TWDEC RF Coupling & Power Extraction

The decelerating ions drive current in the electrode structure; extracting that as usable RF power is a matched-load problem.

From particle motion to terminal power

When a bunch of ions passes a set of electrodes and is decelerated, it induces image currents in those electrodes. That induced current, flowing into the external circuit, is the recovered power. The decelerator is therefore both a beam optic and an RF generator: the beam is the source, and the electrode array plus its external load is the tank circuit that collects the energy.

Matching the load

Maximum energy is drawn from the beam when the electrode circuit's impedance is matched to the effective beam impedance. Too light a load and the field is too weak to decelerate strongly; too heavy a load and the wave collapses and ions slip out of phase. The operating point is tuned so that the decelerating field is strong enough to milk the bunch but not so strong that it de-bunches or reflects particles.

Frequency and structure scale

The RF frequency is set by the ion transit time between electrodes and the desired bunch spacing. Higher frequency means finer electrode pitch and tighter bunching but greater sensitivity to velocity spread; lower frequency relaxes tolerances at the cost of a longer structure. The burner's TWDEC design chooses this balance for the D-3He proton velocity.

Rectification and conditioning

• The recovered signal is high-power RF, not DC — it must be rectified before it can join the DC bus.
• Rectifier and filter losses are part of the stage efficiency budget.
• The conditioned DC then feeds the inverter and grid interface shared with the rest of the train.

Because the beam itself is the RF source, TWDEC has no rotating parts and no working fluid — one more reason the burner train needs almost no water.