Plasma Startup and Ramp-Up

Bringing the plasma from breakdown to the 9.66 MA operating point, and back down, is a controlled trajectory through stability limits — not a single state.

Getting to the operating point

The design point — 9.66 MA, the target pressure, Q_sci 3.076 — is a destination, not a starting condition. The plasma must be created from gas breakdown, its current ramped up, its density and heating raised, and its shape and profiles established, all along a trajectory that stays inside the stability limits at every intermediate state. The same is true in reverse for a controlled ramp-down.

For a spherical tokamak with a tight center column, startup is complicated by the limited room for a conventional inductive solenoid. Alternative and supplementary startup methods — using radio-frequency waves or careful field programming to initiate and build current — are part of the design, because the machine cannot always rely on a large central transformer to raise the full current.

Why the path matters

Instabilities can appear during ramps even when the final state is stable, and the current and pressure profiles established during startup set the initial bootstrap and q-profile for flat-top operation. A poorly chosen trajectory can seed a disruption or leave the plasma in a hard-to-control state. Designing startup and ramp scenarios that reach the operating point robustly is a design-and-simulation exercise linked to the control stack.

• The operating point is reached along a trajectory, not instantly
• Tight ST geometry constrains inductive startup
• The startup path sets the initial profiles for flat-top operation

This page describes a design-and-simulation study, not a built machine. Construction begins Q2 2027; first-of-a-kind first tritium is targeted near 2030. No hardware net-gain is claimed before FOAK.