Multigroup neutral model #185
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- Floor prevents CX turning off. problem for CX with density channel
- When the hot neutrals approach the cold neutral temperature, wall reflection no longer turns them into cold neutrals. Prevents hot neutrals from becoming colder than cold neutrals by the wall.
Apply limiter/upwinding to both X and Y advection
Seems to work better for neutral perpendicular diffusion than MC.
Take field (Nn, Pn, NVn) and Dnn separately; only upwind the field, and use cell face average values for Dnn. Also add neutral_conduction switch.
target settings used in SOL and PFR regions, rather than SOL and PFR settings.
Seems to help with smoothness of profiles
Same as anomalous_diffusion, obtain flows in X and Y for output when diagnose = true. Note: Only saves perpendicular flux, not parallel flux.
- For debugging purposes
- added setting for pressure floor. Added temporary debug flags for using floored Nn and Pn in DnnNn and DnnPn calculation (otherwise they could unbalance and lead to density loss - need more testing). There is a secondary floor which kicks in at zero gradient, this is now linked to the primary floor (but 2 orders of magnitude below).
- Allows you to bias the CX sources towards either atom1 or atom2 which is particularly useful for the hot neutral model
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The neutral fluid approximation breaks down in the core where the neutrals are so hot they are nearly collisionless.
We assume a single neutral distribution. This means that those hot neutrals have no choice but to conduct their heat (preheat) to the nearby cold SOL neutrals, even though in reality they would pass through and hit the wall. To mitigate this issue, we can impose a conduction heat flux limiter, but this traps the hot neutrals in the core and prevents them from heating the walls, while the cold neutral preheat is okay in the SOL but too low in the PFR.
A solution could be to have a new species called hot neutrals. Both cold and hot neutrals would have the same atomic reactions available, but cold neutrals are created only through puffing and thermal recycling, while hot neutrals are created only through charge exchange or fast recycling.
To do: