Glossary

This page fixes the coordinate, normalization, grid, and workflow terminology used by NTX. Equations and derivations are in Physics.

Coordinates And Geometry

psi : Toroidal magnetic-flux surface label. File-backed workflows retain the source convention and record the mapping used by the solver.

s : Normalized toroidal flux, commonly s = psi / psi_edge.

rho : Normalized radius rho = sqrt(s). Derivatives with respect to rho are not interchangeable with derivatives with respect to physical radius.

theta, zeta : Boozer poloidal and toroidal angles used by the local operator. Their Fourier sign and field-period conventions are part of the geometry-input contract.

xi : Pitch-angle coordinate xi = v_parallel / v, with -1 <= xi <= 1.

B_theta, B_zeta : Covariant Boozer components of the magnetic field.

B^theta, B^zeta : Contravariant Boozer components of the magnetic field.

J : Boozer-coordinate Jacobian mathcal J. The identity mathcal J B^2 = B_zeta + iota B_theta is an active physics gate.

Normalized Parameters

nu_hat : Monoenergetic collisionality entering the Lorentz pitch-angle-scattering operator. It is not a species-profile collision frequency until the documented profile mapping is applied.

epsi_hat : Normalized radial-electric-field parameter multiplying tangential E x B precession in the local equation.

D11, D31, D13, D33 : NTX monoenergetic transport coefficients for radial and parallel-flow source systems. These are normalized coefficients, not dimensional particle, heat, or current fluxes.

D33_spitzer : Parallel-conductivity reference coefficient in the retained collision model.

Resolution And Diagnostics

n_theta, n_zeta : Angular collocation counts on the flux surface. They must resolve retained Fourier harmonics and variable-coefficient products.

n_xi : Highest retained Legendre index plus the implementation’s documented mode convention. Always verify the exact convention in GridSpec when comparing inputs across codes.

angular oversampling : Ratio between angular collocation and the strict Nyquist floor of retained harmonics. NTX warns below the measured recommended ratio; research claims still require two successive refinements.

full-system residual : Residual of the assembled Legendre-space equations, including reconstructed eliminated modes and constraints.

Schur residual : Residual of the reduced linear system actually solved. It diagnoses the numerical solve but does not replace the full-system residual.

Onsager diagnostic : Reciprocity check between the cross coefficients under the documented source and normalization conventions.

Workflow Terms

prepared geometry : Geometry-dependent arrays and operator structure assembled once for repeated collisionality or electric-field solves.

compiled closure : Lowered and JIT-compiled callable bound to a prepared system and static shape. Changing shapes or static options may trigger recompilation.

downstream closure : Species, energy, and profile integration performed outside the local monoenergetic solve, including bootstrap-current workflows. A downstream result must not be described as a directly solved NTX coefficient.

physics gate : Quantitative acceptance rule anchored to a model identity, convergence study, or independent reference. Each promoted gate owns a script, test, artifact, threshold, and documentation entry.

stress diagnostic : Reproducible evidence used to expose a difficult regime without promoting a general accuracy claim.