**It can't exist and this is why**

This organism would have to be unlike any that lives on Earth. First of all, if the organism was in our upper atmosphere it would be too protected from the cosmic rays for sustainable life. If it has DNA, it would have to be very protected in order to prevent defects and damage. We're talking some kind of synthetic space suit as it were. All life that we know of has some kind DNA so this is pretty much a given.

Another factor is the distance between organism and producer of the cosmic rays. Obviously the further, the more sparse and unreliable it would be as an energy source,  too close and it might get incinerated. Just like Earth, I suggest some kind of Goldilocks Zone where the conditions are 'just right'.

All this being said, I would assume the organism also needs some kind of respiratory system, and a way of excreting unwanted gases, because nothing can survive from nothing but charged particles. 

To conclude, I do not believe this is possible because the organism needs to be able to absorb harmful cosmic radiation with out being harmed. It also needs to be outside of a planets magnetosphere whilst still being able to diffuse with gases.