Measurements of DIII-D poloidal field by fiber-optic pulsed polarimetry
Bibliographic record
Abstract
A new technique for measuring the spatial and temporal structure of the poloidal field is presented, whereby the magnetic field causes the polarization of light traveling through an optical fiber to rotate via the Faraday effect by an amount proportional to the strength of the field oriented along the fiber. In fiber optic pulsed polarimetry, changes in the polarization of the backscatter light from the fiber are detected, thereby permitting measurement of the field as a function of position along the fiber. In this proof-of-principle experiment, specially prepared single-mode fibers with weak fiber Bragg gratings were installed in the poloidal direction on the outside of the thermal blanket on DIII-D. Light at 532 nm from a mode-locked Nd:YAG laser was injected into the optical fibers. The laser repetition rate was 895 kHz with a pulse length of <10 ps, resulting in ∼1 μs temporal resolution. A photodetector system measured the Stokes polarization components necessary to determine the amount of polarization rotation. For this experiment, bandwidth limitations of the detectors resulted in a spatial resolution of ≈2 cm. The measured temporal and spatial distributions of the poloidal field are consistent with inductive probe measurements and Elastodynamic Finite Integration Technique reconstructions of the spatial distribution. This demonstrates the ability of this technique to provide real-time detection of the temporal and spatial variations of the poloidal field. Besides revealing more detailed information about the plasma, this new diagnostic capability can also help in detecting instabilities in real time, thereby enabling enhanced machine protection.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".