Particle stream is disrupted when sim tab is not active

[jessegreenberg]

1. Create a state where many photons are animating.
2. Minimize the simulatoin browser tab
3. Return to the sim. It will look like this:

We suspect it is about how photons are created in the model from the intensity and photon rate model Properties. The model creates a certain mumber of Photons each step, that must be getting disrupted.