How do emitted electrons create an electric current in an external circuit?

In a thermionic power converter, an electric current is created in an external circuit through the following process:

• Emission: A "hot plate" electrode is heated to a temperature sufficient to overcome the electronic work function, causing electrons to be emitted from its surface into the space between the electrodes.12
• Collection: These emitted electrons, which possess kinetic energy, travel toward a second, cooler electrode known as the collector.1
• Circuit Completion: The two electrodes are interconnected by an external load (such as a resistor). When the electrons strike the collector, a portion of their energy is used to force a flow of current through this external circuit, effectively converting thermal energy directly into electrical energy.1

To maintain efficiency, the collector must be kept at a lower temperature, and the system must manage the space-charge effect—where the negative charges of the emitted electrons repel one another—often by using a gas or vapor to neutralize the space between the electrodes.1