Question     

Why does Spark3D showing inconsistent multipaction results when the same model is run multiple times with the exact same settings?

Answer     

Spark3D uses a small number of electrons to run the model to balance between speed and accuracy. At times, this default value of 300 electrons may not be enough to get consistent results in breakdown power even though it is fine for most single-carrier modes and in waveguide models where the parallel plate approximation applies.

The solution is to increase the number of initial electrons to a higher number, let's say 5000. This should produce results that are more consistent between runs. Note that there will still be some randomness to the results because of the formulation. The 300 electron number can be used to get a ballpark figure to establish a baseline, and then run with higher number of initial electrons to get consistent results.