Heating Power Modulation
The total auxiliary heating power is the main lever on plasma temperature and stored energy, and it is modulated in real time to hit control targets.
Power as a control input
Auxiliary heating, from beams and radio-frequency systems, sets how much energy is added to the plasma per second. Because plasma stored energy responds to the balance of input power against losses, modulating heating power is the primary way to control temperature, stored energy, and the fusion reaction rate, which itself depends steeply on temperature.
Feedback on stored energy
A common loop measures plasma stored energy or a proxy such as the diamagnetic signal and adjusts heating power to hold a target. The controller must respect the plasma's energy confinement time, the natural timescale over which stored energy responds, so it does not chase noise. Feedforward from the planned scenario is added to the feedback trim for a faster, calmer response.
Constraints and sharing
Total power is bounded by hardware ratings and by plasma limits: too much power can push toward pressure-driven instabilities or excessive divertor heat flux. When several heating systems share the job, an arbitration layer allocates the requested power across sources, respecting each source's rating and preferred deposition, and honoring reserved allocations for stabilization tasks.
- Heating power sets temperature and reaction rate
- Feedback holds stored energy near a target
- Respect confinement time to avoid chasing noise
- Arbitrate power across sources within limits
Modulation for diagnostics
Deliberately modulating power, then watching how the plasma responds, is also a measurement technique: the phase and amplitude of the temperature response reveal transport properties. Control systems support clean square-wave or sinusoidal modulation for this purpose without disturbing the main scenario. In the Kronos breeder model, heating modulation sustains the operating point that yields a simulated Q of 3.424; the machine is a design and simulation case.
Power modulation ties the heating subsystems into the overall plasma control problem.