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Specify pressure and temperature (the default). Enter values for the Pressure and Temperature. The ideal gas law is then used to calculate the background number density.
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Specify number density and temperature. In this case, enter a value for the Background number density and the Temperature is then used to compute the background pressure, which is often needed during postprocessing.
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Lookup table. In this case, specify two columns of data, the first column should be the Reduced electric field (SI unit: V·m2, default unit: Td) and the second column the Townsend coefficient data (SI unit: m2). When this option is chosen, a Units section appears below where the preferred unit can be selected. This data can often be found online, or can be generated by solving the Boltzmann equation under the two–term approximation.
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Coefficients. This allows for specification of a Townsend coefficient prefactor and a Townsend coefficient exponential factor. In the literature, the Townsend coefficient prefactor is usually given in units of 1/(cm torr), whereas the requested unit is s2/kg. Both units correspond to the same physical quantity, so it is acceptable to enter, 7.79[1/(cm*torr)] for the prefactor, which is also the default. Similarly, for the exponential factor, the literature reports in units of V/(cm torr), whereas the requested unit is m2/(s A). Again, both units correspond to the same physical quantity, so the unit reported in the literature can be appended to the numeric values entered.
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User defined. In this case, enter a value or expression for the Townsend growth coefficient. The default is 1E-22[m^2], but it should typically be a function of the reduced electric field.
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