Ion Collector Grids

The final electrodes catch decelerated ions at high potential; their transparency, cooling, and bias set how much energy is recovered versus lost as heat.

The last surface

After the traveling-wave and electrostatic stages have decelerated the ions, the residual charge must be caught somewhere. That job falls to the collector grids: biased electrode surfaces held at high potential that receive the slowed ions, delivering their charge to the circuit at that voltage. How much energy is recovered depends on how completely the ions were decelerated before they arrive and on how the grid is biased.

Transparency versus interception

A grid must be open enough to let the beam pass through the earlier stages, yet solid enough to catch ions at the end. Every ion that strikes a grid wire rather than passing through gives up its full residual energy as heat at that spot, both wasting the energy that could have been recovered as charge and creating a local hot spot. Grid transparency is therefore a direct efficiency and thermal parameter, treated on its own page.

Biasing and energy recovery

• A collector biased near the ion arrival energy recovers charge at high voltage — maximum energy per ion.
• Bias set too high reflects ions back; set too low collects them with wasted residual energy.
• Multiple grids at graded bias widen the range of arrival energies collected efficiently.

Cooling and materials

Even a well-tuned collector absorbs the un-recovered residual and secondary-particle heat, so grids are actively cooled and built from low-sputter refractory materials. The heat they do absorb is exactly the input the thermionic bottoming stage recovers. Suppressing electrons liberated on impact — secondary electrons that would otherwise carry current the wrong way — is a related design task covered next.