Plasma Startup Sequence
Bringing the burner to a burning D-3He plasma is a staged process: field, seed plasma, plug potential, heating, then fuel.
Order of operations
A tandem mirror cannot be switched on in one step. The confining potential depends on plasma already being present in the plugs, and the burn depends on the potential. Startup is therefore a bootstrap sequence that builds each condition on the last. The design study models this sequence to confirm there is a stable path from cold machine to steady burn.
The stages
- Energize magnets: ramp the REBCO coils to full field, including the 26.49 T plugs
- Seed plasma: create initial plasma in central cell and plugs
- Build plug potential: apply ECRH and angled beams to raise the ambipolar potential and form the thermal barrier
- Heat to temperature: drive ion and electron temperature toward the D-3He operating point
- Fuel the burn: feed D and 3He via pellets and gas until the burn is self-consistent
Why sequencing matters
If fuel is added before the potential is established, it leaks out the ends too fast. If heating is applied without the thermal barrier, plug electrons never reach the temperature the potential needs. Each stage must reach its target before the next begins, and the control system holds the machine at each checkpoint until diagnostics confirm it is ready.
Startup and the reverse shutdown are also where operational safety margins are set. Because the machine is linear with open ends, an off-normal event tends to dump plasma harmlessly into the expander rather than triggering a disruption, which simplifies the sequence relative to a tokamak.