CERN home page CERN home page Consult pages Consult pages Writeups at CERN Writeups at CERN Garfield pages Garfield pages Help Help &GAS &GAS This page This page Table of contents Keyword index

&GAS: TABLE


entries

The following transport properties can be entered with the TABLE command:

functions

Entries which are given in the form of a parametrisation, may depend on the following variables:

Variable Meaning Value, Unit
ANGLE_EB Angle between E and B degrees
B Magnetic field Tesla
BOLTZMANN Boltzmann constant 1.380658E-23 J/K
ECHARGE Electron charge 1.60217733E-19 C
EP E/p V/cm.Torr
P Pressure Torr
T Temperature K

The magnetic field related quantities, ANGLE_EB and B, are to be used only when there is a magnetic field.

Example:

See the FIT_EXPONENTIAL procedure.


scaling

The simple scaling laws used by Garfield to extrapolate to a different pressure are listed in the table below. When using MAGBOLTZ or MIX to compute the transport properties, you are strongly advised to have the transport properties computed at the relevant pressure and temperature, instead of relying on the scaling laws.

quantity scaling enter
drift velocity v vs E/p v
ion mobility mu vs E/p mu
diffusion coefficients sigma.sqrt(p) vs E/p sigma.sqrt(p)
Townsend coefficient alpha/p vs E/p alpha/p
Attachment coefficient beta/p vs E/p beta/p
Lorentz angles - angle

Example: the diffusion coefficient varies approximately with pressure according to the formula:

   sigma(p=p1)=sigma(p=p0)*sqrt(p0)/sqrt(p1)

hence sigma.sqrt(p) is approximately constant.


DUMMY

The DUMMY keyword can be used to comment out a column of the gas tables. For instance, if you have prepared a table in which both the transverse and longitudinal diffusion are present and wish to assess the effect of transverse diffusion, then you could do as in this example:

Assigning the transverse diffusion:

table e/p trans-diff long-diff
      1   0.1        0.1
      2   0.1        0.2
      3   0.1        0.3

Not assigning the transverse diffusion:

table e/p dummy long-diff
      1   0.1   0.1
      2   0.1   0.2
      3   0.1   0.3

Alternatively, you could have kept the original table followed by a RESET TRANS-DIFF command.


electric_field

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 the table is composed exclusively of computed entries. There is in that case no E/P keyword on the TABLE instruction line.

You may specify that you wish linearly or logarithmically spaced points, and you may also select the number of points.

[By default: 100 to 100000 V/cm in 20 logarithmic steps.]


angle

Sets the range of angles between E and B to be covered by the table or the angle between E and B for which the table is meant to be used.

Specifying such a range is valid only if there is a magnetic field.

Even though specifying an angle range is useful mainly if you have at least one computed table entry which depends on the angle, you may also specify the range for a tabulated table. Doing this forces the table to have room for B or angle dependent entries, which you can later add with the ADD command.

For defaults and further considerations, see the choice of ANGLE for the MAGBOLTZ command.


magnetic_field

Sets the range of magnetic field strengths to be covered by the table or the magnetic field strength for which the table is meant to be used.

Specifying such a range is valid only if there is a magnetic field.

Even though specifying an magnetic field is useful mainly if you have at least one computed table entry which depends on this field, you may also specify the range for a tabulated table. Doing this forces the table to have room for B or angle dependent entries, which you can later add with the ADD command.

For defaults and further considerations, see the choice of B-FIELD for the MAGBOLTZ command.


Go to the top level, to &GAS, to TABLE, to the topic index or to the table of contents.

Formatted on 0100-09-02 at 06:56.