	Timing of drift-line calculation

Service instructions:

Command	Short description
`GET-TRACK`	Retrieves a prepared track from a file
`PREPARE-TRACK`	Prepares a track of interpolation
`WRITE-ISOCHRONS`	Writes the set of isochrons to a file
`WRITE-TRACK`	Writes a prepared track to a file

Note: There are procedures that perform drift related tasks: AVALANCHE, DRIFT_ELECTRON, DRIFT_ELECTRON_3, DRIFT_MC_ELECTRON, DRIFT_POSITRON, DRIFT_POSITRON_3, DRIFT_MC_POSITRON, DRIFT_ION, DRIFT_ION_3, DRIFT_MC_ION, DRIFT_MC_NEGATIVE_ION, DRIFT_NEGATIVE_ION, DRIFT_NEGATIVE_ION_3, DRIFT_INFORMATION, GET_CLUSTER, GET_DRIFT_LINE, NEW_TRACK, PLOT_DRIFT_AREA, PLOT_DRIFT_LINE, PLOT_TRACK, PRINT_DRIFT_LINE and RND_MULTIPLICATION.

The FIT_GAUSSIAN procedure can be of use when studying the output of the ARRIVAL-TIME-DISTRIBUTION instruction.

methods

Garfield currently has 4 different integration techniques:

The above plot illustrates the difference between Monte Carlo and Runge Kutta Fehlberg drifting. In this symmetric chamber, 20\ electrons are drifted, from a point, using the Monte Carlo algorithm in the upper half and using Runge Kutta Fehlberg integration in the lower half.

The plot has been made with the following commands:

area -0.11 -0.11 0.11 0.11
int-par mc-dist-int 0.001
Call plot_drift_area
For i From 1 To 20 Do
   Call drift_mc_electron(0.005,0.09,0)
   Call plot_drift_line
Enddo
Call drift_electron(0.005,-0.09)
Call plot_drift_line
Call plot_end

Additional information on:

velocity	Runge_Kutta_Fehlberg
Monte_Carlo	microscopic
vacuum	diffusion
multiplication	attachment
status

AREA

Changes the area in which electrons and ions are allowed to drift. This is also the part of the chamber that is plotted.

Formats:

See the AREA command in the field section.

ARRIVAL-TIME-DISTRIBUTION

Computes the arrival time distribution of the n'th electron that reach electrodes from a series of tracks. A by-product of this calculation is the x(t) relation and an estimate of the arrival time spread. See XT-PLOT for a comparison with related commands.

Before issuing this command, you should take care of the following:

The drift AREA should be set sufficiently large that all points from which electrons can reach a selected electrode are inside. The viewing plane and the projection are not used by the present command - they can be set in a manner which facilitates examining the drift paths.
This command overwrites the geometrical track information but makes use of the clustering model. Since the default clustering model is not meaningful in the present context, the TRACK command should be used to select e.g. Heed clustering.
When using Heed clustering, ensure that the COMPUTE-IF-INTERPOLATION-FAILS integration parameter is active. This command prepares an interpolation table for points on the track while Heed may generate ionisation electrons that are not located on the track (e.g. \δ-electrons).
Only selected electrodes are considered by this command. The SELECT command can be used to examine and modify the selection. Electrode grouping has no effect on the present command.
The PROGRESS-PRINT global option enables you to follow the progress of the calculations.
The DRIFT-PLOT option is of use to verify that the tracks cover the desired part of the chamber and that the electrons really reach the electrodes.

By default, this command operates in the x-y plane, but it can also work in the y-z and z-x planes. The choice is controlled with the STEP and SCAN keywords.

Another important argument is ELECTRON.

Format:

ARRIVAL-TIME-DISTRIBUTION ...
     [ELECTRON {electron | LAST | ONE-BUT-LAST | ... }] ...
     [THRESHOLD threshold] ...
     [TIME-WINDOW {AUTOMATIC | FULL-RANGE | tmin tmax }] ...
     [STEP {X | Y | Z} ...
           [RANGE umin umax] ...
           [INCREMENT ustep]] ...
     [SCAN {X | Y | Z} ...
           [RANGE vmin vmax] ...
           [ANGLE phi]] ...
     [OFFSET w] ...
     [LINES lines] ...
     [DIFFUSION | NODIFFUSION] ...
     [ATTACHMENT | NOATTACHMENT] ...
     [DATASET file [member]] [REMARK remark] ...
     [BINS bins] ...
     [ITERATIONS iterations] ...
     [POLYNOMIAL-ORDER order] ...
     [NOKEEP-HISTOGRAMS | KEEP-HISTOGRAMS] ...
     [NOKEEP-RESULTS | KEEP-RESULTS] ...
     [NOPLOT-ALL-ELECTRONS | PLOT-ALL-ELECTRONS] ...
     [NOPLOT-SELECTED-ELECTRONS | PLOT-SELECTED-ELECTRONS] ...
     [NOPRINT-ALL-ELECTRONS | PRINT-ALL-ELECTRONS] ...
     [NOPRINT-SELECTED-ELECTRONS | PRINT-SELECTED-ELECTRONS] ...
     [PLOT-OVERVIEW | NOPLOT-OVERVIEW]
     [PRINT-OVERVIEW | NOPRINT-OVERVIEW]

If you don't manage to fit all this on a single line, remember that an instruction can be split over several lines by putting an ellipsis at the end of each line but the last.

Example:

track exponential
arrival electron 5 last dataset "arrival/electron.5" thresh 0.8

The track type is set to EXPONENTIAL-SPACING, i.e. the mean number of clusters per cm and the cluster size distribution from the gas section are used. One could also ask for HEED, to simulate a particle. The arrival time distribution of the 5th and of the last electron are computed. A file is written that contains the the time by which 80\ % of these electrons have reached the electrode.

Additional information on:

plane	electron
threshold	TIME-WINDOW
STEP	SCAN
OFFSET	DIFFUSION
ATTACHMENT	LINES
bins	KEEP-HISTOGRAMS
KEEP-RESULTS	iterations
order	DATASET
plot_options	print_options

CLUSTERING-HISTOGRAMS

Makes a set of histograms that show some aspects of the cluster statistics:

distance between electrons and track
number of clusters on the track
number of electrons on the track
energy in each cluster (if available)
total energy loss over the track (if available)

These histograms are of use mainly if Heed is used to generate tracks. Keep the following in mind in this respect:

Heed, internally, doesn't have a concept of clusters. Most electrons that are deposited in the gas stem from "virtual gammas" which ionise a gas molecule by liberating electrons that may (\δ-electrons) or may not have enough energy to ionise further gas molecules.
When you use the NODELTA-ELECTRONS option of TRACK, then all electrons that stem from a single virtual photon are placed at the location where the virtual photon was absorbed, thus creating a cluster. Such a cluster will usually be located very close to the track. With this option, the cluster size distribution is of interest, but the distance between track and electrons is meaningless.
When you use the DELTA-ELECTRONS option of TRACK, then each electron generated by Heed is dealt with as a cluster of size 1. The electrons will usually be located further from the track than the virtual photons. With this option, the cluster size distribution is of no interest, while the distribution between track and electrons reflects the range of \δ-electrons.
When using the MULTIPLE-SCATTERING option of TRACK, which is not default, then the distance between electrons and track is measured with respect to the average trajectory, i.e. the trajectory of the particle if there were no multiple scattering.

Format:

CLUSTERING-HISTOGRAMS ...
     [ITERATIONS  iter] ...
     [BINS  bins] ...
     [CLUSTER-SIZE-BINS  bins] ...
          [CLUSTER-SIZE-RANGE  {AUTOMATIC | min max}] ...
     [CLUSTER-COUNT-BINS  bins] ...
          [CLUSTER-COUNT-RANGE  {AUTOMATIC | min max}] ...
     [CLUSTER-ENERGY-BINS  bins] ...
          [CLUSTER-ENERGY-RANGE  {AUTOMATIC | min max}] ...
     [DELTA-RANGE-BINS  bins] ...
          [DELTA-RANGE-RANGE  {AUTOMATIC | min max}] ...
     [TRACK-RANGE-BINS  bins] ...
          [TRACK-RANGE-RANGE  {AUTOMATIC | min max}] ...
     [ENERGY-LOSS-BINS  bins] ...
          [ENERGY-LOSS-RANGE  {AUTOMATIC | min max}] ...
     [NOKEEP-HISTOGRAMS | KEEP-HISTOGRAMS] ...
     [PLOT-HISTOGRAMS | NOPLOT-HISTOGRAMS]

Additional information on:

iter	bins
range	KEEP-HISTOGRAMS
PLOT-HISTOGRAMS

DRIFT

This instruction makes plots of electron and ion drift-lines and can also plot isochrons.

The main choice is between the 5 kinds of starting points:

the EDGES of the AREA;
the TRACK;
the surface of selected SOLIDS
the surface of selected WIRES;
the ZEROES of the electrostatic field.

Each has a set of sub-options that should follow the EDGES, SOLIDS, WIRES, TRACK or ZEROES keyword. The other options should be placed at the end of the line.

Format:

DRIFT {EDGES  [LEFT | NOTLEFT] ...
              [RIGHT | NOTRIGHT] ...
              [UP | NOTUP] ...
              [DOWN | NOTDOWN] ...
              [LINES lines]                                    | ...
       TRACK  [NOTIME-GRAPH | TIME-GRAPH] ...
              [NOVELOCITY-GRAPH | VELOCITY-GRAPH] ...
              [NODIFFUSION-GRAPH | DIFFUSION-GRAPH] ...
              [NOAVALANCHE-GRAPH | AVALANCHE-GRAPH] ...
              [NOFUNCTION-GRAPH | FUNCTION-GRAPH function] ...
              [MARKER | SOLID]                                 | ...
       SOLIDS [LINES lines]                                    | ...
       WIRES  [LINES lines] ...
              [ANGLE-RANGE amin amax]                          | ...
       ZEROES                                                    } ...

       [RUNGE-KUTTA-DRIFT | MONTE-CARLO-DRIFT] ...
       [NOISOCHRONS | ISOCHRONS delta_t] ...
       [REVERSE-ISOCHRONS | NOREVERSE-ISOCHRONS] ...
       [LINE-PLOT | NOLINE-PLOT] ...
       [NOLINE-PRINT | LINE-PRINT] ...
       [ELECTRON | ION] ...
       [NEGATIVE | POSITIVE]

If you don't manage to fit all this on one line, remember you are allowed to abbreviate. A line that ends on an ellipsis continues on the next line.

Examples:

drift wires lines=25 isochrons 0.1 nol-pl
drift track function-graph time+5*diffusion nol-pl l-pr
drift zero

(The first example will plot only a set of isochrons computed using 25 drift-lines from each of the selected wires. The second example prints a table of drift times etc. and plots the drift time plus five times the diffusion. The last example shows the acceptance boundaries.)

Additional information on:

EDGES	SOLIDS
WIRES	TRACK
ZEROES	RUNGE-KUTTA-DRIFT
MONTE-CARLO-DRIFT	ISOCHRONS
REVERSE-ISOCHRONS	LINE-PLOT
LINE-PRINT	ELECTRON
ION	POSITIVE
NEGATIVE	representations

GET-TRACK

Retrieves a prepared track from a dataset written by WRITE-TRACK. This saves time since one doesn't have to run PREPARE-TRACK again.

Format:

GET-TRACK file [member]

Example:

get-tr lib

(This call will retrieve the first prepared track in the dataset LIB.DAT, which may contain members of different type as well.)

Additional information on:

file

member

GRAPHICS-INPUT

Enters a graphics menu driven mini drift section. The edges of the AREA and the TRACK can very easily be changed by simply pointing to them. Typical calculations include a single drift-line from a point indicated on the screen, drift-lines from the TRACK and drift-lines from a wire (and its periodic repetitions) selected on the screen.

You have some control over the graphics input mode with the options listed below.

Format:

GRAPHICS-INPUT [CHOICE-PET chpet] [LOCATOR-PET locpet1 locpet2] ...
               [PICK-PET pickpet] [VALUATOR-PET valpet] ...
               [CHOICE-DEVICE chdev] [LOCATOR-DEVICE locdev] ...
               [PICK-DEVICE pickdev] [VALUATOR-DEVICE valdev] ...
               [WORK-STATION wkid]

Example:

gra loc-pet 1 4

Chooses rubber band for the second point.

Additional information on:

prompt_echo	device
WORK-STATION

GRID

Chooses the x (or r) and y (or \φ) density of the grid inside the AREA from which instructions like TABLE will calculate drift-lines.

The grid is common to all sections.

Format:

GRID  number_of_steps_in_x  [number_of_steps_in_y]

Example:

grid 10 20

Additional information on:

number

INTEGRATION-PARAMETERS

Enables one to change the following:

the Runge Kutta Fehlberg drift-line integration accuracy and maximum step length;
the step size for Monte Carlo drifting;
the range of permitted diffusion scaling factors in Monte Carlo drifting;
the distance from a wire where a electron or ion is considered to be caught by the wire;
the order with which drift-lines are interpolated when using prepared tracks;
the distance at which the integration algorithm for transverse + longitudinal diffusion projects the cloud radially onto the wire;
the method by which the cloud is projected into the wire;
the maximum stack depth and the relative accuracy of the integration of the diffusion coefficient, the Townsend coefficient and the attachment coefficient;
conditions under which isochron segments are joined;
appearance of isochrons.

These parameters are used both in this section and in the signal section.

Format:

INTEGRATION-PARAMETERS ...
     [INTEGRATION-ACCURACY accuracy ] ...
     [ MAXIMUM-STEP-LENGTH maximum_step | ...
       NOMAXIMUM-STEP-LENGTH ] ...
     [ MONTE-CARLO-MAXIMUM-TIME maximum_time | ...
       NOMONTE-CARLO-MAXIMUM-TIME ] ...
     [ MONTE-CARLO-TIME-INTERVAL step_size ...
       MONTE-CARLO-DISTANCE-INTERVAL step_size ...
       MONTE-CARLO-COLLISIONS step_size ] ...
     [ DIFFUSION-SCALING-RANGE scale_min scale_max ] ...
     [ CHECK-ATTRACTING-WIRES | ...
       CHECK-ALL-WIRES ] ...
     [ REJECT-KINKS | ...
       NOREJECT-KINKS ] ...
     [TRAP-RADIUS ntrap] ...
     [INTERPOLATION-ORDER order] ...
     [ COMPUTE-IF-INTERPOLATION-FAILS | ...
       ABANDON-IF-INTERPOLATION-FAILS ] ...
     [CLOUD-PROJECTION-DISTANCE ncloud] ...
     [CLOUD-PROJECTION-METHOD ...
         { CENTRAL-VELOCITY-INTEGRATION | ...
           INTEGRATION | ...
           LONGITUDINAL-DIMENSION | ...
           LARGEST-DIMENSION | ...
           NO-PROJECTION } ...
     [DIFFUSION-ACCURACY \&epsilon;_diff] ...
     [TOWNSEND-ACCURACY \&epsilon;_Town] ...
     [ATTACHMENT-ACCURACY \&epsilon;_att] ...
     [DIFFUSION-STACK-DEPTH stack_diff] ...
     [TOWNSEND-STACK-DEPTH stack_Town] ...
     [ATTACHMENT-STACK-DEPTH stack_att] ...
     [PROJECTED-PATH-INTEGRATION | ...
       TRUE-PATH-INTEGRATION ] ...
     [ DRAW-ISOCHRONS | ...
       MARK-ISOCHRONS ] ...
     [ SORT-ISOCHRONS | ...
       NOSORT-ISOCHRONS ] ...
     [ ISOCHRON-CONNECTION-THRESHOLD iso_thr | ...
       NOISOCHRON-CONNECTION-THRESHOLD ] ...
     [ISOCHRON-ASPECT-RATIO-SWITCH iso_aspect] ...
     [ISOCHRON-LOOP-THRESHOLD iso_loop] ...
     [ CHECK-ISOCHRON-CROSSINGS | ...
       NOCHECK-ISOCHRON-CROSSINGS ]

Example:

int diff-st 5, diff-acc 1.0e-3

Will limit the number of subdivisions to 32 per drift-line step (the default is usually 2\<SUP\>20\</SUP\>) and asks for a relative precision per step of one per mille.

Additional information on:

LINES

Sets the default number of drift-lines for a couple of commands such as track preparation. The parameter also governs in part the accuracy of the x(t) calculation in sets the number of drift-lines used for the initial crude search for the optimal point in y for each x.

Please note that LINES has no effect anymore on the DRIFT command. For DRIFT TRACK, use the TRACK command to set a clustering model. For DRIFT EDGES, DRIFT SOLIDS and DRIFT WIRES, use the respective LINES option on the DRIFT command line.

Format:

LINES lines

Example:

lines 50

LORENTZ-ANGLE

Prints the Lorentz-angle, i.e. the angle between the drift vector and the electric field, at the point (x,y,z).

This command is now superseded by the LORENTZ_ANGLE procedure.

Format:

LORENTZ-ANGLE x y z

Example:

lorentz 0.5 0.5 1

MINIMISE

Searches for the minimum of e.g. the drift time over a curve.

Format:

MINIMISE f_min ...
         [SELECTION-FUNCTION f_select] ...
         ON f_curve ...
         RANGE t_min t_max ...
         [N n] ...
         [ELECTRON | ION] ...
         [NEGATIVE | POSITIVE] ...
         [FUNCTION-PRECISION \&epsilon;_f] ...
         [POSITIONAL-RESOLUTION \&epsilon;_pos] ...
         [ITERATE-LIMIT itermax] ...
         [PRINT | NOPRINT] ...
         [DATASET dataset [member] [REMARK remark]]

Example:

minimise time on '5*cos(t), 5*sin(t)' range {pi/4,3*pi/4}

This instruction asks for a minimisation of the drift time over an arc with radius 5 and in the angular range pi/4 to 3 pi/4. Note that quotes are used to specify the curve: a comma has to be placed between the two coordinates, but since the comma is one of the separators and since ON expects only one element, quotes are used. RANGE on the other hand expects two elements and quotes should therefore not be used !

Additional information on:

f_min	f_select
ON	RANGE
N	ELECTRON
ION	POSITIVE
NEGATIVE	FUNCTION-PRECISION
POSITIONAL-RESOLUTION	ITERATE-LIMIT
PRINT	DATASET

OPTIONS

Determines whether the drift-lines produced by other commands than the DRIFT instruction are plotted or printed. Commands affected by these options include ARRIVAL-TIME-DISTRIBUTION and PREPARE-TRACK. The option is also honoured in the debugging mode of several other commands.

You may also change global options in the same statement, see the top level OPTIONS command for further information.

Format:

OPTIONS [DRIFT-PRINT | NODRIFT-PRINT] ...
        [DRIFT-PLOT | NO-DRIFT-PLOT] ...
        [KEY | NOKEY] ...
        [CONTOUR-ALL-MEDIA | CONTOUR-DRIFT-MEDIUM] ...
        [NOWIRE-MARKERS | WIRE-MARKERS] ...
        [NOCHECK-MAP-INDICES | CHECK-MAP-INDICES]

Example:

opt dr-pl nodr-pr

Additional information on:

DRIFT-PRINT	DRIFT-PLOT
KEY	CONTOUR-ALL-MEDIA
CONTOUR-DRIFT-MEDIUM	WIRE-MARKERS
CHECK-MAP-INDICES

PLOT-FIELD

This instruction plots the quantities related to drifting of electrons and ions in a variety of ways, such as contours, a surface plot, a graph, an histogram.

Similar instructions exist in the field and signal sections.

CPU time can be saved if several plots are combined in a single command.

Format:

PLOT-FIELD [CONTOUR [f1]   [RANGE {cmin cmax | AUTOMATIC}] ...
                           [N n] ...
                           [LABELS | NOLABELS]] ...
           [GRAPH [f2]     [ON f_curve] ...
                           [N n]] ...
                           [SCALE min max] ...
                           [NOPRINT | PRINT] ...
           [HISTOGRAM [f3] [RANGE {hmin hmax | AUTOMATIC}] ...
                           [BINS nbin]] ...
           [SURFACE [f4]   [ANGLES \&phi; \&theta;]] ...
           [VECTOR [f5 f6 [f7]]] ...
           [RUNGE-KUTTA-DRIFT | MONTE-CARLO-DRIFT] ...
           [ELECTRON | ION] ...
           [POSITIVE | NEGATIVE]

If you don't manage to fit all this on a single line, remember that lines that end on an ellipsis are continued on the next.

Examples:

plot hist diffusion vector vdx, vdy surf cont
plot contour time range 0.1 0.3

(The first example makes most of the plots using default functions and ranges - useful as a first call. The second example makes a more detailed contour plot.)

Additional information on:

f	CONTOUR
GRAPH	HISTOGRAM
SURFACE	VECTOR
ELECTRON	ION
POSITIVE	NEGATIVE
RUNGE-KUTTA-DRIFT	MONTE-CARLO-DRIFT

PREPARE-TRACK

Calculates and stores an interpolation table for drift-line related quantities. Prepared tracks are used e.g. when in a Monte Carlo calculation drift times are needed at many randomly located points on one track. The difference in CPU time usage can be dramatic while the loss in accuracy is usually negligible.

Interpolation of tracks is currently done in 3 cases:

the ARRIVAL-TIME-DISTRIBUTION command uses prepared tracks, but performs the preparation itself;
prepared tracks are used in signal simulations, provided the INTERPOLATE-TRACK option has been switched on, and provided the user has performed a track preparation;
in user procedures that call INTERPOLATE_TRACK.

The track thus prepared, can be saved in a dataset with WRITE-TRACK from where it can be retrieved in subsequent runs with GET-TRACK.

Format:

PREPARE-TRACK ...
     [ATTACHMENT-COEFFICIENT | NOATTACHMENT-COEFFICIENT] ...
     [DIFFUSION-COEFFICIENT | NODIFFUSION-COEFFICIENT] ...
     [TOWNSEND-COEFFICIENT | NOTOWNSEND-COEFFICIENT] ...
     [LINES n]

Example:

prep-tr

(Accept all defaults, usually adequate.)

Additional information on:

ATTACHMENT-COEFFICIENT	DIFFUSION-COEFFICIENT
TOWNSEND-COEFFICIENT	LINES

SELECT

Selects and groups the electrodes which are to be handled specially. The selection is common to all sections, but the interpretation of the selection is left to the individual instructions.

The grouping is of no importance in this section. The selection determines for instance which wires are processed by DRIFT WIRES, ARRIVAL-TIME-DISTRIBUTION and XT-PLOT.

Format:

See SELECT

Example:

sel (1 s) 2 f

(Put wire 1 together with all S wires in one group, make wire 2 a group of its own and do the same for each of the F wires.)

SINGLE

An instruction that will print and plot details about a single drift-line from (x,y). The information can be presented as a table of the position, the integrated drift time and a user specified function, but also as a graph of one function against another.

Similar plots can be obtained by first computing a drift-line with the DRIFT_ELECTRON, DRIFT_ELECTRON_3, DRIFT_MC_ELECTRON, DRIFT_POSITRON, DRIFT_POSITRON_3, DRIFT_MC_POSITRON, DRIFT_ION, DRIFT_ION_3, DRIFT_MC_ION, DRIFT_MC_NEGATIVE_ION, DRIFT_NEGATIVE_ION or DRIFT_NEGATIVE_ION_3 procedure, then retrieving it with GET_DRIFT_LINE and finally making the graph with PLOT_GRAPH.

Format:

SINGLE  FROM  x y ...
        [PLOT f1 VS f2 | NOPLOT] ...
        [PRINT f3 | NOPRINT] ...
        [NEGATIVE | POSITIVE] ...
        [ELECTRON | ION]

Examples:

single from 0.5 0.3 plot diffusion vs path
single from 0.1 0.2 print vdx

Additional information on:

f	PRINT
PLOT	ELECTRON
ION	POSITIVE
NEGATIVE

SPEED

A debugging instruction that will evaluate the drift speed at a given point (x,y,z). The POSITIVE or NEGATIVE keyword should, if used, be placed after the ELECTRON or ION keyword, if used.

Similar functionality is provided by the ELECTRON_VELOCITY and ION_VELOCITY procedures.

Format:

SPEED x y z   [ELECTRON | ION]   [NEGATIVE | POSITIVE]

Example:

speed 0.5 1.5 0

TABLE

Prints a table of drift times for electrons or ions starting from a GRID of regularly spaced points inside the AREA.

The POSITIVE or NEGATIVE keyword should, if used, be at the end of the command.

Format:

TABLE [TABLE | NOTABLE] ...
      [NOCONTOUR | CONTOUR] ...
      [ELECTRON | ION] ...
      [NEGATIVE | POSITIVE]

This command must be entered on a single line !

Example:

table

(Only produce the table, no contours.)

Additional information on:

TABLE

CONTOUR

TIME

Times n drift-line calculations [default: 10].

Format:

TIME [n]

Example:

time 5

TIMING

Computes the arrival time distribution of the n'th electron over a given area. Unlike the ARRIVAL-TIME-DISTRIBUTION instruction, TIMING does not produce calibration curves, but merely timing distributions.

This instruction overwrites the geometrical part of the track description, but uses the clustering type entered via the TRACK statement.

Format:

TIMING [ELECTRONS {electron | LAST | ONE-BUT-LAST | ... }] ...
       [TIME-WINDOW tmin tmax ] ...
       [X-RANGE xmin xmax]
       [Y-RANGE ymin ymax] ...
       [ANGLE-RANGE phimin phimax] ...
       [BINS bins] ...
       [ITERATIONS loops] ...
       [RUNGE-KUTTA-DRIFT | MONTE-CARLO-DRIFT] ...
       [NOATTACHMENT | ATTACHMENT] ...
       [WEIGHTING-FUNCTION weight] ...
       [NOKEEP-HISTOGRAMS | KEEP-HISTOGRAMS] ...
       [NOPLOT-OVERALL | PLOT-OVERALL] ...
       [NOPLOT-SELECTED-ELECTRON | PLOT-SELECTED-ELECTRON] ...
       [NOPRINT-OVERALL | PRINT-OVERALL] ...
       [NOPRINT-SELECTED-ELECTRON | PRINT-SELECTED-ELECTRON]

If you don't manage to fit all this on a single line, remember that lines that end on an ellipsis are continued on the next.

The PROGRESS-PRINT global option enables you to follow the progress of the computations.

Example:

track muon energy 20 GeV
timing electron 3 last y-range -0.3 +0.3

Computes the arrival time distribution of the 3rd and the last electron for random vertical Heed-generated tracks of 20\ GeV muons in the y range [-0.3,+0.3]. The x-range is default, i.e. the x-portion of the AREA.

Additional information on:

electron	TIME-WINDOW
X-RANGE	Y-RANGE
ANGLE-RANGE	MONTE-CARLO-DRIFT
ATTACHMENT	WEIGHTING-FUNCTION
bins	KEEP-HISTOGRAMS
loops	plot_options
print_options

TRACK

In Garfield, the track is a line in space and a model for generating clusters over this line. The track is widely used, for instance by the PLOT-FIELD command in the field section, the SET command in the optimisation section, the ARRIVAL-TIME-DISTRIBUTION, DRIFT, PLOT-FIELD and TIMING commands in the drift section as well as by the PLOT-FIELD and SIGNAL commands in the signal section. All sections use the same track.

The track definition command has an elaborate format that stems from its broad use. For field plotting and potential optimisation, it is sufficient to enter the track location - for most other applications you should specify a clustering model too:

Location of the track: One can indicate the location of the track in 3 manners:
- Tracks in Garfield are line segments, normally identified by a begin and an end point. This is adequate for drawing graphs, and for high energy particles.
- Low energy particles undergo multiple scattering and may also be stopped in the gas. It is therefore more appropriate to describe these by a starting point and an initial direction. You may also give a begin and end point pair, which will be used to compute an initial direction.
- One may also, for some applications, request a point-track, i.e. a track of which start and end point coincide. This can sometimes be used as a poor approximation of a photon.
Clustering model: Garfield recognises 9 models to distribute clusters or points over the track:
- FIXED-NUMBER: deposition of an electron or ion at regularly spaced intervals. This model is mainly used for making graphs, it has no physical meaning.
- EQUAL-SPACING: deposition of the mean number of clusters as specified in the gas section, at regularly spaced points along the track. This model has no physical meaning, but can be used to estimate the impact of cluster interval fluctuations.
- EXPONENTIAL-SPACING: deposition of clusters of electrons at random locations along the track, respecting the information from the gas section. This model can be accurate, given good quality gas data.
- WEIGHTED-DISTRIBUTION: deposition of electrons or ions over the track such that the positions are distributed according to a user specified function. This model is used to study the impact of background electron or ion sources.
- SINGLE-CLUSTER: a single cluster of electrons is generated per track at a random location along it. This model could be used as a rough approximation of a photon.
- HEED: a simulation of the interactions between the particle and the gas using the Heed program.
- SRIM: a simulation of the interactions between the particle and the gas based on an energy loss table produced by the SRIM program.
- TRIM: a simulation of the interactions between the particle and the gas based on an energy loss table produced by the TRIM program.
- EQUAL-FLUX-INTERVALS: generation of a user determined number of points at equal flux intervals. This model can be used to represent the electric field strength by the spacing of drift-lines.
- CONSTANT-FLUX-INTERVALS: generation of points spaced by a user determined flux interval. This model is used as a crude means to determine the transparency of elements.
- further models can be added on request.

Tracks are 3-dimensional objects. You may omit the z-component of the track, to indicate that the track is located in the (x,y) plane. However, multiple scattering may cause the track to leave this plane and \δ-electrons, Auger electrons and photons are generated irrespective of whether you specify a track located in the (x,y) plane or not.

The model to be used is determined by the last keyword that is found on the line. You may, in a single TRACK statement, set parameters for several models. To avoid ambiguity it is then advisable to type one of the model names (FIXED-NUMBER, EQUAL-SPACING etc) at the end of the line.

Format:

TRACK  [ x0 y0 | x0 y0 x1 y1 | ...
         x0 y0 z0 | x0 y0 z0 x1 y1 z1 | ...
         FROM x0 y0 [z0] | ...
         { TO x1 y1 [z1] | DIRECTION dx dy [dz] RANGE range } ] ...
       [ FIXED-NUMBER ]  ...
            [ LINES nline ]                    | ...
       [ EQUAL-SPACING ]                       | ...
       [ EXPONENTIAL-SPACING ]                 | ...
       [ SINGLE-CLUSTER ]                      | ...
       [ WEIGHTED-DISTRIBUTION ] ...
            [ WEIGHTING-FUNCTION { f | weight vs coordinate } ] ...
            [ SAMPLES nsample ]                | ...
       [ HEED ] ...
            [ DELTA-ELECTRONS | NODELTA-ELECTRONS ] ...
            [ TRACE-DELTA-ELECTRONS | NOTRACE-DELTA-ELECTRONS ] ...
            [ NOMULTIPLE-SCATTERING | MULTIPLE-SCATTERING ] ...
            [ NOENERGY-CUT | ENERGY-CUT ] ...
            [ SWITCH-ELECTRON-TO-CHARGED eswitch ] ...
            [ particle | MASS mass CHARGE charge ] ...
            [ ENERGY energy ]                  | ...
       [ SRIM ] ...
            ENERGY energy ...
            [ particle | MASS mass CHARGE charge ] ...
            [ FLUCTUATION-MODEL model ] ...
            [ LATERAL-STRAGGLING | NOLATERAL-STRAGGLING] ...
            [ LONGITUDINAL-STRAGGLING | NOLONGITUDINAL-STRAGGLING] ...
            [ FAST-VAVILOV | PRECISE-VAVILOV] ...
            [ GROUPING [AUTOMATIC | NONE | n_e ]]     | ...
       [ TRIM ] ...
       [ EQUAL-FLUX-INTERVALS ] ...
            [ FLUX-LINES n]                    | ...
       [ CONSTANT-FLUX-INTERVALS ] ...
            [ FLUX-INTERVAL dv]

Examples:

track * * * 5

Keep all old values except the y coordinate of the end point.

track 1 1 1 2 2 2

Defines a track from (1,1,1) to (2,2,2).

track from 1 1 1 direction 0 0 1 range 5
track mu+ energy 10 GeV lines 10 multiple-scattering nodelta
track fixed
drift track
track heed
drift track

In a first TRACK statement, the location of the track is described. The length of the track projected onto the DIRECTION is limited to 5\ cm. The second TRACK statement provides HEED with a description of the particle, indicates that multiple scattering should be taken into account, but not \δ-electrons. The same line changes the default number of deposits for the FIXED-NUMBER model to 10. The third TRACK statement selects the model to be used, a plot is made with this model, the model is then changed to HEED and another plot is produced.

Additional information on:

FROM	TO
DIRECTION	RANGE
FIXED-NUMBER	EQUAL-SPACING
EXPONENTIAL-SPACING	WEIGHTED-DISTRIBUTION
SINGLE-CLUSTER	HEED
EQUAL-FLUX-INTERVALS	SRIM
TRIM	CONSTANT-FLUX-INTERVALS
representations

XT-PLOT

Produces an x(t) plot: the relation between the position of a track and the drift time. This is a calibration curve used by the track reconstruction program.

The XT-PLOT algorithm works as follows:

From around the SELECTed wires, a number of drift lines are computed (see LINES) drifting them backwards from the wire.
The crossing points of these drift-lines are determined with a series of lines at an angle to the y-axis and crossing the x-axis at regular intervals between xmin and xmax spaced by xstep. The lines will be referred to as 'minimisation lines'. For each of the crossing points, the drift time is interpolated on the drift-line.
On a subset (see jump) of the minimisation lines the 3 smallest drift times are kept, drift-lines from the corresponding crossing points are computed to enhance the accuracy of the time estimate, and these 3 points are then used as start for a parabolic minimisation procedure with a limited number of iterations (see the itermax) and which is declared to converge if the minimum drift time doesn't change much (see \ε).
The results are printed (see PRINT-XT-RELATION), plotted (see PLOT-XT-RELATION and SCALE) and output to a dataset (see DATASET).

Note that there is another instruction in Garfield, ARRIVAL-TIME-DISTRIBUTION, that serves approximately the same purpose. The differences between XT-PLOT and ARRIVAL are summarised in the table below. As can be seen from the table, ARRIVAL provides more detail than XT-PLOT, which in return is faster.

For accurate calibration, the use of signals is recommended. This permits, in addition to all the features ARRIVAL, processing of the signals by electronics and the setting of a true threshold.

-----------------------------------------------------------------------
Aspect    ARRIVAL                        XT-PLOT
-----------------------------------------------------------------------
input     complete gas tables,           drift velocity and optionally
          clustering properties          diffusion and Lorentz angle
          (spacing, cluster size)        tables
method    Monte Carlo generation of      parabolic minimisation of the
          tracks with clusters           drift time over lines
included  drift velocity, Lorentz        drift velocity, Lorentz angle,
          angle, diffusion, attachment,  optionally also diffusion
          cluster spacing and size       over the fastest drift-line
output    mean, median and RMS of        minimum drift time, diffusion
          selected electrons             over the fastest drift-line
-----------------------------------------------------------------------

Format:

XT-PLOT [DATASET file [member] [REMARK remark] ...
        [ANGLE angle] ...
        [X-RANGE xmin xmax] ...
        [X-STEP xstep] ...
        [JUMP jump] ...
        [ITERATIONS {YES|NO|itermax}] ...
        [PRECISION \&epsilon;] ...
        [LEFT-ANGLE-RANGE lmin lmax] ...
        [RIGHT-ANGLE-RANGE rmin rmax] ...
        [PRINT-XT-RELATION | NOPRINT-XT-RELATION] ...
        [PLOT-XT-RELATION | NOPLOT-XT-RELATION] ...
        [KEEP-RESULTS | NOKEEP-RESULTS] ...
        [SCALE min max]

Examples:

xt-plot
xt dataset lib.dat xt1 precision 1e-2

(The second example will produce fairly quickly a crude x(t).)

Additional information on:

DATASET	angle
xmin	xmax
xstep	jump
itermax	\ε
angle_range	PRINT-XT-RELATION
PLOT-XT-RELATION	KEEP-RESULTS
SCALE

WRITE-ISOCHRONS

Use this command to write out the coordinates of the points used for the isochrons as a result of the last DRIFT command.

This statement should be issued after the DRIFT command.

Format:

WRITE-ISOCHRONS DATASET file [member] [REMARK remark]

Example:

wr-iso 'test data b'

(Writes the isochrons to the VM/CMS dataset TEST DATA on the users B disk.)

Additional information on:

file	member
remark

WRITE-TRACK

Once a track has been prepared with PREPARE-TRACK, it can be written to a dataset for later retrieval with GET-TRACK.

Format:

WRITE-TRACK DATASET file [member] [REMARK remark]

Example:

wr-tr 'disk$scratch:[pubzh.work.garfield]track.dat'

Additional information on:

file	member
remark

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

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

accuracy	maximum_step
maximum_time	step_size
scale	TRAP-RADIUS
order	COMPUTE-IF-INTERPOLATION-FAILS
CHECK-ALL-WIRES	CHECK-ATTRACTING-WIRES
REJECT-KINKS	ncloud
method	\ε
stack	PROJECTED-PATH-INTEGRATION
DRAW-ISOCHRONS	MARK-ISOCHRONS
SORT-ISOCHRONS	ISOCHRON-CONNECTION-THRESHOLD
ISOCHRON-ASPECT-RATIO-SWITCH	ISOCHRON-LOOP-THRESHOLD
CHECK-ISOCHRON-CROSSINGS