&GAS: PARAMETERS

A

The number of nucleons per gas molecule.

This parameter is used by (and mandatory for):

the SRIM clustering model;
the Landau model which is used to compute the cluster size distribution if you didn't enter such a distribution yourself with CLUSTER nor asked HEED to simulate the ionisation process.

E-MOST-PROBABLE

The most probable, not the mean, energy loss in eV per cm.

This parameter is used only to compute the cluster size distribution if you didn't enter such a distribution yourself with CLUSTER nor asked HEED to simulate the ionisation process.

You may also type MOST-PROBABLE-ENERGY-LOSS.

E-PAIR

The energy in eV needed to ionise a molecule.

This parameter is used only to compute the cluster size distribution if you didn't enter such a distribution yourself with CLUSTER nor asked HEED to simulate the ionisation process.

You may also type PAIR-CREATION-ENERGY.

This parameter is not used when clustering is performed according to the HEED model, but it is required for the EXPONENTIAL-SPACING and EQUAL-SPACING clustering models. In the latter 2 cases, the parameter is required even if a cluster size distribution has been entered with a CLUSTER statement.

You may also type N-MEAN.

[No default setting.]

RHO

The density of the gas in g/cm\³.

This parameter is used by:

the SRIM clustering model;
the simple Landau model which is used to compute the cluster size distribution if you didn't enter such a distribution yourself with CLUSTER nor asked HEED to simulate the ionisation process.

SRIM files contain a density estimate and, when reading such a file with the SRIM command in the gas section, the gas density will be overwritten. It is therefore advisable to issue the PARAMETERS command after the SRIM command if you know the gas density.

Z

The nuclear charge of the gas molecules.

This parameter is used by (and mandatory for):

the SRIM clustering model;
the Landau model which is used to compute the cluster size distribution if you didn't enter such a distribution yourself with CLUSTER nor asked HEED to simulate the ionisation process.

THERMAL

Requests thermal diffusion be applied when drifting ions. The thermal diffusion coefficients are computed using the expression:

         .------
        / 2 k\<SUB\>B\</SUB\> T
\&sigma; = \\  /  ------
     \\/    q\<SUB\>e\</SUB\> E

Where

k\<SUB\>B\</SUB\> = Boltzmann constant, 1.38... 10\<SUP\>-23\</SUP\> J/K,
T = temperature of the gas [K],
q\<SUB\>e\</SUB\> = charge of the electron, 1.6... 10\<SUP\>-19\</SUP\> C,
E = local electric field [V/cm]

[By default, the diffusion is set to 0.]

sigma

The transverse and longitudinal diffusion coefficients for ions of the type expected to be produced in your chamber, filled with the gas being entered.

These coefficients are used for Monte_Carlo drift-line integration of ion trajectories.

The diffusion coefficients should be expressed in cm of diffusion over 1\ cm of drift.

[Both diffusion coefficients default to 0.]

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