Neutral Transport

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TRANSP uses the FRANTIC neutral transport code to track the neutral population during a simulation. Three neutral sources are considered, a 'warm' source due to wall recycling, a 'cold' source due to gas injection and a volumetric source due to neutral beam halo and recombination. FRANTIC employs the following scheme for indexing the different neutral species:

• 1 : Species 1 warm neutral source.
• 2 : Species 1 volume neutral source.
• 3 : Species 1 cold neutral source.
• 4 : Species 2 warm neutral source.
• 5 : Species 2 volume neutral source.
• 6 : Species 2 cold neutral source.
• etc.

Where the ordering of the neutral species is the same as for the thermal ion species.

General Settings

NSOMOD=1: This selects the FRANTIC neutral transport model.

NZONES_FRANTIC: This selects the number of radial zones used by FRANTIC (Default 20).

RECYCB: This determines how the specified recycling source is divided into warm and cold recycled neutrals. A fraction RECYCB of the source are considered warm neutrals while a fraction ( 1 - RECYCB ) are treated as cold.

NLRECO: Set this flag .TRUE. to turn on the FRANTIC recombination volume neutral source.

Temperature Settings

The cold gasflow source temperature can be specified via a Ufile read in using trigraph TGF [eV]. In the absence of Ufile data, the cold neutral temperatures are specified using the namelist entries E0IN(i). These use the numbering scheme described above. Note that this ONLY WORKS FOR THE COLD NEUTRALS, i.e. indices 3, 6, 9 etc. The volume sources are fixed at the local ion species temperature. The warm species temperatures are governed using the MOD0ED switch:

• MOD0ED = 1 : (Default) Trigraph TRC can be used to specify a time dependent warm neutral recycling temperature Ufile which is then used for all species. If this is absent then the warm neutral temperature is set for all species using the value of the TIEDGE namelist input.
  NOTE : If time dependent Ufile data is provided, MOD0ED=1 is enforced.
• MOD0ED = 2 : A fraction TI0FRC of the central ion temperature is used for the warm neutral species.
• MOD0ED = 3 : The edge electron temperature is used where 'edge' means just outside the plasma boundary.
• MOD0ED = 4 : The edge ion temperature is used where 'edge' means just outside the plasma boundary.

FH0ESC: The fraction of escaping neutrals to return as "warm" recycling source neutrals when NRYCYOPT!=2. The remainder are returned cold. If NRYCYOPT=2 then escaping neutrals are considered lost and are not returned to the plasma.

Angular Velocity

The angular velocity of the neutral sources is controlled using the MOD0ED_OMEGA switch. When this is set to 1 then angular velocity Ufile data will be used if available. If not the species angular velcoities will be taken from the values of the OMEG0IN(i) variables. These set the angular velocity of the different neutral sources using the numbering scheme above (all of them, not just the cold neutrals). Ufile data can be input using trigraph ORC for the warm recycling source and OGF for the cold gas flow source [rad/s].

When MOD0ED_OMEGA is set equal to 2, a fraction OMEG0FRC (Default 1.0) of the edge ion angular velocity is used for the angular velocity of the neutral sources.

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