Neutral Beam Alignment and Interlocks
A neutral beam carries megawatts in a narrow line; misalignment can strike a wall, so aiming and geometric interlocks are safety-critical.
The aiming problem
A beam is aimed to deposit power in a chosen plasma region and to hit its dedicated beam dump when no plasma is present. Small angular errors translate, over the injector's long throw, into large position errors at the vessel, so alignment is set mechanically during commissioning and verified before each campaign.
Geometric interlocks
Interlocks confirm that the beam path is clear before injection: fast shutters or the calorimeter are in the correct position, the drift-duct apertures are aligned, and the intended dump is in place. If the plasma is absent or too small to absorb the beam, injection is inhibited so full power lands on the dump rather than a wall tile.
Thermal monitoring
Beam-facing components, the neutralizer, residual-ion dump, calorimeter, and scraper apertures, are actively cooled and instrumented. Thermocouples and, where possible, infrared views flag any surface taking more heat than its design load, which signals a steering error or a shift in the plasma's absorption. A temperature excursion trips the beam.
- Fixed mechanical aim, verified per campaign
- Confirm clear path and correct dump before firing
- Inhibit injection without an adequate plasma target
- Trip on beam-facing-component over-temperature
Reionization and stray power
Neutrals can be re-ionized by background gas before reaching the plasma and then bent by the field onto unintended surfaces, so background pressure in the drift duct is monitored and pumped hard. Stray-field and duct thermal sensors catch this stray power. Alignment control thus links to vacuum control and plasma-facing-component monitoring.
In the Kronos design study these behaviours are modeled as generic injector safeguards; the machines themselves are simulated, not operating.