Some problems of openPMD when simulate laser wakefield acceleration

[JBGuan]

I just started learning about plasma acceleration. When I was learning fbpic software recently, I wanted to take a look of the dephasing process and the transformation of acceleration energy with other parameters. I encountered many problems and hope to get your helps. I want to simulate the dephasing process of laser wakefield acceleration, so I increased the distance of interaction to 10000e-6, maybe which is not reasonable. But because of my faults, I set the wrong parameter of p_zmax = 2000.e-6. Here is the settings of simulation. Then I have several problems want to consult you.

1. The setting of p_zmax is 2000.e-6 m, the iteration about at 39500, but why there still exist the accelerate and dephasing process after 2000.e-6 m according to the following figure.
   
2. The parameter of energy is getting by ts1.get_energy_spread(iteration=iteration, species='electrons', select={'uz' : [0.05, None]}). The first numble of output is the energy, but why the energy is so low just about few MeV and Why there exist many NAN of energy?
3. How can I see the process of dephasing?
4. At 3000 iteration we can get the rho field and phase space figure, then, the maxium energy is about 11MeV at 33500 iteration, but when I plot the rho field and uz-z as the following figure, why there can not see the phase space？ 5.I know that lpa can use the down ramp density to inject the electrons, but why the dens_func is to increase density?