4-ID POLAR¶
Polarization and magnetic-scattering beamline at APS. This page walks the operational core CORA models today across four stations. It is a reverse-engineered first cut, not yet a running model.
| Property | Value |
|---|---|
| Asset | 4-ID POLAR (root Asset, tier = Unit, parent_id = None) |
| Facility | APS (bound via facility_code = "aps", FacilityKind = Site) |
| Sector | Sector 4 (organizational grouping; not a registered Asset) |
| Status | First cut, reverse-engineered (operational core modelled; Raman station and the diffractometer Assembly deferred) |
| Sources | Undulator pair on the S04ID straight section |
| Control stack | APS EPICS (the same floor as 2-BM); device handles bound from the beamline's instrument repo, carried confirm |
First cut, and confirm-pending by intent
This scaffold was reverse-engineered from the beamline's own Bluesky instrument repo (BCDA-APS/polar-bits); the extraction is in research/aps-reverse-engineering/. Unlike the 7-BM and 32-ID design-phase scaffolds, it binds the real EPICS control handles, because POLAR is operational. Every value is still carried as confirm until 4-ID staff verify it: a PV read from the operator's config is strong evidence, not a CORA-owned fact. What CORA needs the team to confirm is on Open questions.
What makes 4-ID different¶
4-ID POLAR is CORA's first non-tomography APS deployment. It is unlike the 2-BM, 7-BM, and 32-ID imaging beamlines in three ways:
- Polarization control. Three diamond phase retarders set the X-ray polarization state, the capability POLAR is built around. CORA has no phase-retarder Family yet (a loose
PhaseRetarder). - Magnetic scattering. Superconducting sample magnets (2 T at 4-ID-B, a high-field magnet at 4-ID-H) and low-temperature sample environments drive resonant magnetic scattering. New device classes to CORA:
Magnet(loose) andTemperatureController(since graduated to a catalog Family presentingRegulator). - Diffraction. Huber diffractometers at 4-ID-G replace the tomography stage with a multi-circle goniometer and reciprocal-space (hklpy2) coordination, a shape CORA models as an Assembly, not yet built.
It runs across four lead-shielded stations: 4-ID-A (optics), and 4-ID-B, 4-ID-G, 4-ID-H (experiment).
Scope: what is and is not modelled¶
This cut earns its abstractions. It models the operational core read from the beamline config and defers the rest.
| Part | In this cut | Why |
|---|---|---|
Optics spine (4-ID-A) |
Yes | Undulators, phase retarders, VDCM monochromator, white-beam and mono slits |
Per-station optics (4-ID-B/G/H) |
Yes | KB mirrors, filters, transfocator, beam-position monitors |
Diffractometers (4-ID-G) |
Yes, as plain devices | Modelled with their circle axis maps; the reusable Assembly(Diffractometer) is designed but deferred (DIFF-1, see Model) |
| Sample environment | Yes | Magnets, temperature controllers, sample tables, pump-probe laser, bound to loose Families |
Raman station (4-ID-Raman) |
No | Its device config did not extract (a broken symlink in the source clone); scope and devices are TOPO-2 |
| Preamps / lock-in / high-pressure cell | No | Present in the config; deferred as peripheral (SAMPLE-2) |
The deferred parts and the reasons are recorded on Model.
The beamline¶
The systems CORA models today, along the beam:
- Source: the generated device walk, rendered from the descriptor: the undulator source, the phase retarders, the VDCM monochromator and its slits, the diamond window, toroidal and high-heat-load mirrors, the transfocator, and the per-station KB mirrors and filters.
- Sample: the 4-ID-G diffractometers, the polarization analyzer, and the magnet / temperature / table sample environment across the stations.
- Detector: the Eiger area detector, flag-view cameras, beam-position monitors, and scaler counters.
Cutting across them:
- Controls: the EPICS control stack; the device handles are bound from the beamline config and carried confirm.
The cross-cutting reference view is the Inventory: the planned Asset tree by parent_id, with Families and the values still pending confirmation. The Source page is generated from the beamline.yaml descriptor.
Techniques¶
Techniques: what the modelled part of 4-ID is designed to do, as intent. Each is a portable Catalog Method that an APS Practice would adapt. POLAR's techniques (diffraction, magnetic scattering, dichroism) are new to CORA's imaging-heritage catalog and render unlinked, carried pending.
Governance¶
Governance: who will act at 4-ID and the trust shape that gates their commands. People and agents are facility principals at the APS Site.
Model¶
Model: the developer's by-kind index into where each CORA aggregate's 4-ID content lives, the loose-Family graduation plan, and the record of what is deliberately deferred (the diffractometer Assembly, the Raman station, scenarios, Models).
Not yet documented¶
4-ID is not yet driven by CORA, so the operations runbook (procedures, recipes, cautions, enclosure permits) and the live experiment view are deliberately not written yet: a runbook for a beamline CORA does not yet drive would be invention, not record. They join as the deployment firms up. The 2-BM deployment shows the shape they will take.