Simple public API for user-defined pedestal pressure scaling

[theo-brown]

It would be useful to allow the user to specify a pedestal scaling without having to implement a new pedestal model.

For example, in STEP we have a model that gives $p_{e,ped}(n_{e,ped}, I_p, B_0, R_0, \delta)$ (based on power-law fits to Europed) and $\Delta_{ped}(\beta_{pol,ped})$ (modified EPED scaling). The exact form of this might be machine-specific.

Currently, implementing this model would require implementing a new pedestal model in the source code. We could copy the transport_model interface for public transport models to enable easier coupling of simple custom pedestal models.

[Aaryan-549]

Hello @theo-brown , I would like to be assigned this issue.

My plan is to implement a public API for user-defined pedestal scalings by mirroring the design pattern of the existing public transport_model interface, as suggested in the issue description.

My approach will be:

1. Analyze the transport_model API: I'll first examine how the public transport_model interface is structured, specifically its registration and how it's called by the main simulation loop.
2. Define the New Pedestal API: I will define a new, user-facing class or configuration object that allows users to pass in their own custom scaling functions (e.g., for $p_{e,ped}$ and $\Delta_{ped}$). This will be designed to be flexible enough to handle different functional forms, like the power-law fits mentioned.
3. Integrate with Core Code: I will then integrate this new API into the torax pedestal module and simulation workflow, allowing the simulator to dynamically call the user-provided functions.
4. Validate with an Example: I'll add unit tests and a clear example (similar to those for custom transport models) to validate the implementation and demonstrate how a user can couple their own pedestal model.

This approach will provide the needed flexibility for users to input their own models without requiring any changes to the core torax source. I'm ready to begin.

[Aaryan-549]

I have created PR #1717 to address this. This new pull request introduces the public API for custom pedestal models as discussed and should close this issue when merged. Please have a look.