How can a very small electrode gap reduce the space-charge effect?

In a thermionic power converter, the space-charge effect occurs when emitted electrons form a cloud of negative charge between the electrodes, where their mutual repulsion disrupts the flow of current to the collector.12

Reducing the electrode gap to the order of micrometres—typically between 0.025 and 0.038 mm—minimizes this effect by limiting the space available for the electron cloud to build up, thereby reducing the electrostatic resistance encountered by electrons as they travel from the emitter to the collector. While this approach effectively mitigates the space-charge limitation, such small spacings are difficult to manufacture, which has restricted the practical application of these vacuum-type converters.1