Add option to build grid for only a single region

hypnotoad/cases/tokamak.py

@@ -263,6 +263,12 @@ class TokamakEquilibrium(Equilibrium):
             doc="Reverse the sign of toroidal magnetic field Bt.",
             value_type=bool,
         ),
+        single_region=WithMeta(
+            None,
+            doc="Select only a single region of the equilibrium to mesh. Currently "
+            "this must be a divertor leg region.",
+            value_type=[NoneType, str],
+        ),
         start_at_upper_outer=WithMeta(
             False,
             doc=(
@@ -767,10 +773,23 @@ def inside_wall(point: Point2D):
             # Specifications for a double null (connected or disconnected)
             leg_regions, core_regions, segments, connections = self.describeDoubleNull()
 
-        # Create a new dictionary, which will contain all regions
-        # including core and legs
-        all_regions = leg_regions.copy()
-        all_regions.update(self.coreRegionToRegion(core_regions))
+        if self.user_options.single_region != None:
+            this_region_name = self.user_options.single_region
+            if this_region_name not in leg_regions:
+                raise ValueError(
+                    f"single_region option only supports leg regions so far. Region "
+                    f"{this_region_name} not found in leg_regions {leg_regions.keys()}."
+                )
+            # Select just the single region `this_region_name`
+            all_regions = {this_region_name: leg_regions[this_region_name]}
+
+            # Delete any connections, because we only have a single region
+            connections = []
+        else:
+            # Create a new dictionary, which will contain all regions
+            # including core and legs
+            all_regions = leg_regions.copy()
+            all_regions.update(self.coreRegionToRegion(core_regions))
 
         # Create the regions in an OrderedDict, assign to self.regions
         self.regions = self.createRegionObjects(all_regions, segments)
@@ -1635,7 +1654,10 @@ def createRegionObjects(self, all_regions, segments):
         # The region objects need to be sorted, so that the
         # BoutMesh generator can use jyseps indices to introduce branch cuts
 
-        if "inner_lower_divertor" in region_objects:
+        if self.user_options.single_region != None:
+            # Only a single region present
+            ordering = [self.user_options.single_region]
+        elif "inner_lower_divertor" in region_objects:
             if not self.user_options.start_at_upper_outer:
                 ordering = [
                     "inner_lower_divertor",

hypnotoad/core/mesh.py

@@ -930,7 +930,11 @@ def geometry2(self):
         self.dphidy = self.hy * self.Btxy / (self.Bpxy * self.Rxy)
 
     def capBpYlowXpoint(self):
-        if self.equilibriumRegion.xPointsAtStart[self.radialIndex] is not None:
+        if (
+            self.equilibriumRegion.xPointsAtStart[self.radialIndex] is not None
+            and self.equilibriumRegion.connections[self.radialIndex]["lower"]
+            is not None
+        ):
             # Choose a minumum Bp as the average of the two values of Bpxy.centre
             # nearest to the X-point
             Bp_min = min(
@@ -941,7 +945,11 @@ def capBpYlowXpoint(self):
                     self.Bpxy.ylow[i, 0] = Bp_min
                 else:
                     break
-        if self.equilibriumRegion.xPointsAtStart[self.radialIndex + 1] is not None:
+        if (
+            self.equilibriumRegion.xPointsAtStart[self.radialIndex + 1] is not None
+            and self.equilibriumRegion.connections[self.radialIndex + 1]["lower"]
+            is not None
+        ):
             # Choose a minumum Bp as the average of the two values of Bpxy.centre
             # nearest to the X-point
             Bp_min = min(
@@ -952,7 +960,11 @@ def capBpYlowXpoint(self):
                     self.Bpxy.ylow[-i - 1, 0] = Bp_min
                 else:
                     break
-        if self.equilibriumRegion.xPointsAtEnd[self.radialIndex] is not None:
+        if (
+            self.equilibriumRegion.xPointsAtEnd[self.radialIndex] is not None
+            and self.equilibriumRegion.connections[self.radialIndex]["upper"]
+            is not None
+        ):
             # Choose a minumum Bp as the average of the two values of Bpxy.centre
             # nearest to the X-point
             Bp_min = min(
@@ -963,7 +975,11 @@ def capBpYlowXpoint(self):
                     self.Bpxy.ylow[i, -1] = Bp_min
                 else:
                     break
-        if self.equilibriumRegion.xPointsAtEnd[self.radialIndex + 1] is not None:
+        if (
+            self.equilibriumRegion.xPointsAtEnd[self.radialIndex + 1] is not None
+            and self.equilibriumRegion.connections[self.radialIndex + 1]["upper"]
+            is not None
+        ):
             # Choose a minumum Bp as the average of the two values of Bpxy.centre
             # nearest to the X-point
             Bp_min = min(