InnerLayer.SLAYER - DOCS - 🌱 Describe chi_tor as the toroidal momentum diffusivity, not a heat diffusivity

src/InnerLayer/SLAYER/LayerInputs.jl

@@ -183,8 +183,10 @@ profiles, without an intermediate file round-trip.
   - `zeff`      -- effective charge (default `1.0`).
   - `chi_perp`  -- perpendicular heat diffusivity [m²/s]. Scalar or a
     callable of `psi` (default `1.0`).
-  - `chi_tor`   -- toroidal heat diffusivity [m²/s]. Scalar or a callable
-    of `psi` (default `1.0`).
+  - `chi_tor`   -- Fitzpatrick's χ_φ: anomalous perpendicular ion MOMENTUM
+    diffusivity `[m²/s]` (a viscosity entering the vorticity and parallel-flow
+    equations — not a heat diffusivity). Scalar or a callable of `psi`
+    (default `1.0`).
   - `dr_val`    -- resistive interchange index `D_R = E + F + H²`
     (Glasser-Greene-Johnson 1975) feeding the critical-Δ formulas
     (`:lar`, `:rfitzp`, `:toroidal`). When `nothing` (default), Julia

src/InnerLayer/SLAYER/LayerParameters.jl

@@ -29,7 +29,7 @@ de-normalization. The parametrization uses `P_perp`, `P_tor`, and
 | `c_beta`   | Compressibility √(β_local / (1 + β_local))                        |
 | `D_norm`   | (d_β/r_s) · S^(1/3) · √ι_e  (Fitzpatrick normalized scale)        |
 | `P_perp`   | Perpendicular Prandtl number τ_R / τ_⊥                            |
-| `P_tor`    | Toroidal-direction Prandtl number τ_R / τ_‖tor                    |
+| `P_tor`    | Momentum (magnetic) Prandtl number τ_R / τ_φ, τ_φ = r_s²/χ_φ      |
 | `Q_e`      | Normalized electron diamagnetic: −tauk · ω_*e                     |
 | `Q_i`      | Normalized ion diamagnetic:      −tauk · ω_*i                     |
 | `iota_e`   | Q_e / (Q_e − Q_i)                                                 |
@@ -210,7 +210,10 @@ parametrization (P_perp/P_tor/D_norm; the older magnetic/electron Prandtl
   - `R0`      -- major radius [m]
   - `mu_i`    -- ion mass in proton-mass units (e.g. 2.0 for D)
   - `zeff`    -- effective charge
-  - `chi_perp`, `chi_tor` -- perpendicular / toroidal heat diffusivity [m²/s]
+  - `chi_perp` -- perpendicular energy diffusivity χ⊥ [m²/s]
+  - `chi_tor`  -- Fitzpatrick's χ_φ, the anomalous perpendicular ion momentum
+    diffusivity `[m²/s]` (a viscosity, not heat: it enters the vorticity and parallel-flow
+    equations through P_φ = τ_R·χ_φ/r_s², Burgess et al. 2026 Table 1)
   - `m`, `n`  -- poloidal / toroidal mode numbers at the surface
   - `dr_val`, `dgeo_val` -- inputs for the critical-Δ formula
   - `dc_type` -- one of `:none`, `:lar`, `:rfitzp`, `:toroidal`

src/Tearing/Runner/Control.jl

@@ -34,10 +34,13 @@ constructor.
     callable of `psi` overrides it
   - `mu_i`     -- ion mass in proton-mass units (default 2.0 for D)
   - `zeff`     -- effective charge
-  - `chi_perp`, `chi_tor` -- fallback perpendicular / toroidal heat
-    diffusivity [m²/s], used only when the kinetic file carries no usable
-    `chi_e`/`chi_phi` profile (dataset absent or all-zero); otherwise the
-    file's χ⊥(ψ)/χ_φ(ψ) take precedence
+  - `chi_perp`, `chi_tor` -- fallback scalars [m²/s], used only when the
+    kinetic file carries no usable `chi_e`/`chi_phi` profile (dataset absent
+    or all-zero); otherwise the file's χ⊥(ψ)/χ_φ(ψ) take precedence.
+    `chi_perp` is the perpendicular ENERGY diffusivity χ⊥; `chi_tor` is
+    Fitzpatrick's χ_φ, the anomalous perpendicular ion MOMENTUM diffusivity
+    (a viscosity, not a heat diffusivity: it enters the vorticity and
+    parallel-flow equations through P_φ = τ_R·χ_φ/r_s², Burgess et al. 2026 Table 1)
   - `dr_val`, `dgeo_val`  -- critical-Δ formula inputs. `nothing` (default)
     auto-derives them from the equilibrium: `dr_val` from the resistive
     interchange index `D_R = E + F + H²` at each surface, `dgeo_val` from the