Multipaction is an electron resonance effect that occurs when applied RF fields accelerate electrons that are in a vacuum and cause them to impact a surface. Depending on the energy of the impact, it releases one or more electrons into the vacuum, producing an avalanche effect, similar to what we see in lasers. Multipaction only occurs in a vacuum. In this module, you will be introduced to the multipaction feature using Ansys HFSS in Ansys Electronics Desktop to help you design and analyze a wide range of cutting-edge applications. A coaxial geometry is used as a course model to demonstrate this feature.