Add PlasmaDensityLimit class and integrate into physics and stellarat… by chris-ashe · Pull Request #4093 · ukaea/PROCESS

chris-ashe · 2026-02-12T10:41:31Z

…or models

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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 · 2026-02-12T10:49:41Z

Codecov Report

❌ Patch coverage is 64.70588% with 36 lines in your changes missing coverage. Please review.
✅ Project coverage is 46.94%. Comparing base (bb358d5) to head (c8dcd34).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
process/models/physics/density_limit.py	65.62%	33 Missing ⚠️
process/models/physics/physics.py	50.00%	2 Missing ⚠️
process/main.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4093      +/-   ##
==========================================
+ Coverage   46.86%   46.94%   +0.07%     
==========================================
  Files         136      137       +1     
  Lines       29228    29319      +91     
==========================================
+ Hits        13698    13764      +66     
- Misses      15530    15555      +25

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timothy-nunn

Please fix conflicts before a review can be provided

…or models

… class

…class

…Limit class

… class

…ityLimit class

…Limit class

…imit class

timothy-nunn · 2026-02-25T11:04:51Z

documentation/source/physics-models/plasma_density.md

Several density limit models are available in PROCESS. These are
calculated in routine calculate_density_limit(), which is called by physics.

Needs to be updated to reflect the new class

I cannot see this

timothy-nunn · 2026-02-25T11:05:58Z

process/models/physics/physics.py

+    def calculate_density_limit(
+        self,
+        b_plasma_toroidal_on_axis: float,
+        i_density_limit: int,
+        p_plasma_separatrix_mw: float,
+        p_hcd_injected_total_mw: float,
+        plasma_current: float,
+        prn1: float,
+        qcyl: float,
+        q95: float,
+        rmajor: float,
+        rminor: float,
+        a_plasma_surface: float,
+        zeff: float,
+    ) -> tuple[np.ndarray, float]:
+        """
+        Calculate the density limit using various models.
+
+        Args:
+            b_plasma_toroidal_on_axis (float): Toroidal field on axis (T).
+            i_density_limit (int): Switch denoting which formula to enforce.
+            p_plasma_separatrix_mw (float): Power flowing to the edge plasma via charged particles (MW).
+            p_hcd_injected_total_mw (float): Power injected into the plasma (MW).
+            plasma_current (float): Plasma current (A).
+            prn1 (float): Edge density / average plasma density.
+            qcyl (float): Equivalent cylindrical safety factor (qstar).
+            q95 (float): Safety factor at 95% surface.
+            rmajor (float): Plasma major radius (m).
+            rminor (float): Plasma minor radius (m).
+            a_plasma_surface (float): Plasma surface area (m^2).
+            zeff (float): Plasma effective charge.
+
+        Returns:
+            Tuple[np.ndarray, float]: A tuple containing:
+                - nd_plasma_electron_max_array (np.ndarray): Average plasma density limit using seven different models (m^-3).
+                - nd_plasma_electrons_max (float): Enforced average plasma density limit (m^-3).
+
+        Raises:
+            ValueError: If i_density_limit is not between 1 and 7.
+
+        Notes:
+            This routine calculates several different formulae for the density limit and enforces the one chosen by the user.
+            For i_density_limit = 1-5, 8, we scale the sepatrix density limit output by the ratio of the separatrix to volume averaged density
+
+        References:
+            - AEA FUS 172: Physics Assessment for the European Reactor Study
+
+            - N.A. Uckan and ITER Physics Group, 'ITER Physics Design Guidelines: 1989
+
+            - M. Bernert et al., “The H-mode density limit in the full tungsten ASDEX Upgrade tokamak,”
+              vol. 57, no. 1, pp. 014038-014038, Nov. 2014, doi: https://doi.org/10.1088/0741-3335/57/1/014038. ‌
+        """
+
+        if i_density_limit < 1 or i_density_limit > 7:
+            raise ProcessValueError(
+                "Illegal value for i_density_limit", i_density_limit=i_density_limit
+            )
+
+        nd_plasma_electron_max_array = np.empty((8,))
+
+        # Power per unit area crossing the plasma edge
+        # (excludes radiation and neutrons)
+
+        p_perp = p_plasma_separatrix_mw / a_plasma_surface
+
+        # Old ASDEX density limit formula
+        # This applies to the density at the plasma edge, so must be scaled
+        # to give the density limit applying to the average plasma density.
+
+        nd_plasma_electron_max_array[0] = self.calculate_asdex_density_limit(
+            p_perp=p_perp,
+            b_plasma_toroidal_on_axis=b_plasma_toroidal_on_axis,
+            q95=q95,
+            rmajor=rmajor,
+            prn1=prn1,
+        )
+
+        # Borrass density limit model for ITER (I)
+        # This applies to the density at the plasma edge, so must be scaled
+        # to give the density limit applying to the average plasma density.
+        # Borrass et al, ITER-TN-PH-9-6 (1989)
+
+        nd_plasma_electron_max_array[1] = self.calculate_borrass_iter_i_density_limit(
+            p_perp=p_perp,
+            b_plasma_toroidal_on_axis=b_plasma_toroidal_on_axis,
+            q95=q95,
+            rmajor=rmajor,
+            prn1=prn1,
+        )
+
+        # Borrass density limit model for ITER (II)
+        # This applies to the density at the plasma edge, so must be scaled
+        # to give the density limit applying to the average plasma density.
+        # This formula is (almost) identical to that in the original routine
+        # denlim (now deleted).
+
+        nd_plasma_electron_max_array[2] = self.calculate_borrass_iter_ii_density_limit(
+            p_perp=p_perp,
+            b_plasma_toroidal_on_axis=b_plasma_toroidal_on_axis,
+            q95=q95,
+            rmajor=rmajor,
+            prn1=prn1,
+        )
+
+        # JET edge radiation density limit model
+        # This applies to the density at the plasma edge, so must be scaled
+        # to give the density limit applying to the average plasma density.
+        # qcyl=qstar here, but literature is not clear.
+
+        nd_plasma_electron_max_array[3] = (
+            self.calculate_jet_edge_radiation_density_limit(
+                zeff=zeff,
+                p_hcd_injected_total_mw=p_hcd_injected_total_mw,
+                prn1=prn1,
+                qcyl=qcyl,
+            )
+        )
+
+        # JET simplified density limit model
+        # This applies to the density at the plasma edge, so must be scaled
+        # to give the density limit applying to the average plasma density.
+
+        nd_plasma_electron_max_array[4] = self.calculate_jet_simple_density_limit(
+            b_plasma_toroidal_on_axis=b_plasma_toroidal_on_axis,
+            p_plasma_separatrix_mw=p_plasma_separatrix_mw,
+            rmajor=rmajor,
+            prn1=prn1,
+        )
+
+        # Hugill-Murakami M.q limit
+        # qcyl=qstar here, which is okay according to the literature
+
+        nd_plasma_electron_max_array[5] = self.calculate_hugill_murakami_density_limit(
+            b_plasma_toroidal_on_axis=b_plasma_toroidal_on_axis, rmajor=rmajor, qcyl=qcyl
+        )
+
+        # Greenwald limit
+
+        nd_plasma_electron_max_array[6] = self.calculate_greenwald_density_limit(
+            c_plasma=plasma_current, rminor=rminor
+        )
+
+        nd_plasma_electron_max_array[7] = self.calculate_asdex_new_density_limit(
+            p_hcd_injected_total_mw=p_hcd_injected_total_mw,
+            c_plasma=plasma_current,
+            q95=q95,
+            prn1=prn1,
+        )
+
+        # Enforce the chosen density limit
+
+        return nd_plasma_electron_max_array, nd_plasma_electron_max_array[
+            i_density_limit - 1
+        ]


Is this ever called by the code?

Its ran from self.density_limit.run() on line 2462

process/models/physics/physics.py

timothy-nunn · 2026-02-26T13:13:20Z

tests/unit/test_physics.py


    nd_plasma_electron_max_array, nd_plasma_electrons_max = (
-        physics.calculate_density_limit(
+        PlasmaDensityLimit().calculate_density_limit(


Suggested change

PlasmaDensityLimit().calculate_density_limit(

physics.density_limit.calculate_density_limit(

timothy-nunn · 2026-02-26T13:14:23Z

process/models/physics/density_limit.py

The documentation style for this file is out of date, please use the numpy style

Changed to numpy

chris-ashe added Physics Relating to the physics models Refactor labels Feb 12, 2026

chris-ashe force-pushed the create_density_limit_class branch from e2784ec to aa1518c Compare February 12, 2026 13:44

chris-ashe marked this pull request as ready for review February 12, 2026 14:11

chris-ashe requested a review from a team as a code owner February 12, 2026 14:11

timothy-nunn reviewed Feb 19, 2026

View reviewed changes

chris-ashe added 12 commits February 21, 2026 14:06

Add PlasmaDensityLimit class and integrate into physics and stellarat…

e7a9daf

…or models

Add method to calculate Greenwald density limit in PlasmaDensityLimit…

0c5a267

… class

Add ASDEX new density limit calculation method to PlasmaDensityLimit …

d426753

…class

Add Hugill-Murakami density limit calculation method to PlasmaDensity…

0cfbfe5

…Limit class

Add JET simple density limit calculation method to PlasmaDensityLimit…

92cde1e

… class

Add JET edge radiation density limit calculation method to PlasmaDens…

d0ae5f6

…ityLimit class

Add Borrass ITER II density limit calculation method to PlasmaDensity…

5cf25a5

…Limit class

Add Borrass ITER I density limit calculation method to PlasmaDensityL…

a4a0f59

…imit class

Add ASDEX density limit calculation method to PlasmaDensityLimit class

b45829b

Add DensityLimitModel class for electron density model types

6a0a831

Implement multiple density limit models in PlasmaDensityLimit class

ac04273

Refactor density limit output handling in Physics class

f9d01b2

chris-ashe force-pushed the create_density_limit_class branch from d46b934 to f9d01b2 Compare February 21, 2026 14:06

Post merge conflict rebase commit

a4f2d2d

chris-ashe force-pushed the create_density_limit_class branch from 98854e8 to a4f2d2d Compare February 21, 2026 14:24

chris-ashe requested a review from timothy-nunn February 21, 2026 14:55

timothy-nunn self-assigned this Feb 25, 2026

timothy-nunn requested changes Feb 25, 2026

View reviewed changes

Requested changes, create new density limit file in physics models

177a8c0

chris-ashe requested a review from timothy-nunn February 26, 2026 08:50

timothy-nunn requested changes Feb 26, 2026

View reviewed changes

chris-ashe added 2 commits February 26, 2026 13:15

Fix documentation: update routine name for density limit calculation

e25f4d9

Change to numpy docstring style

c8dcd34

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	PlasmaDensityLimit().calculate_density_limit(
	physics.density_limit.calculate_density_limit(

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chris-ashe commented Feb 12, 2026

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