Fix #607: standardize beta_n unit string to dimensionless '1'

notebooks/mhd_equilibrium_analysis.ipynb

@@ -207,7 +207,7 @@
       "q95                           8.671 -            [linear interpolation]\n",
       "q_edge                        11.73 -            [profile endpoint]\n",
       "beta_t                     0.001274 -            [volume and pressure integration]\n",
-      "beta_n                       0.0702 % m T / MA   [derived]\n",
+      "beta_n                       0.0702 -            [derived]\n",
       "li_virial                    0.6876 -            [Lao virial closure]\n",
       "shafranov_shift              0.0284 m            [difference]\n",
       "magnetic_shear         129-point profile -            [finite differences]\n"
@@ -221,7 +221,7 @@
     "    (\"elongation\", 1.0, \"-\"), (\"triangularity_upper\", 1.0, \"-\"),\n",
     "    (\"triangularity_lower\", 1.0, \"-\"), (\"volume\", 1.0, \"m^3\"),\n",
     "    (\"cross_section_area\", 1.0, \"m^2\"), (\"q0\", 1.0, \"-\"), (\"q95\", 1.0, \"-\"),\n",
-    "    (\"q_edge\", 1.0, \"-\"), (\"beta_t\", 1.0, \"-\"), (\"beta_n\", 1.0, \"% m T / MA\"),\n",
+    "    (\"q_edge\", 1.0, \"-\"), (\"beta_t\", 1.0, \"-\"), (\"beta_n\", 1.0, \"-\"),\n",
     "    (\"li_virial\", 1.0, \"-\"), (\"shafranov_shift\", 1.0, \"m\"),\n",
     "    (\"magnetic_shear\", 1.0, \"-\"),\n",
     ")\n",

test/test_parametric_equilibrium.py

@@ -129,6 +129,9 @@ def test_global_descriptors_and_radial_coordinates_have_definitions():
     assert descriptors["volume"].value == pytest.approx(2 * np.pi**2 * 1.0 * 0.35 * 0.5, rel=2e-3)
     assert descriptors["thermal_energy"].available
     assert descriptors["beta_t"].available
+    assert descriptors["beta_n"].available
+    assert descriptors["beta_n"].unit == "1"
+    assert descriptors["beta_n"].quality.get("scaling_convention") == "% m T / MA"
     assert len(descriptors.rational_surfaces[1.5]) == 1
     radial = derive_radial_coordinates(eq)
     np.testing.assert_allclose(radial["psi_n"].value[[0, -1]], [0, 1])
@@ -576,3 +579,11 @@ def test_explicit_flux_tolerance_overrides_the_derived_window():
     strict = derive_boundary_representation(eq, flux_tolerance=0.0)
     assert strict.provenance.tolerances["xpoint_flux_psi_n"] == 0.0
     assert not strict.topology.is_diverted
+
+
+def test_unavailable_beta_n_has_dimensionless_unit():
+    eq = _analytic_equilibrium()
+    eq_no_p = EquilibriumData(**{**eq.__dict__, "pressure": None})
+    descriptors = derive_global_descriptors(eq_no_p)
+    assert not descriptors["beta_n"].available
+    assert descriptors["beta_n"].unit == "1"

vaft/process/_equilibrium_parametric.py

@@ -779,7 +779,12 @@ def derive_global_descriptors(
     centimetres apart.  The poloidal field is computed through the equilibrium's
     own declared COCOS and per-radian flag, so a wrongly declared convention
     propagates into every field-derived quantity here.  The magnetic shear is
-    taken against the poloidal radius.
+    taken against the poloidal radius.  The normalized beta follows the Troyon
+    convention ``beta_N = 100 * beta_t * a * |B_t0| / |I_p|`` (with ``a`` in
+    metres, ``B_t0`` in tesla, and ``I_p`` in megamperes); its published unit
+    is ``"1"`` (dimensionless) conforming to IMAS ``global_quantities.beta_normal``,
+    with the conventional ``% * m * T / MA`` scaling factor folded into the value
+    and recorded in the derivation quality metadata.
 
     Applicability
     -------------
@@ -790,9 +795,8 @@ def derive_global_descriptors(
     Every quantity degrades independently: a missing pressure profile costs the
     energies and the betas but not the geometry.  A failure inside the pressure
     integration is captured as a warning on the returned report rather than
-    raised.  The normalized beta carries a non-SI unit string where the rest of
-    the module is SI, tracked in #607.  The virial internal inductance is
-    ill-conditioned as its coefficient approaches one.
+    raised.  The virial internal inductance is ill-conditioned as its coefficient
+    approaches one.
 
     Provenance
     ----------
@@ -916,11 +920,15 @@ def derive_global_descriptors(
         values["beta_t"] = _derived(eq, beta_t, "1", "2*mu0*<p>/Bt0^2", "volume and pressure integration", ("pressure", "bt0"))
         if geometry and eq.ip not in (None, 0):
             beta_n = 100 * beta_t * values["minor_radius"].value * abs(eq.bt0) / (abs(eq.ip) / 1e6)
-            values["beta_n"] = _derived(eq, beta_n, "% m T / MA", "100*beta_t*a*abs(Bt0)/abs(Ip_MA)", "derived", ("beta_t", "minor_radius", "bt0", "ip"))
+            values["beta_n"] = _derived(
+                eq, beta_n, "1", "100*beta_t*a*abs(Bt0)/abs(Ip_MA)", "derived",
+                ("beta_t", "minor_radius", "bt0", "ip"),
+                {"scaling_convention": "% m T / MA"},
+            )
     if average_pressure is not None and bpa not in (None, 0):
         values["beta_p_boundary_average"] = _derived(eq, 2 * MU0 * average_pressure / bpa**2, "1", "2*mu0*<p>/<Bp>_boundary^2", "boundary-field average", ("pressure", "psi", "lcfs"))
     for name, definition in (("beta_t", "2*mu0*<p>/Bt0^2"), ("beta_n", "100*beta_t*a*abs(Bt0)/abs(Ip_MA)"), ("beta_p_boundary_average", "2*mu0*<p>/<Bp>_boundary^2")):
-        values.setdefault(name, _unavailable(eq, "1" if name != "beta_n" else "% m T / MA", definition, "required pressure, geometry, current, or magnetic field is unavailable"))
+        values.setdefault(name, _unavailable(eq, "1", definition, "required pressure, geometry, current, or magnetic field is unavailable"))
     for name in ("s1", "s2", "s3", "alpha"):
         values[name] = _derived(eq, virial[name], "1", f"Shafranov boundary integral {name}", "shafranov_integrals", ("psi", "lcfs")) if name in virial else _unavailable(eq, "1", f"Shafranov {name}", "valid grid, LCFS, and boundary poloidal field are required")
     values["li_virial"] = _derived(eq, virial["li"], "1", "[S1/2+S2/2*(1-RT/R0)-S3]/(alpha-1)", "Lao virial closure", ("psi", "f", "pressure", "lcfs")) if "li" in virial else _unavailable(eq, "1", "Lao virial internal inductance", "F, pressure, field grid, and a well-conditioned alpha are required")