From 1849ca2186b988f6bd019e37d4ab111640fc4ce8 Mon Sep 17 00:00:00 2001
From: chris-ashe <christopher.ashe@ukaea.uk>
Date: Sun, 8 Feb 2026 22:19:08 +0000
Subject: [PATCH 1/3] Add average neutron flux variable for plasma surface

---
 process/data_structure/physics_variables.py | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/process/data_structure/physics_variables.py b/process/data_structure/physics_variables.py
index f2a9a4205..ce1e9c99f 100644
--- a/process/data_structure/physics_variables.py
+++ b/process/data_structure/physics_variables.py
@@ -1283,6 +1283,9 @@
 pflux_fw_neutron_mw: float = None
 """average neutron wall load (MW/m2)"""
 
+plfux_plasma_surface_neutron_avg_mw: float = None
+"""Average neutron flux at plasma surface (MW/m2)"""
+
 
 wtgpd: float = None
 """mass of fuel used per day (g)"""
@@ -1630,6 +1633,7 @@ def init_physics_variables():
         vs_plasma_res_ramp, \
         vs_plasma_total_required, \
         pflux_fw_neutron_mw, \
+        plfux_plasma_surface_neutron_avg_mw, \
         wtgpd, \
         a_plasma_poloidal, \
         n_charge_plasma_effective_vol_avg, \
@@ -1893,6 +1897,7 @@ def init_physics_variables():
     vs_plasma_res_ramp = 0.0
     vs_plasma_total_required = 0.0
     pflux_fw_neutron_mw = 0.0
+    plfux_plasma_surface_neutron_avg_mw = 0.0
     wtgpd = 0.0
     a_plasma_poloidal = 0.0
     n_charge_plasma_effective_vol_avg = 0.0

From 5d59c77165cd3dc5be8e49d67344b6506a7d85c0 Mon Sep 17 00:00:00 2001
From: chris-ashe <christopher.ashe@ukaea.uk>
Date: Sun, 8 Feb 2026 22:24:26 +0000
Subject: [PATCH 2/3] Add average neutron flux calculation for plasma surface

---
 process/physics.py | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/process/physics.py b/process/physics.py
index 0ceba4300..887559792 100644
--- a/process/physics.py
+++ b/process/physics.py
@@ -2494,6 +2494,10 @@ def physics(self):
             - physics_variables.p_plasma_rad_mw
         )
 
+        physics_variables.plfux_plasma_surface_neutron_avg_mw = (
+            physics_variables.p_neutron_total_mw / physics_variables.a_plasma_surface
+        )
+
         # KLUDGE: Ensure p_plasma_separatrix_mw is continuously positive (physical, rather than
         # negative potential power), as required by other models (e.g.
         # Physics.calculate_density_limit())
@@ -5646,6 +5650,14 @@ def outplas(self):
             physics_variables.pflux_fw_rad_mw,
             "OP ",
         )
+        po.ovarre(
+            self.outfile,
+            "Average neutron flux at plasma surface (MW/m^2)",
+            "(plfux_plasma_surface_neutron_avg_mw)",
+            physics_variables.plfux_plasma_surface_neutron_avg_mw,
+            "OP ",
+        )
+
         po.ovarre(
             self.outfile,
             "Peaking factor for radiation first-wall load",

From 43e060e377ee61cc9a092c0fc7528647ae0009c6 Mon Sep 17 00:00:00 2001
From: chris-ashe <christopher.ashe@ukaea.uk>
Date: Sun, 8 Feb 2026 22:29:55 +0000
Subject: [PATCH 3/3] Add average neutron flux display in plasma information
 plot

---
 process/io/plot_proc.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/process/io/plot_proc.py b/process/io/plot_proc.py
index 95a6f80ad..26d2a1e98 100644
--- a/process/io/plot_proc.py
+++ b/process/io/plot_proc.py
@@ -2870,12 +2870,13 @@ def plot_main_plasma_information(
     )
 
     textstr_neutron = (
-        f"$P_{{\\text{{n,total}}}}$ {mfile.get('p_neutron_total_mw', scan=scan):.2f} MW"
+        f"$P_{{\\text{{n,total}}}}$ {mfile.get('p_neutron_total_mw', scan=scan):.2f} MW \n"
+        f"$\\phi_{{\\text{{n,avg}}}}$ {mfile.get('plfux_plasma_surface_neutron_avg_mw', scan=scan):.3f} MW/m²"
     )
 
     axis.text(
         0.775,
-        0.85,
+        0.875,
         textstr_neutron,
         fontsize=9,
         verticalalignment="top",