450 kV Arc-Current Feedback High-Voltage Power Supply for Electron-Beam Deep-Penetration Welding

Deep-penetration electron-beam welding of 150–300 mm thick stainless steel and titanium components demands beam power stability better than ±0.7 % at 60–180 kW while penetration depth varies dynamically with keyhole plasma conductivity. Arc-current feedback supplies therefore regulate the 450 kV acceleration voltage directly from real-time beam current measurement to maintain constant power into highly variable load impedance.

The generator uses a 12-stage parallel-fed Cockcroft-Walton multiplier driven by a 28 kHz phase-locked resonant inverter with primary-side series linear regulation capable of ±180 V correction at 450 kV. Beam current is sensed via a non-inductive toroidal transformer around the beam path after the magnetic lens, digitized at 220 kS/s, and used as the primary feedback variable instead of voltage. A digital PI loop adjusts inverter drive within 42 µs to maintain beam current setpoint, automatically raising high voltage by 4–11 kV during keyhole collapse events to restore power delivery.

Voltage droop during maximum 400 mA beam current is limited to <0.58 % by distributed 8 µF oil-filled storage capacitors and active droop compensation that injects a pre-programmed 180 A current ramp during the first 180 µs of high-power demand. Overshoot after sudden load reduction is damped by a parallel linear sink that absorbs up to 28 kW transiently.

Plasma suppression in thick-section welds uses a programmed voltage boost of 6–14 kV for 80–220 ms immediately after focus ramp initiation, counteracting the increased plasma density that would otherwise defocus the beam and cause root spiking. The boost profile is learned from the previous 30 welds and refined automatically.

Filament emission is stabilized by a separate floating –5.8 kV grid supply that modulates extraction voltage in opposition to acceleration changes, maintaining constant perveance and focal spot size within ±32 µm across the full power envelope.

Arc handling limits stored energy to 21 J and collapses voltage in <6 µs via primary crowbar, with recovery ramp shaped to avoid re-ignition of vaporized metal plumes. These arc-current feedback systems routinely achieve penetration depth control within ±0.9 mm on 220 mm thick Ti-6Al-4V pressure vessels and porosity below 0.4 % in 180 mm Inconel 718 welds at travel speeds up to 18 mm/s.