Thomson Scattering Interface

A pulsed laser and spatially resolved collection give calibrated electron temperature and density profiles; the interface is timing- and calibration-critical.

What it measures

Thomson scattering fires a high-power laser through the plasma and measures the Doppler-broadened, Rayleigh-scattered light at multiple spatial points to recover electron temperature (T_e) and density (n_e) profiles. On the breeder these profiles anchor the twin's kinetic state; the interface manages laser firing, collection, and inversion.

Interface elements

• Actuate: laser trigger (timing to plasma phase), energy monitor.
• Sense: spatially resolved spectra per collection volume.
• Derive: T_e from spectral width, n_e from scattered intensity (Rayleigh-calibrated).

# per-point Thomson inversion
for pt in collection_volumes:
    spec   = acquire(pt, laser_shot)
    T_e[pt] = fit_spectral_width(spec)          # Doppler broadening
    n_e[pt] = scale(intensity(spec), rayleigh_cal[pt], E_laser)
profile = assemble(T_e, n_e, channel_map)       # to twin

Density accuracy depends on a Rayleigh calibration at known gas pressure; temperature depends on spectral-fit quality. The laser trigger must be timed and PTP-stamped so each profile is attributable to a known plasma instant. This is a burst diagnostic — it samples at the laser repetition rate, not continuously.

Owner and role

Owner: L2 for acquisition and timestamping; L3 for inversion and profile assembly. It is not on a fast control loop; instead it is a high-value anchor that calibrates and constrains faster proxies (interferometry) in the twin. Design-and-simulation specification, validated against the twin before hardware.