&GAS


overview

  The set of useful instructions in the gas section depends of the origin
  of the gas data:

  - gas mixture prepared during the run
  - fully user specified gas mixture
  - built-in gas mixtures with fixed proportions
  - retrieval of a gas description previously stored

  A couple of instructions can be used regardless of the origin.

  ------------------------------------------------------------------------
  Gas mixture prepared during the run
  ------------------------------------------------------------------------
  ADD                        Adds/replaces elements of the transport table
  CLUSTER                    Enters the cluster size distribution
  EXTRAPOLATIONS             Extrapolation of the gas tables
  HEED                       Prepares cluster generation by Heed
  INTERPOLATIONS             Interpolation method in the gas tables
  MAGBOLTZ                   Magboltz gas mixture (accurate)
  MIX                        Schultz-Gresser gas mixing (approximate)
  PARAMETERS                 Molecular parameters of the gas mixture
  PRESSURE                   Sets the pressure
  TEMPERATURE                Sets the temperature
  WRITE                      Stores the gas description

  ------------------------------------------------------------------------
  User specified gas mixture
  ------------------------------------------------------------------------
  ADD                        Adds/replaces elements of the transport table
  CLUSTER                    Enters the cluster size distribution
  EXTRAPOLATIONS             Extrapolation of the gas tables
  GAS-IDENTIFIER             Adds a label to the gas description
  INTERPOLATIONS             Interpolation method in the gas tables
  PARAMETERS                 Molecular parameters of the gas mixture
  PRESSURE                   Sets the pressure
  RESET                      Erases gas data entered sofar
  TABLE                      Enters the gas tables
  TEMPERATURE                Sets the temperature
  WRITE                      Stores the gas description

  ------------------------------------------------------------------------
  Built-in gas mixtures with fixed proportions
  ------------------------------------------------------------------------
  ARGON-20-ETHANE-80         Loads the mixture Argon 20 %, ethane 80 %
  ARGON-50-ETHANE-50         Loads the mixture Argon 50 %, ethane 50 %
  ARGON-80-ETHANE-20         Loads the mixture Argon 80 %, ethane 20 %
  ARGON-73-METHANE-20-PROPANOL-7 Loads Argon 73 %, CH4 20 %, propanol 7 %
  CO2                        Loads data for almost pure CO2
  CO2-80-ETHANE-20           Loads the mixture CO2 80 %, ethane 20 %
  CO2-90-ETHANE-10           Loads the mixture CO2 90 %, ethane 10 %
  CO2-90-ISOBUTANE-10        Loads the mixture CO2 90 %, isobutane 10 %
  ETHANE                     Loads data for pure ethane
  ISOBUTANE                  Loads data for pure isobutane
  METHANE                    Loads data for pure methane
  PRESSURE                   Sets the pressure

  ------------------------------------------------------------------------
  Retrieval of a gas description previously stored
  ------------------------------------------------------------------------
  GET                        Retrieves gas data from a dataset

  ------------------------------------------------------------------------
  General purpose instructions
  ------------------------------------------------------------------------
  OPTIONS                    Plotting and printing of the gas tables
  PLOT-OPTIONS               Selects plots and sets log/lin axes

built_in

  A set of gasses ready for use, supplied by users of the program,
  usually based on private or published measurements. These descriptions
  are provided mainly for rapid studies that do not require high accuracy.

  Please ensure, with the GAS-PRINT and GAS-PLOT options, that the tables
  agree with what you think is reasonable.

  These mixtures have fixed proportions, use MAGBOLTZ or MIX to obtain
  tables for arbitrary proportions.

  Example:

  ARG-50-ETH-50

  (Until further notice, the program will use 50 % Argon, 50 % Ethane.)

Additional Information on:

  • ARGON-20-ETHANE-80
  • ARGON-50-ETHANE-50
  • ARGON-80-ETHANE-20
  • ARGON-73-METHANE-20-PROPANOL-7
  • CO2
  • CO2-80-ETHANE-20
  • CO2-90-ETHANE-10
  • CO2-90-ISOBUTANE-10
  • ETHANE
  • ISOBUTANE
  • METHANE

  • ADD

      Adds/replaces one or more elements to/of the gas table. This
      instruction can be used to add for instance the ion mobility
      to transport tables that have been prepared by Magboltz, but
      can also be used to override the computed parameters with
      measured parameters.
    
      Format:
    
      ADD  item_1 { function_1 | value_1 VS ep_1 [ORDER order] } ...
    
      Example:
    
      Global pbar = 3
      magboltz argon 91 nitrogen 4 methane 5 ...
         n-e/p 100 e/p-range 0.05 135
      Read-vector ep mobility
      <mob.dat
    
      Global mobility=mobility*1e-6*(1.53/1.4)/pbar
      add mobility mobility vs ep
    
      Magboltz is used to generate an electron transport table. This also
      sets the E/p scale. Next, a file is read in that contains mobilities
      as function of E/p for Ar+ ions in Ar at a pressure of 1 atm. The
      data, reproduced below, is taken from the literature. The E/p values
      end up in the matrix EP, while the mobilities go to MOBILITY. Note
      the blank line after the "< mob.dat" statement. The mobility is scaled
      up by 9 % to agree with the currently accepted value at low fields and
      is divided by the pressure. The unit is changed from cm2/sec.V to
      cm2/microsec.V. Finally, the mobility is added to the gas tables using
      the ADD statement.
    
      Mobility for Ar+ in Ar from Landolt-Boernstein vol IV/3 (1957).
    
        0        1.40
        4.       1.40
        5.       1.40
        6.       1.40
        7.       1.40
        8.       1.40
        9.       1.40
       10.000000 1.40
       11.853048 1.40
       14.049476 1.40
       16.652913 1.39
       19.738777 1.380168
       23.396469 1.358125
       27.731947 1.33484
       32.870811 1.270874
       38.961933 1.229374
       46.181767 1.189229
       54.739474 1.150395
       64.882966 1.075413
       76.906092 1.040296
       91.157168 0.972491
      108.049029 0.909105
      128.071041 0.864508
      151.803220 0.808160
      179.933087 0.755485
      213.275570 0.706244
      252.796579 0.649018
      299.641005 0.606716
      355.165921 0.567171
      420.979899 0.521214
      498.989527 0.478981
      591.454687 0.447761
      701.054139 0.404503
      830.962838 0.371727
    

    Additional Information on:

  • item
  • function
  • VS
  • ORDER

  • CLUSTER

      Enters the cluster-size distribution. You may choose between entering
      a parametrisation, listing of all probabilities and a mixture of the
      two formats.
    

    Additional Information on:

  • Parametrisation
  • Listing
  • Mixed

  • EXTRAPOLATIONS

      Indicates how the gas-tables have to be extrapolated to E/p
      values smaller and larger than those present in the table.
    
      The EXTRAPOLATION command has no effect on extrapolation in
      2-dimensional tables, such as those produced by Magboltz when
      the B field is non-zero. For these tables, polynomial
      extrapolation of the order set with the INTERPOLATION command
      will be used for points outside the tabulated ranges.
    
      Format:
    
      EXTRAPOLATIONS item1 method1 item2 method2 ...
    
      Examples:
    
      EXTR DRIFT: LINEAR, DIFF: CONST, TOWN: CONST
      EXTR DRIFT EXP
    

    Additional Information on:

  • item
  • method

  • GAS-IDENTIFIER

      Assigns an identification string to the gas. This string is placed
      on plots when gas data has been used to make the plot.
    
      Format:
    
      GAS-IDENTIFIER string
    
      Example:
    
      GAS-ID "Some gas"
    

    GET

      Retrieves a compact format gas description written by WRITE. This
      command clears gas information you may have entered already. It
      is executed immediately and you may, with caution, replace some
      of the elements of the description after issuing the command.
    
      The compact gas description contains electron transport property
      tables, the ion mobility, cluster size and cluster spacing data,
      Heed initialisation information, the pressure and the temperature.
      GET overwrites all of these.
    
      Format:
    
      GET dsname [member]
    
      Example:
    
      GET gas_data.dat gas2
    

    Additional Information on:

  • dsname
  • member

  • HEED

      Invokes the gas definition part of the Heed program, which simulates
      the energy loss through ionisation of a particle that traverses the
      gas. This initialisation, which is very fast, is mandatory if you
      use Heed in other section to do clustering.
    
      The temperature and the pressure should be specified before issuing
      the HEED command. If the temperature is not specified before the HEED
      command, then a default temperature of 300 K will be used.
    
      Neither temperature nor pressure scaling is applied to the cluster
      information provided by HEED.
    
      The author of Heed, Igor Smirnov, should be contacted for further
      information about this program.
    
      Format:
    
      HEED  [ ARGON  fraction ]      [ HELIUM-4  fraction ] ...
            [ NEON  fraction ]       [ XENON  fraction ] ...
            [ KRYPTON  fraction ]    [ METHANE   fraction ] ...
            [ ETHANE  fraction ]     [ ETHENE  fraction ] ...
            [ ACETYLENE  fraction ]  [ ISOBUTANE  fraction ] ...
            [ PROPANE  fraction ]    [ NEOPENTANE  fraction ] ...
            [ HYDROGEN  fraction ]   [ NITROGEN  fraction ] ...
            [ WATER  fraction ]      [ CO2  fraction ] ...
            [ CF4  fraction ]        [ OXYGEN  fraction ] ...
            [ DME  fraction ]        [ NITROUS-OXIDE  fraction ] ...
            [ AMMONIA  fraction ]
    
      Example:
    
      pressure {3*760}
      Heed argon 50 ethane 50
    
      (If you have a 3 atm 50/50 Argon-ethane mixture in your chamber.)
    

    INTERPOLATION

      The gas tables are usually interpolated with cubic splines.
      Sometimes splines oscillate too much and then you may prefer
      to use polynomial interpolation instead.
    
      Format:
    
      INTERPOLATION item1 method1 item2 method2 ...
    
      Examples:
    
      INTERP DRIFT-VELOCITY NEWTON 2,  LONG-DIFFUSION NEWTON 1
      INT TOWNSEND SPLINE
    

    Additional Information on:

  • item
  • method

  • MAGBOLTZ

      Invokes the Magboltz program to compute for electrons, the drift
      velocity, the longitudinal and transverse diffusion coefficients,
      the Townsend and attachment coefficients and the Lorentz angles
      if there is a magnetic field.
    
      Since Magboltz takes the magnetic field into account to compute the
      transport properties, the magnetic field section should precede the
      gas section.
    
      Likewise, the temperature and the pressure should be specified
      before issuing the MAGBOLTZ command. If the temperature is not
      specified before the MAGBOLTZ command, then a default temperature
      of 300 K will be used. No scaling for temperature is applied if
      a different temperature is later given. If the pressure is not
      specified before the MAGBOLTZ command, then a default pressure of
      760 Torr will be used. The transport properties will be scaled
      according to the simple scaling laws described in the manual if
      a different pressure is specified later on. It is not recommended
      to rely on these scaling laws.
    
      The author of Magboltz, Steve Biagi, should be contacted for
      further information about this program.
    
      Format:
    
      MAGBOLTZ [ ARGON  frac ]            [ HELIUM-3  frac ] ...
               [ HELIUM-4  frac ]         [ NEON  frac ] ...
               [ XENON  frac ]            [ KRYPTON  frac ] ...
               [ METHANE  frac ]          [ ETHANE  frac ] ...
               [ ETHENE  frac ]           [ ACETYLENE  frac ] ...
               [ NITROGEN-A  frac ]       [ NITROGEN-B  frac ] ...
               [ AMMONIA  frac ]          [ OXYGEN  frac ] ...
               [ ISOBUTANE  frac ]        [ WATER  frac ] ...
               [ CO2  frac ]              [ METHYLAL-HOT  frac ] ...
               [ METHYLAL-COLD  frac ]    [ PROPANE  frac ] ...
               [ NEOPENTANE frac ]        [ CF4  frac ] ...
               [ DME  frac ]              [ NITRIC-OXIDE  frac ] ...
               [ NITROUS-OXIDE  frac ] ...
    
               [ E/P-RANGE epmin epmax ]  [ N-E/P nep ] ...
               [ LINEAR-E/P-SCALE | LOGARITHMIC-E/P-SCALE ] ...
               [ ANGLE-RANGE amin amax ]  [ N-ANGLE nangle ] ...
               [ NOPLOT-DISTRIBUTION-FUNCTIONS | ...
                 PLOT-DISTRIBUTION-FUNCTIONS ] ...
    
               [ SECOND-ORDER-TERMS | FIRST-ORDER-TERMS | ORDERS n ] ...
               [ NOITERATE-ALPHA | ITERATE-ALPHA ] ...
               [ SWITCH [alpha/pressure] | NOSWITCH ] ...
               [ F0-TRANSVERSE-DIFFUSION | H1-TRANSVERSE-DIFFUSION | ...
                 MEAN-ENERGY-TRANSVERSE-DIFFUSION ] ...
               [ F0-LONGITUDINAL-DIFFUSION | H1-LONGITUDINAL-DIFFUSION | ...
                 G0-LONGITUDINAL-DIFFUSION ] ...
    
               [ MOBILITY mob ]
    
      Example:
    
      magboltz argon 50 ethane 50
    
      (The gas in your chamber will be 50 % Argon and 50 % Ethane.)
    

    Additional Information on:

  • frac
  • E/P-RANGE
  • N-E/P
  • scale
  • ANGLE-RANGE
  • N-ANGLE
  • PLOT-DISTRIBUTION-FUNCTIONS
  • ORDERS
  • SECOND-ORDER-TERMS
  • FIRST-ORDER-TERMS
  • ITERATE-ALPHA
  • SWITCH
  • DIFFUSION
  • MOBILITY

  • MIX

      Computes the drift velocity and diffusion for a mixture of
      gasses. The calculations are based on the work of G. Schultz
      and J. Gresser NIM 151 (1978) 413-431 and use parametrised
      cross section and energy loss data provided by Fabio Sauli
      and Anna Peisert.
    
      The main limitation of this method is that it neglects
      ionisation effects and that it treats excitation inaccurately.
      This implies that the results are not valid for large E/p
      values, i.e. close to the wires.
    
      Another limitation is that these calculations neglect the
      magnetic field - this is not an inherent limitation of the
      method, but there is no intention to invest further effort
      in this instruction. Garfield nowadays has an interface to
      the Magboltz program of Steve Biagi which is superior in
      accuracy to this instruction.
    
      Format:
    
      MIX [ ARGON  frac ]          [ HELIUM  frac ] ...
          [ METHANE  frac ]        [ ETHANE  frac ] ...
          [ NEON  frac ]           [ NITROGEN  frac ] ...
          [ ISOBUTANE  frac ]      [ XENON  frac ] ...
          [ CO2  frac ]            [ METHYLAL  frac ] ...
          [ KRYPTON  frac ]        [ AMMONIA  frac ] ...
    
          [ MINIMUM-ENERGY emin ] ...
          [ MAXIMUM-ENERGY emax ] ...
          [ STEPSIZE-ENERGY estep ] ...
    
          [ CRITICAL-F0-FRACTION frcrit ] ...
    
          [ RANGE epmin epmax ] ...
          [ N n ] ...
          [ LINEAR-E/P-SCALE | LOGARITHMIC-E/P-SCALE ] ...
    
          [ PLOT-F0 | NOPLOT-F0 ] ...
          [ PLOT-ENERGY-LOSS | NOPLOT-ENERGY-LOSS ] ...
          [ PLOT-CROSS-SECTION | NOPLOT-CROSS-SECTION ] ...
          [ PLOT-PATH | NOPLOT-PATH ] ...
    
          [ PRINT-TABLES | NOPRINT-TABLES ] ...
    
          [ MOBILITY mob ] ...
          [ TOWNSEND-COEFFICIENT alpha/p ] ...
          [ ATTACHMENT-COEFFICIENT beta/p ]
    
      Example:
    
      mix argon 50 ethane 50
    
      The gas in your chamber will be 50 % Argon and 50 % Ethane.
    

    Additional Information on:

  • frac
  • emin
  • emax
  • estep
  • frcrit
  • RANGE
  • n
  • scale
  • PLOT-F0
  • PLOT-ENERGY-LOSS
  • PLOT-CROSS-SECTION
  • PLOT-PATH
  • PRINT-TABLES
  • MOBILITY
  • TOWNSEND-COEFFICIENT
  • ATTACHMENT-COEFFICIENT

  • OPTIONS

      Enters global and local options. Only the local options are listed here.
    
      Format:
    
      OPTIONS [NOGAS-PLOT | GAS-PLOT] ...
              [NOGAS-PRINT | GAS-PRINT]
    
      Example:
    
      OPT NOG-PL G-PR
    

    Additional Information on:

  • GAS-PRINT
  • GAS-PLOT

  • PARAMETERS

      Various parameters of the gas, such as the number of clusters per
      cm, are entered with this command.
    
      Most of this data is only used for signal simulations and even then
      only if the no CLUSTER statement is used to enter the cluster size
      distribution.
    
      Format:
    
      PARAMETERS [A a] [Z z] [RHO density] [E-PAIR epair] ...
                 [E-MOST-PROBABLE emprob] ...
                 [MEAN mean_number_of_clusters] ...
                 [TRANSVERSE-ION-DIFFUSION sigma_T] ...
                 [LONGITUDINAL-ION-DIFFUSION sigma_L]
    
      As shown in the format description, several lines may be used
      altough a single line is perfectly acceptable as well.
    
      Example:
    
      PARA MEAN 20
    
      (This format could be used if you wish to compute arrival time
      spectra and enter the cluster size distribution with CLUSTER.)
    

    Additional Information on:

  • A
  • E-MOST-PROBABLE
  • E-PAIR
  • MEAN
  • RHO
  • Z
  • sigma

  • PLOT-OPTIONS

      Selects the plots to be made in response to the GAS-PLOT option,
      when leaving the gas section.
    
      The PLOT-OPTION command also controls the range of the vertical
      axes of these plots and these plots and lets you choose linear
      or logarithmic scales for both axes.
    
      Several plots may be modified in a single statement.
    
      Format:
    
      PLOT-OPTIONS [plot [options]] ...
    
      Example:
    
      plot-options drift lin-x log-y nodiff nocluster
    
      (Requests a linear E/p axis and a logarithmic drift velocity
      axis, the opposite of the default. The diffusion coefficients
      and the cluster size distribution are not plotted.)
    

    Additional Information on:

  • plot
  • options

  • PRESSURE

      Sets the pressure of the gas.
    
      The pressure is used by the gas mixing instructions (MIX and
      MAGBOLTZ) and also by HEED. Please be sure to specify the
      pressure before issuing these commands.
    
      If you specify the pressure after a mixing command, then the
      tables will be prepared for standard atmospheric pressure and
      the conversion to the pressure you specify will be done by
      relying on the simple scaling laws described under TABLE.
    
      Format:
    
      PRESSURE p [unit]
    
      Example:
    
      pressure 2 bar
    

    Additional Information on:

  • unit

  • RESET

      Performs a reset of all gas-data entered so far. This instruction
      is only available in interactive mode.
    
      Format:
    
      RESET
    

    TABLE

      Enters the gas tables. This instruction has a fairly complicated
      structure and it is advisable to refer to the manual for details.
    
      Each of the table entries (drift, mobility, angle, diff, townsend,
      attach) may either be listed in the tables following the TABLE line.
      or be given as a function of the symbolic parameter EP, which equals
      E/p in V/cm.Torr.
    
      The value of E/p must be entered in the table along with the
      corresponding value of a quantity that is tabulated (as opposed to
      entered as a function). The place of the E/p values should be
      indicated by 'E/P'.
    
      If E/p is tabulated, even if there are no other tabulated items,
      then the E/p values from the table are taken to evaluate those
      entries that are specified by a function. RANGE and N are in this case
      ignored. If on the other hand all entries are functions, then RANGE
      and N come into effect.
    
      Please note that those quantities that obey simple pressure scaling
      laws, have to be entered multiplied by the appropriate power of the
      pressure, see under 'scaling'.
    
      The order of the numbers in the tables should correspond with those
      in the TABLE line.
    
      Format:
    
      TABLE [E/P] ...
            [DRIFT-VELOCITY [drift]] ...
            [ION-MOBILITY [mobility]] ...
            [LORENTZ-ANGLE [angle]] ...
            [LONGITUDINAL-DIFFUSION-COEFFICIENT [diff]] ...
            [TRANSVERSE-DIFFUSION-COEFFICIENT [diff]] ...
            [TOWNSEND-COEFFICIENT [townsend]] ...
            [ATTACHMENT-COEFFICIENT [attach]] ...
            [DUMMY [dummy]] ...
            [RANGE epmin epmax] [N nmax]
    
      This line is followed by tables for those items that are not
      functions. The end of the table is signalled by a blank line.
    
      Example:
    
      TABLE  DRIFT=100*EP, DIFF, E/P
      0.3 0.1
      0.1 0.2
      0.1 0.5
      0.2 1.0
      0.3 2.0
    
      (The drift velocity is entered as the function 100*E/p which is
      evaluated at the E/p values listed in the second column. The
      longitudinal diffusion is listed in the first column. The ion
      mobility, the Lorentz angle and the Townsend and attachment
      coefficients are not specified.)
    

    Additional Information on:

  • units
  • scaling
  • dummy

  • RANGE

      The range in E/p to be covered by the table. This parameter
      is relevant only if E/p is not tabulated i.e. if there is no
      E/P keyword on the TABLE instruction line.
    
      [By default: 0.1 to 100 V/cm.Torr in 20 logarithmic steps.]
    

    Additional Information on:

  • N

  • TEMPERATURE

      Sets the temperature of the gas.
    
      This parameter is used by the gas mixing instructions (MIX and
      MAGBOLTZ) and by HEED. Please make sure the temperature, if
      different from room temperature, has been specified before
      these instructions are issued.
    
      The temperature is not needed if the transport properties and
      the clustering properties have been entered via tables.
    
      Garfield applies, if required, pressure scaling of the transport
      properties but does not apply temperature scaling laws.
    
      Format:
    
      TEMPERATURE t [unit]
    
      Example:
    
      TEMPERATURE 300 K
    
      For room temperature.
    

    Additional Information on:

  • unit

  • WRITE

      Writes a compact format gas dataset to be read by a GET instruction.
    
      The use of this instruction is strongly recommended when you compute
      the electron transport properties with Magboltz or with MIX, both of
      which consume a lot of CPU time. WRITE is not of interest if you enter
      the electron transport parameters of your gas description with a TABLE
      statement.
    
      The dataset contains initialisation information for Heed, which
      will automatically be performed when re-reading the file with GET.
    
      The format of the compact dataset is subject to modification and
      backwards compatibility is not guaranteed. Compact datasets that
      can no longer be read and that are of value, can however be sent
      to the author of Garfield for recovery.
    
      Files written with WRITE should in principle not be edited. These
      files are also not meant to be easily readable, use the GAS-PRINT
      option or procedures like DRIFT_VELOCITY to obtain legible tables.
    
      Writing takes place while the section is being left, not when the
      WRITE command is issued. The statement can appear at any place in
      the gas section.
    
      Format:
    
      WRITE   DATASET dsname [member]   [REMARK remark]
    
      Examples:
    
      WR DATA 'vaxgarf"garfield lasagna"::[garfield]gas.dat' REM "Test gas"
    
      (The keywords DATASET and REMARK are required in this example since
      the member is omitted. The single quotes are needed because of the
      double quotes in the remote login string and also because of the two
      colons.)
    

    Additional Information on:

  • dsname
  • member
  • remark

  • Keyword index. Formatted on 10/11/98.