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Gasflow sources

Neutrals from gas inflow can be specified in 1D UFILES. These represent the ionized source [ions/second], thus neutrals escaping the plasma are entirely reflected back into the plasma. If no UFILE is provided, the gas inflow is assumed to be ZERO.

If NRCYOPT=2 charge exchange neutrals exiting the plasma are instead assumed to be 100% lost and the net ion source is reduced compared to the neutral source. If a global particle confinement time is specified in the namelist, an extra recycling source is introduced to satisfy the particle balance equation.

NLRCYC=F

If this option is selected, then gas flow UFILEs can be provided only as species specific (see Section on gas flow UFILES).

NLRCYC=T

In this case the gas flow from UFILEs PREGAS/EXTGAS represents the ion source summed over all isotopic species with atomic number matching the namelist variable XZRCYC. If only isotopes of hydrogen are present among the background species, then there is no need to define XZRCYC. The gas flow is distributed among thermal species according to GFRAC.

Note that GFRAC represents the relative fraction of each thermal species with respect to the total, thus the sum of all GFRAC values must equal unity.

If the background plasma contains thermal ions from species with different atomic number, then gas flows for the species not included in XZRCYC can be provided as species-specific UFILEs.

With the option NLRCYC=.T. UFILEs for the total recycling ion source, summed over isotopes with atomic number equal to XZRCYC must also be provided.

IMPORTANT: The gasflow ion source number is not simply related to the gas flow (atoms/sec) at a valve far away from the plasma. An analysis of neutral transport across the plasma scrape-off-layer plasma (which is not included in TRANSP) will be needed to convert valve data to an estimate of the main plasma total ion source rate.
Similarly, TRANSP cannot convert H_α measurements to main plasma recycling ion source rates. This analysis must be done offline.