🐛 Fix critical property assignment for CROCOSuperconductingTFCoil

[chris-ashe]

This pull request refactors how the critical current values for TF coil turn cables and CROCO strands are calculated and passed within the superconducting model. The main focus is to ensure that the critical current for the entire turn cable is separated from that of individual CROCO strands, improving clarity and correctness in the data flow.

Refactoring of critical current calculations:

• In superconducting.py, the assignment of c_tf_turn_cables_critical and cur_tf_turn_croco_strand_critical is separated, with the strand critical current now explicitly calculated as the turn cable critical current divided by N_CROCO_STRANDS_TURN.
• In the tf_croco_superconductor_properties function, the value passed for c_turn_cables_critical is changed from the strand critical current to the overall turn critical current, ensuring the correct value is used in downstream calculations.

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 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 49.97%. Comparing base (c7056b0) to head (84db504).

Files with missing lines	Patch %	Lines
process/models/tfcoil/superconducting.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4645      +/-   ##
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- Coverage   49.97%   49.97%   -0.01%     
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  Files         151      151              
  Lines       30270    30271       +1     
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  Hits        15128    15128              
- Misses      15142    15143       +1     

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[kj5248]

This change makes sense and matches equations elsewhere in file and my understanding. However not sure if using an equation and its inversion is necessary?

[kj5248]

Calculation is right however I have concerns over circular nature of calculation with other places in the file. I'll flag them.

[kj5248]

This is the inversion of the other equation, so I am much more confident the calculations are right.

However should the calculations not all happen in the same direction ie cur_tf_turn_croco_strand_critical = j_superconductor_critical * a_tf_croco_strand then cur_tf_turn_critical = cur_tf_turn_croco_strand_critical * N_CROCO_STRANDS_TURN and then just pass this information along.

Rather than passing along cur_tf_turn_critical and then having to use this to calculate cur_tf_turn_croco_strand_critical again? Didn't look deeply, these could just be separate paths?