Thomson Scattering
Laser Thomson scattering gives the fabric local electron temperature and density along a line of sight, the backbone of the core pressure map.
The measurement
A high-power laser pulse scatters off plasma electrons; the scattered light's spectral broadening gives the local electron temperature and its intensity gives the local electron density. Because it is spatially localized at each collection volume, Thomson scattering provides true profiles rather than line integrals — the anchor for the breeder's core pressure map.
Into the fabric
- Each spatial channel is validated and calibrated independently, then placed on normalized flux via the reconstructed equilibrium.
- Density from Thomson cross-checks the line-integrated interferometry, and disagreement triggers a validation flag.
- Dropped channels are imputed over the sensor-topology graph so the profile stays continuous.
- Temperature and density feed the pressure map, the instantaneous Q cross-check, and training sets in the feature store.
Sampling and timing
Thomson is pulsed at the laser repetition rate rather than continuously, so its samples are timestamped precisely and interpolated in the twin between pulses using the faster ECE and interferometry channels. Precision timestamping (see PTP timestamping) keeps its samples phase-aligned with the continuous diagnostics.
Role on each machine
On the breeder, Thomson defines the temperature and density profiles that set performance and stability near the negative-triangularity edge. On the burner, localized density and temperature measurements in the central cell and near the plugs help characterize the confinement the ambipolar potential provides. The calibration and channel map are versioned per machine in the registry.