♻️ Refactor CS coil stresses

[chris-ashe]

This pull request makes significant improvements to the documentation and data structures for the central solenoid (CS) in the engineering models, as well as updates the plotting and cost calculation code to support new geometry and stress parameters. The main focus is on clarifying and expanding the CS geometry and stress calculations, adding new physical variables, and ensuring these are reflected throughout the codebase and documentation.

Documentation and Model Improvements:

• Major expansion and clarification of the central solenoid (CS) geometry and stress calculation documentation, including new equations, definitions, and references.
• Addition of new physical variables and parameters to the CS and PF coil data structures, such as inner/outer radii, toroidal area, steel area, cable space area, various stress profiles, and operating temperature.

Plotting and Visualization Enhancements:

• Updates to CS coil structure and stress profile plots to include new parameters (e.g., toroidal area, hoop and radial stress profiles), and improved labeling and layout for clarity.

Cost Model Adjustments:

• Cost calculations for PF coils now use the new a_cs_cable_space variable instead of the old awpoh, ensuring consistency with the revised data structure.

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Documentation and Model Updates

• Expanded and clarified the CS geometry and stress calculation documentation, including new sections on turn geometry, bore/peak field calculations, and explicit equations for radial and hoop stresses with referenced literature.
• Added new variables to PFCoilData for inner/outer radius, upper/lower/middle z locations, toroidal area, steel area, cable space area, bore field, outer midplane field, and detailed stress profiles.
• Clarified and renamed variables in BuildData for better consistency (e.g., specifying "radial" thickness).
• Added temp_cs_superconductor_operating as a new input and data variable for CS operating temperature.

Plotting and Visualization

• Updated CS coil structure plots to display the new toroidal area and improved axis/label formatting for stress plots.
• Enhanced the main plot routine to include new subplots for radial and hoop stress profiles using the updated CSCoil and CsFatigue models.

Cost Model

• Updated cost calculations for PF coil conductor and superconductor to use the new a_cs_cable_space variable, replacing the deprecated awpoh.

Checklist

I confirm that I have completed the following checks:

• My changes follow the PROCESS style guide
• I have justified any large differences in the regression tests caused by this pull request in the comments.
• I have added new tests where appropriate for the changes I have made.
• If I have had to change any existing unit or integration tests, I have justified this change in the pull request comments.
• If I have made documentation changes, I have checked they render correctly.
• I have added documentation for my change, if appropriate.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 54.86381% with 116 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.86%. Comparing base (0d00ff1) to head (e06a93c).
⚠️ Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
process/models/pfcoil.py	54.40%	88 Missing ⚠️
process/core/io/plot/summary.py	12.50%	28 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4262      +/-   ##
==========================================
+ Coverage   48.79%   48.86%   +0.07%     
==========================================
  Files         151      151              
  Lines       29339    29474     +135     
==========================================
+ Hits        14315    14402      +87     
- Misses      15024    15072      +48     

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[Copilot]

Pull request overview

This PR refactors the Central Solenoid (CS) engineering model by introducing clearer CS geometry/turn-geometry data structures, expanding CS-related variables (geometry, stress, temperature), and updating outputs, plotting, and cost calculations to use the new fields.

Changes:

• Refactors CS geometry and EU-DEMO turn geometry routines to return dataclasses and propagates new CS geometry variables through the PF/CS model.
• Replaces legacy CS conductor+void area variable (awpoh) with a_cs_cable_space across models, costs, and tests; adds CS operating temperature input/variable.
• Extends CS plotting and documentation to cover new geometry and stress quantities (including radial/hoop stress profiles and toroidal area).

Reviewed changes

Copilot reviewed 9 out of 11 changed files in this pull request and generated 12 comments.

Show a summary per file

File	Description
tests/unit/models/test_pfcoil.py	Updates CS-related unit tests for new dataclass returns and updated CS stress/area APIs.
tests/unit/models/test_costs_1990.py	Updates cost-model tests to use a_cs_cable_space instead of awpoh.
process/models/pfcoil.py	Implements CS dataclasses, new CS stress/geometry fields, updated outputs, and adds CS stress plotting helpers.
process/models/costs/costs.py	Switches PF/CS cost calculations from awpoh to a_cs_cable_space.
process/data_structure/pfcoil_variables.py	Adds/renames CS data fields (geometry, areas, stress profiles, operating temperature).
process/data_structure/build_variables.py	Clarifies CS build-variable docstrings (radial thickness naming).
process/core/io/plot/summary.py	Updates summary plotting to include new CS stress subplots and CS toroidal area annotation.
process/core/input.py	Adds new input variable temp_cs_superconductor_operating.
documentation/source/eng-models/central-solenoid.md	Expands CS documentation with new geometry/stress sections and equations.

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[geograham]

A few minor things and worth looking through the copilot suggestions.

[timothy-nunn]

Please also rebase so the tests can run on the CI

[je-cook]

I've just applied a few suggestions to push this through slightly. hope thats ok

[clmould]

I'm happy now, will approve when Georgie has approved

[geograham]

Happy for this to go in once it is passing (var name mfile errors in regression tests at the moment).

[je-cook]

For the variables that are in this PR that are used in future PRs is not really ok.
This time it will go in but in future please isolate the PR more explicitly.

[clmould]

Regression changes justified, merging !