Periodic & Multi-Stage Electrostatic DEC

Stacking several retarding stages at graded voltages lets an electrostatic converter accept a band of ion energies instead of a single value.

Widening the accepted energy band

A single retarding stage recovers a narrow slice of the spectrum efficiently. The remedy is a periodic, multi-stage electrostatic converter: several collectors in series, each biased to a different voltage, so that low-energy ions are stopped at the first low-voltage collector and progressively higher-energy ions reach the higher-voltage stages. Each ion is collected near its own energy, so the energy is recovered at close to its full value across a band.

The staircase approximation

Multi-stage electrostatic DEC approximates a continuously matched field with a staircase of discrete voltages. More stages give a finer staircase and higher efficiency, but each stage adds a high-voltage collector, insulation, and complexity. There is a practical optimum in the number of stages, beyond which added complexity outweighs the efficiency gain.

Comparison with traveling-wave conversion

• Electrostatic staging sorts ions by energy, using fixed voltages.
• TWDEC sorts ions by phase and velocity, using a moving wave — better matched to a continuously spread spectrum.
• Electrostatic stages are simpler and produce DC directly; TWDEC handles spread better but needs RF and rectification.

Role in the train

The burner uses electrostatic collection primarily to catch residual ions after the traveling-wave stage and to provide a robust, RF-free backstop. Because it produces high-voltage DC directly, it also simplifies part of the power-electronics chain. Its chief limits — breakdown at high voltage and heating from intercepted ions — lead directly into the high-voltage-standoff and thermionic pages.