Neutral-Beam Injection

High-energy neutral atoms are fired into the plasma to fuel it, heat the ions, and build the sloshing-ion population that sustains the plugs.

Injecting energy as neutrals

Charged particles cannot cross a strong magnetic field from outside, so the beams are launched as fast neutral atoms. They penetrate the field freely, then ionize inside the plasma through charge exchange and impact ionization, depositing their energy and momentum where they stop. Neutral-beam injection is a mature technology used across the fusion field.

Three jobs in the burner

• Heating: fast ions slow down on the background plasma, raising ion temperature in the central cell and plugs
• Sustaining the plugs: angled beams build the sloshing-ion population that holds the plug potential
• Fueling: injected atoms add particles, complementing pellet and gas fueling

Aiming matters

In the plugs, beam angle is not incidental — it is the control that creates sloshing ions and shapes the ambipolar potential and thermal barrier. Beam energy sets penetration depth and the turning-point location. The design specifies distinct beam lines for central-cell heating and for plug potential control.

Beams also load the vacuum system: un-ionized fraction and re-neutralized particles must be pumped. The heating power the beams deliver is part of the recirculating power the machine must supply from its own converted output, which is why beam efficiency matters to the overall power balance.

Beam reliability and uptime therefore feed directly into plant availability, since the plugs cannot hold their potential without them. The design study treats the beam lines as continuously-operating utilities, not intermittent tools, and sizes their redundancy accordingly.