Staged Collector Grids

Ions arrive with a spread of energies; a series of grids at rising voltages collects each energy band near its own potential to keep conversion efficient.

One voltage cannot fit all ions

The exhaust ions do not share a single energy — they span a distribution. If a single collector voltage were used, ions far from that voltage would waste energy or fail to be collected. The fix is to stage the collector: several grids held at progressively higher potentials, so each ion is collected at the grid whose voltage most nearly matches its energy. This is the direct-conversion analog of matching a load to a source.

Sorting by energy

After the electron suppressor, ions decelerate as they climb through the grid stack. A low-energy ion runs out of momentum and is collected at an early, low-voltage grid; a high-energy ion presses on to a later, high-voltage grid. Because each ion gives up nearly all its energy at a matched potential, the aggregate conversion efficiency stays high across the spread.

Design trade-offs

• More stages track the energy spread more closely but add complexity
• Grid transparency must be high to avoid intercepting ions early
• Each stage feeds its collected current to power electronics at its own voltage
• Grid heating and secondary emission bound the stage count

Multi-stage direct converters were built and tested on mirror exhaust in the 1980s, reaching high efficiency on realistic ion spectra. In the burner the number and voltage of stages is set by the modeled exhaust distribution from the expander. The staged output is then combined and conditioned to grid-standard AC — the last step before the machine's electricity reaches the co-located load.