The Photoionization node is used to model photoionization, which is critical in positive gas discharges at both atmospheric and high pressure. This node is available as a subfeature of the Gas feature when electrons and positive ions are solved.

Select Number of exponential terms, Element order and define other parameters required by the photoionization model. The default is using three terms and linear element to model photoionization in air. The new electrons and positive ions generated by photoionization are added by the feature.