Plasma Current Feedback

L1 regulates the breeder plasma current toward its 9.66 MA operating value, coordinating the central solenoid and PF system deterministically.

Current as the master parameter

Plasma current I_p sets the poloidal field, the confinement, and the stability margins; the breeder's operating point targets 9.66 MA. L1 regulates I_p by controlling the loop voltage the central solenoid and PF system impose, tracking a programmed current waveform through ramp-up, flat-top, and ramp-down.

The regulation

L1 measures I_p from Rogowski/flux magnetics and compares against the reference waveform. The error drives the solenoid current-ramp command; because the plasma is inductively coupled, the controller accounts for mutual inductances so a solenoid change produces the intended I_p change without disturbing position and shape more than necessary. The control math is a coordinated multi-coil law executed in fabric.

Coupling and decoupling

• I_p, position, and shape share the same coil system.
• The controller uses a decoupling matrix so each objective is addressable.
• Current ramp rate is limited to respect field and force constraints.
• Flat-top I_p held at 9.66 MA while shape and stability loops operate.

Decoupling matters: a naive solenoid change would move the plasma radially and distort the shape. L1 applies a transformation so current, radial position, and shape can be commanded semi-independently, then lets the individual loops trim the residual coupling. This keeps the 9.66 MA flat-top stable while δ = −0.30 is maintained.

Disruptions and the current

The stored energy in a 9.66 MA current is what makes a disruption consequential, so current control is tightly bound to disruption avoidance. A controlled ramp-down is one mitigation path; an uncontrolled current quench is the event the protection stack exists to prevent or soften. L1 therefore treats I_p regulation and disruption handling as one coordinated problem.