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&GAS: TABLE


units

The units to be used for the various quantities are:

Item Unit
Attachment coefficient 1/cm
Drift velocity cm/microsec
Ion mobility cm2/microsec.V
Longitudinal diffusion cm for 1 cm of drift
Lorentz angle degrees
Townsend coefficient 1/cm
Transverse diffusion cm for 1 cm of drift


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.


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.]


N

The number of points in the table, relevant only in the case that E/p is not present in the table, i.e. if E/P is absent from the command line.

[By default: 20 points covering E/p from 0.1 to 100 V/cm.Torr]


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Formatted on 0100-08-27 at 04:53.