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
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.)
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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
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Enters the cluster-size distribution. You may choose between entering a parametrisation, listing of all probabilities and a mixture of the two formats.
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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
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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"
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
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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.)
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
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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.)
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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.
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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
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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.)
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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.)
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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
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Performs a reset of all gas-data entered so far. This instruction is only available in interactive mode. Format: RESET
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.)
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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.]
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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.
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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.)
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