🔄 Add beta_poloidal_eps calculation and documentation for poloidal be…

…ta limit
ukaea · Dec 16, 2024 · b7fbabf · b7fbabf
1 parent a0cdf6b
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diff --git a/documentation/proc-pages/physics-models/plasma_beta/plasma_beta.md b/documentation/proc-pages/physics-models/plasma_beta/plasma_beta.md
@@ -156,6 +156,15 @@ the inverse aspect ratio and $\beta_p$ is the poloidal $\beta$, constraint equat
 turned on with iteration variable no. 8 (`fbeta`). The limiting value of $\epsilon\beta_p$ 
 is be set using input parameter `beta_poloidal_eps_max`.
 
+!!! note "Origin of the $\epsilon\beta_p$ limit"
+
+    High poloidal beta shots in TFTR were performed[^6] and it was found that as $\beta_p$, 
+    exceeds approximately 1.2 times the aspect ratio, a separatrix with 
+    an inside poloidal field null is observed to limit the outer boundary 
+    of the plasma. Since the curvature of TFTR’s applied vertical field 
+    is constant, the appearance of the poloidal field null corresponds to 
+    the equilibrium poloidal beta limit.
+
 --------------------
 
 ### Beta upper limit

diff --git a/process/physics.py b/process/physics.py
@@ -1588,6 +1588,10 @@ def physics(self):
             - physics_variables.beta_beam
         )
 
+        physics_variables.beta_poloidal_eps = (
+            physics_variables.beta_poloidal * physics_variables.eps
+        )
+
         physics_variables.beta_thermal_poloidal = (
             physics_variables.beta_thermal
             * (physics_variables.btot / physics_variables.bp) ** 2
@@ -3672,14 +3676,14 @@ def outplas(self):
 
         po.ovarrf(
             self.outfile,
-            "2nd stability physics_variables.beta : beta_p / (R/a)",
-            "(eps*beta_poloidal)",
-            physics_variables.eps * physics_variables.beta_poloidal,
+            "Poloidal beta and inverse aspect ratio",
+            "(beta_poloidal_eps)",
+            physics_variables.beta_poloidal_eps,
             "OP ",
         )
         po.ovarrf(
             self.outfile,
-            "2nd stability physics_variables.beta upper limit",
+            "Poloidal beta and inverse aspect ratio upper limit",
             "(beta_poloidal_eps_max)",
             physics_variables.beta_poloidal_eps_max,
         )

diff --git a/source/fortran/physics_variables.f90 b/source/fortran/physics_variables.f90
@@ -68,6 +68,9 @@ module physics_variables
   real(dp) :: beta_poloidal
   !! poloidal beta
 
+  real(dp) :: beta_poloidal_eps
+  !! Poloidal beta and inverse aspcet ratio product
+
   real(dp) :: beta_toroidal
   !! toroidal beta
 
@@ -948,6 +951,7 @@ subroutine init_physics_variables
     beta_limit_lower = 0.0D0
     beta_beam = 0.0D0
     beta_poloidal = 0.0D0
+    beta_poloidal_eps = 0.0D0
     beta_toroidal = 0.0D0
     beta_thermal = 0.0D0
     beta_thermal_poloidal = 0.0D0