&GAS: TABLE

E/P

Indicates where the E/p values are located in the listing that follows the command. The keyword is not followed by a function.

This is an optional keyword. If the E/P keyword is not used, then all transport properties must be specified by means of functions.

ATTACHMENT-COEFFICIENT

If not followed by a function, the keyword indicates the location of the attachment coefficients for electrons in the listing that follows the command.

The attachment coefficients are computed from the function if the keyword is followed by a function. The coefficients should not be part of the listing in this case.

With a view to pressure scaling, one should in either case enter the attachment coefficients divided by the pressure. The quantity to be entered thus has the unit of 1/(cm.Torr).

Access to the data is provided with the ATTACHMENT procedure.

[Entering attachment coefficients is optional.]

If not followed by a function, the keyword indicates the location, in the listing that follows the command, of the component of the electron velocity parallel with the part of B that is transverse with respect to E.

This velocity component is computed from the function if the keyword is followed by a function. The velocity component should not be part of the listing in this case.

In either case, one should enter the velocity component in units of cm/\μsec.

This component should only be included in the table if a magnetic field has been defined. Although you do not have to enter this component if a magnetic field has been defined, you're strongly advised to do so if you dispose of the relevant data. If the component has not been entered, but is needed for a calculation, then the missing velocity components will be computed using the Lorentz angle, if available, otherwise from the Langevin equation.

Access to the data is provided with the VELOCITY_BTRANSVERSE procedure.

[Entering this component of the velocity is optional.]

DRIFT-VELOCITY

Enters the drift velocity. The precise quantity to be entered depends on the presence or not of a magnetic field:

In case a magnetic field is present:
If not followed by a function, the keyword indicates the location, in the listing that follows the command, of the component of the electron velocity parallel with E. If you do not enter both the component parallel with E\×B and the component parallel with the part of B that is transverse with respect to E, then you should enter here the norm of the drift velocity.
A function following this keyword should return the quantity described above. There should not be a corresponding item in the table if a function is specified.
In case there is no magnetic field:
If not followed by a function, the keyword indicates the location, in the listing that follows the command, of the norm of the electron drift velocity.
The velocity is computed from the function if the keyword is followed by a function. The velocity should not be part of the listing in this case.
The other components of the electron velocity vector should not be entered if there is no magnetic field.

In all cases, one should enter the velocity (component) in units of cm/\μsec.

The magnitude of the drift velocity can be accessed through the DRIFT_VELOCITY procedure. To obtain only the part parallel with E, one uses VELOCITY_E.

[Although entering the drift velocity is optional, one would normally do so since very few calculations can be performed if velocity data is absent.]

ExB-VELOCITY

If not followed by a function, the keyword indicates the location, in the listing that follows the command, of the component of the electron velocity parallel with E\×B.

This velocity component is computed from the function if the keyword is followed by a function. The velocity component should not be part of the listing in this case.

In either case, one should enter the velocity component in units of cm/\μsec.

Access to the data is provided with the VELOCITY_ExB procedure.

[Entering this component of the velocity is optional.]

ION-DISSOCIATION-COEFFICIENT

If not followed by a function, the keyword indicates the location of the dissociation coefficients for (negative) ions in the listing that follows the command.

The dissociation coefficients are computed from the function if the keyword is followed by a function. The coefficients should not be part of the listing in this case.

With a view to pressure scaling, one should in either case enter the dissociation coefficients divided by the pressure. The quantity to be entered thus has the unit of 1/(cm.Torr).

Access to the data is provided with the ION_DISSOCIATION procedure.

[Entering dissociation coefficients is optional.]

ION-MOBILITY

If not followed by a function, the keyword indicates the location, in the listing that follows the command, of the ion mobility.

The ion mobility is computed from the function if the keyword is followed by a function. The ion mobility should not be part of the listing in this case.

In either case, one should enter the ion mobility in units of cm\²/(\μsec.V).

Access to the data is provided with the ION_MOBILITY procedure.

[Entering the ion mobility is optional.]

LONGITUDINAL-DIFFUSION-COEFFICIENT

If not followed by a function, the keyword indicates the location, in the listing that follows the command, of the longitudinal diffusion coefficient for electrons.

The longitudinal diffusion coefficients are computed from the function if the keyword is followed by a function. The longitudinal diffusion coefficients should not be part of the listing in this case.

With a view to pressure scaling, one should in either case enter the amount of longitudinal diffusion over 1\ cm of drift, multiplied with the square root of the pressure. This quantity has the unit of \√(cm.Torr).

Access to the data is provided with the LONGITUDINAL_DIFFUSION procedure.

[Entering the longitudinal diffusion is optional.]

LORENTZ-ANGLE

If not followed by a function, the keyword indicates the location, in the listing that follows the command, of the Lorentz angle for electrons. This is the angle between the electric field and the drift velocity vector provided E and B are perpendicular.

The Lorentz angle is computed from the function if the keyword is followed by a function. The Lorentz angle should not be part of the listing in this case.

In either case, the Lorentz angle should be entered in degrees.

This component can only be included in the table if a magnetic field has been defined. If you have included all 3\ components of the drift velocity vector, then you do not have to enter the Lorentz angle since this information will not be used. If however you enter only the velocity component parallel with E, then you're strongly advised to tabulate the Lorentz angle if you dispose of the relevant data. If neither Lorentz angles nor transverse velocity components are available, then the velocity vector will be computed using the Langevin equation.

Access to the data is provided with the LORENTZ_ANGLE procedure.

[Entering Lorentz angles is is optional.]

TOWNSEND-COEFFICIENT

If not followed by a function, the keyword indicates the location of the Townsend coefficients for electrons in the listing that follows the command.

The Townsend coefficients are computed from the function if the keyword is followed by a function. The coefficients should not be part of the listing in this case.

With a view to pressure scaling, one should in either case enter the Townsend coefficient divided by the pressure. The quantity to be entered thus has the unit of 1/(cm.Torr).

Access to the data is provided with the TOWNSEND procedure.

[Entering Townsend coefficients is optional.]

TRANSVERSE-DIFFUSION-COEFFICIENT

If not followed by a function, the keyword indicates the location, in the listing that follows the command, of the transverse diffusion coefficient for electrons.

The transverse diffusion coefficients are computed from the function if the keyword is followed by a function. The transverse diffusion coefficients should not be part of the listing in this case.

The coordinate_system aligns the longitudinal diffusion with the electric field, not necessarily with the drift velocity vector. The transverse diffusion is the average of the diffusion perpendicular to E.

With a view to pressure scaling, one should in either case enter the amount of transverse diffusion over 1\ cm of drift, multiplied with the square root of the pressure. This quantity has the unit of \√(cm.Torr).

Access to the data is provided with the TRANSVERSE_DIFFUSION procedure.

[Entering the transverse diffusion is optional.]

function

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	1.380658 10\<SUP\>-23\</SUP\> J/K
`ECHARGE`	Electron charge	1.60217733 10\<SUP\>-19\</SUP\> 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	\μ vs E/p	\μ
diffusion coefficients	\σ.\√p vs E/p	\σ.\√p
Townsend coefficient	\α/p vs E/p	\α/p
Attachment coefficient	\η/p vs E/p	\η/p
Excitation rate	rate/p vs E/p	-
Lorentz angles	-	angle

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

\&sigma;(p=p1) = \&sigma;(p=p0) \&radic;p0/\&radic;p1

hence \σ.\√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.

E/P-RANGE

See electric_field.

N-E/P

See electric_field.

LOGARITHMIC-E/P-SCALE

See electric_field.

LINEAR-E/P-SCALE

See electric_field.

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-RANGE

See angle.

N-ANGLE

See angle.

ANGLE

See angle.

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.

B-RANGE

See magnetic_field.

N-B

See magnetic_field.

B-FIELD

See magnetic_field.

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.

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