Skip to content

MAST dB/dt source authority

validation/mast_dbdt_authority.py is the dB/dt source-quantity admission gate. It protects canonical dBdt_gauss_per_s from a source-quantity ambiguity in the centre-column poloidal Mirnov array. The gate measures metadata, geometry, finite coverage, and timebase facts, but never differentiates, filters, reduces, fills, or converts a source trace.

Why the old loop is unsafe

The historical replay candidate selects the first row, replaces non-finite values with zero, applies np.gradient(field, time) * 1e4, and then takes a per-bin peak magnitude. This is retained only as a compatibility recipe. It is not an authoritative physical binding because the source metadata conflicts:

  • the pinned FAIR-MAST profile maps five xmc/CC/MV/* channels into b_field_pol_probe_cc_field, declares units T, and applies a 2e-6 scale;
  • the live array label says Tesla/sec, while its top-level units remain T;
  • the MAST magnetic-diagnostics paper describes the relevant fast centre-column Bv-coil output as non-integrated; and
  • the acquired artefact does not preserve a declaration resolving whether its stored values represent magnetic field or its time derivative.

Treating a derivative source as field would differentiate twice. Treating a field source as an existing derivative would omit the derivative. Numeric smoothness, magnitude, a name containing field, or a label containing Tesla/sec cannot resolve that choice.

Primary sources:

Exclusive transform contract

A future source can clear the gate through exactly one branch:

Attested source quantity Required source units Only admissible transform
magnetic field T differentiate once in physical time, then multiply by 1e4 G/T
magnetic-field time derivative T/s do not differentiate; multiply by 1e4 G/T

The contract units must exactly match the observed array metadata. Its own schema, pinned mapping commit/file digest, and canonical JSON digest are recomputed, so a post-attestation mutation cannot silently change branch or mapping lineage. Neither branch is executed by the authority gate.

Additional admission requirements

Resolving the quantity alone is insufficient. The source must also attest:

  1. the ordered five source rows 201, 210, 220, 230, 240;
  2. the complete ordered geometry inventory 201…240, finite phi/r/z values, and exact source-to-geometry indices 0, 9, 19, 29, 39;
  3. the dimensional meaning of the mapping scale and its evidence digest;
  4. measured component, probe orientation, and sign convention;
  5. probe reduction, missing-data, and bad-channel policies;
  6. filter and edge policies with a positive cutoff below source Nyquist;
  7. calibration evidence and positive one-standard-deviation uncertainty;
  8. released, signed geometry with a creator commit and value digests; and
  9. the pinned primary-source citations and a self-consistent authority digest.

The source timebase must be finite, strictly increasing, and uniform. Existing non-finite samples remain blockers; the gate never changes them to zero.

Real two-shot result

Generation-pinned shots 30421 and 30424 contain five field rows with 382,601 and 398,201 samples respectively. Both have a measured period of approximately 2e-6 s, or 500 kHz, and every field row has one non-finite value at index zero. The source exposes three 40-element geometry arrays, but their metadata still uses the combined unit string SI, degrees, m, a development revision, and no creator commit. It preserves neither the mapping-scale declaration nor an authority contract.

Both shots therefore remain blocked on the metadata-unit/label conflict, missing scale semantics, non-finite first samples, unreleased geometry, absent geometry creator commit, and absent dB/dt authority contract. Canonical binding, training, scientific validation, facility prediction, and control admission all remain false.

The two deterministic reports are retained as non-public operational evidence. They are byte-identical with file SHA-256 8ae8c8e5c43b621995727f562d8097673910f3c9c8cc44bae720b6f790617a84 and payload digest 39c4d603e5275d6f1902d26f032dd870e7f319c936b9506b25c0e5e505604736.

Reproduction

Run only against a verified SourceObjectManifest-v2 root:

python -m validation.mast_dbdt_authority \
  --manifest /external/source-v4/source_object_manifest.json \
  --artifact-root /external/source-v4 \
  --shot-id 30421 --shot-id 30424 \
  --json-out /external/l2f12d-dbdt-authority.json

The output is exclusive-create, deterministic, and self-digested. It contains metadata, shapes, finite-sample positions, timebase measurements, blockers, and digests only; it contains no raw or derived magnetic trace.