Ambipolar Potential Electrode Interface

Biased electrodes and plug heating shape the electrostatic potential that plugs the tandem mirror; the interface senses and drives that potential.

Confinement by potential

In a tandem mirror, the central-cell ions are confined not only by the magnetic mirror but by an electrostatic ambipolar potential raised in the end plugs. Controlling that potential is as central to the burner as current control is to a tokamak. This interface reads the potential profile and drives it via plug heating and bias electrodes.

Sense and actuate

# ambipolar potential regulation (burner)
phi_z = estimate_potential(emissive_probes, endloss_analyzer)
u     = potential_ctrl(phi_z, phi_ref, twin)
plug_heat(u.P_ecrh)         # raise plug potential via hot electrons
bias_electrode(u.V_bias)    # trim end potential
# confinement depends on phi_conf = phi_plug - phi_center

The controlled quantity is the confining potential dip between plug and center, not an absolute voltage. Emissive probes and end-loss ion analyzers estimate the potential profile; plug heating (raising the hot-electron population) and bias electrodes are the actuators.

Coupling and gates

• Tightly coupled to plug density — density and potential are not independent.
• Subject to the same un-post-dictable 166–830× regime gate: the potential dynamics have no experimental precedent at this scale.
• Sense side timestamped by L2; setpoint by L3; actuation by L1.

Owner: L3 for the potential setpoint, L1 for heating/bias actuation. Because the mirror's confinement rests on holding this potential in an untested regime, the interface is documented with explicit uncertainty rather than an implied performance guarantee. Design-and-simulation specification; the burner is not built.