Fix PF electrical accounting for Ohmic heating

[grmtrkngtn]

Description

The PF electrical demand previously included only the power-supply loss associated with ohmic heating, while the ohmic power itself was still added to the plasma thermal balance. This caused the whole-plant power balance to gain an amount exactly equal to p_plasma_ohmic_mw.

The fix accounts for the full wall-plug power required to supply ohmic heating, while only the PF supply losses contribute to secondary heat.

See #4419

************************ Power balance for power plant *************************

IN
Fusion power (MW) (p_fusion_total_mw) 1.67020126538901764e+03 OP
Energy multiplication in blanket and shield (MW) (p_blkt_multiplication_mw) 2.47869045393520537e+02 OP
TOTAL (MW) (p_nuclear_total_mw) 1.91807031078253817e+03 OP

OUT
Net electric (MW) (p_plant_electric_net_mw) 3.50000000004303502e+02 OP
Heat rejected by main power conversion circuit (MW) (p_turbine_loss_mw) 1.36108730187131050e+03 OP
Heat rejected by other circuits (secondary heat) (MW) (p_plant_secondary_heat_mw) 2.06983008906924198e+02 OP
TOTAL (MW) (p_plant_out_mw) 1.91807031078253817e+03 OP
Power plant overall imbalance (MW) (p_plant_imbalance_mw) 0.00000000000000000e+00 OP

---

We can see the power imabalance is correct now

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.
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• I have added documentation for my change, if appropriate.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.73%. Comparing base (e2d0521) to head (02f11a1).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4664   +/-   ##
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  Coverage   49.73%   49.73%           
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  Files         151      151           
  Lines       30297    30297           
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  Hits        15069    15069           
  Misses      15228    15228           

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[ajpearcey]

I can be very misinformed, but why does electrical losses in the PF coil depend linearly on the plasma resistivity?

[grmtrkngtn]

This term is intended to represent the power-supply loss associated with transferring the ohmic heating power to the plasma, rather than a resistive loss in the PF coils themselves.

Since the plasma ohmic heating is

P_ohmic = V_loop * I_p = I_p^2 * R_plasma ​

and therefore depends on the plasma resistance, a fixed power-supply efficiency gives a loss

P_ohmic * (1/η_psu − 1)

The PF coil/busbar losses are accounted for separately in pfpowermw.