atomic generators do not have descriptor array
atomic generator does not have descriptor array
Atomic generators do not have a descriptor array.
An atomic generator does not have a descriptor array.
Both would be fine when you include the 'an", and as you note, it then becomes your own 'feel' and 'sense' of the language that determines which one you would use.
I am less sure about the "a" before 'descriptor': I take it that 'array' is some display, or array of lights or components or something. If 'descriptor array' is a function, the 'a' would not be used, as in 'descriptor array capability'.
(You might tend to use the second, single noun version if you were making a direct comparison with some other instrument:
With a fusion combustor, one can read the proportion of quasars directly from a digitial display, whereas an atomic generator does not have a readout-system.
(I have no idea what I'm saying in this sentence, but the grammar's good!)