Reject zero-thickness superconducting TF at input validation

process/core/init.py

@@ -287,6 +287,29 @@ def check_process(inputs, data):  # noqa: ARG001
             "Iteration variables 13 and 140 cannot be used simultaneously",
         )
 
+    # A superconducting TF coil must have a non-zero inboard thickness.
+    # dr_tf_inboard is only derived from the winding pack and case thicknesses
+    # when dr_tf_wp_with_insulation (ixc = 140) is an iteration variable (see
+    # Build.calculate_radial_build); with neither ixc = 13 nor ixc = 140 active
+    # it stays at its input value, and the default of 0 silently removes the
+    # TF coil from the radial build. Stellarators calculate dr_tf_inboard
+    # during the model run, so are excluded from this check.
+    if (
+        data.stellarator.istell == 0
+        and data.ife.ife == 0
+        and data.tfcoil.i_tf_sup == TFConductorModel.SUPERCONDUCTING
+        and not (data.numerics.ixc[: data.numerics.n_iteration_variables] == 13).any()
+        and not (data.numerics.ixc[: data.numerics.n_iteration_variables] == 140).any()
+        and data.build.dr_tf_inboard <= 0.0
+    ):
+        raise ProcessValidationError(
+            "dr_tf_inboard is not positive: the superconducting inboard TF coil"
+            " has no thickness. Set dr_tf_inboard (or use ixc = 13), or make"
+            " dr_tf_wp_with_insulation an iteration variable (ixc = 140) so that"
+            " dr_tf_inboard is derived from the winding pack and case thicknesses",
+            dr_tf_inboard=data.build.dr_tf_inboard,
+        )
+
     # Can't use c_tf_turn as iteration var, constraint or
     # input if i_tf_turns_integer == 1
     if (

tests/unit/core/test_init.py

@@ -0,0 +1,74 @@
+"""Unit tests for input sanity checks in process.core.init.check_process."""
+
+import pytest
+
+from process.core.exceptions import ProcessValidationError
+from process.core.init import check_process
+from process.core.model import DataStructure
+from process.models.tfcoil.base import TFConductorModel
+
+
+def _validation_error_message(data):
+    """Run check_process and return any validation error message.
+
+    Later, unrelated checks may still fire on an otherwise-default
+    DataStructure, so callers assert on the message content rather than
+    on whether an error was raised.
+    """
+    try:
+        check_process(None, data)
+    except ProcessValidationError as error:
+        return str(error)
+    return ""
+
+
+def test_zero_thickness_superconducting_tf_is_rejected():
+    """SC TF with dr_tf_inboard left at 0 and neither ixc=13 nor ixc=140
+    active must fail validation instead of silently building a machine
+    with no inboard TF coil.
+    """
+    data = DataStructure()
+    data.tfcoil.i_tf_sup = TFConductorModel.SUPERCONDUCTING
+    data.build.dr_tf_inboard = 0.0
+
+    with pytest.raises(ProcessValidationError, match="dr_tf_inboard"):
+        check_process(None, data)
+
+
+def test_explicit_tf_thickness_is_accepted():
+    data = DataStructure()
+    data.tfcoil.i_tf_sup = TFConductorModel.SUPERCONDUCTING
+    data.build.dr_tf_inboard = 0.5
+
+    assert "dr_tf_inboard" not in _validation_error_message(data)
+
+
+def test_wp_thickness_iteration_variable_is_accepted():
+    """With ixc = 140 active, dr_tf_inboard is derived in the build model,
+    so a zero input value is legitimate.
+    """
+    data = DataStructure()
+    data.tfcoil.i_tf_sup = TFConductorModel.SUPERCONDUCTING
+    data.build.dr_tf_inboard = 0.0
+    data.numerics.n_iteration_variables = 1
+    data.numerics.ixc[0] = 140
+
+    assert "dr_tf_inboard" not in _validation_error_message(data)
+
+
+def test_resistive_tf_is_not_checked():
+    data = DataStructure()
+    data.tfcoil.i_tf_sup = TFConductorModel.WATER_COOLED_COPPER
+    data.build.dr_tf_inboard = 0.0
+
+    assert "dr_tf_inboard" not in _validation_error_message(data)
+
+
+def test_stellarator_is_not_checked():
+    """Stellarators calculate dr_tf_inboard during the model run."""
+    data = DataStructure()
+    data.stellarator.istell = 1
+    data.tfcoil.i_tf_sup = TFConductorModel.SUPERCONDUCTING
+    data.build.dr_tf_inboard = 0.0
+
+    assert "dr_tf_inboard" not in _validation_error_message(data)

tests/unit/core/test_input.py

@@ -12,7 +12,12 @@
 
 @pytest.fixture
 def data_structure_obj():
-    return DataStructure()
+    data = DataStructure()
+    # These parser tests run init_process on minimal input snippets; give the
+    # scaffold a valid TF thickness so configuration validation (which rejects
+    # a zero-thickness superconducting TF) does not reject the scaffold.
+    data.build.dr_tf_inboard = 1.0
+    return data
 
 
 def _create_input_file(directory, content: str):