Why was circa 600 volts used for DAWN's ion propulsion?

Question

This answer estimates that the DAWN spacecraft's solar-electric propulsion accelerated about 3 milligrams of Xe⁺¹ per second, using roughly 1350 Watts of electrical power. I estimate that 3 mg/sec of Xe⁺¹ should be about 2.2 amps, so the acceleration potential might be in the ballpark of 600 volts.

Is the choice of voltages near 1 kilovolt the result of some optimization in kinematics? If so, can it be explained quantitatively with a simple mathematical model? Would say 200 or 2000 volts have both resulted in poorer use of the available

solar-electric power?
propellant?
time?

potentially helpful answer and there good information in this paper about DAWN's engine progenitor: Performance of the NSTAR ion propulsion system on the Deep Space One mission that may be helpful as well. — uhoh, Apr 15 '20 at 04:18
You might want to change your estimations to the actual numbers you found in the paper you linked: 1100V, 1.76A, 23.43sccm — asdfex, Apr 15 '20 at 10:21
@asdfex ya I've just used the results of the previous answer to make an estimate for DAWN, and the paper I mentioned in the comment is for NSTAR. — uhoh, Apr 15 '20 at 10:50
@asdfex If you'd like to assert that a voltage from a paper from 2000 about Deep Space 1 is the same as a voltage used on the DAWN spacecraft launched 7 years later, consider writing it up as part of an answer rather than trying to get me to assert it in a question? — uhoh, Apr 15 '20 at 11:36
With limited power high voltage means low current, low particle flow, and mass flow, and low thrust, unless you switch to a heavier particle. — user3528438, Apr 15 '20 at 19:50
@asdfex so far I've only found The Dawn spacecraft was propelled by three xenon ion thrusters derived from NSTAR technology used by the Deep Space 1 spacecraft The way this is written suggest to me that Dawn's engines are not necessarily exactly the same as the NSTAR engine used by DS-1 and operated in exactly the same way. — uhoh, Apr 17 '20 at 02:08
"The ion thrusters for Dawn are identical to the DSI flight thrusters.". Brophy et al. in The ion propulsion system for DAWN, 2013 — asdfex, Apr 17 '20 at 07:52
@asdfex okay I've found it, thanks! https://www.researchgate.net/publication/239923134_The_Ion_Propulsion_System_for_Dawn — uhoh, Apr 17 '20 at 10:24
Being a transit geek, I can't help noticing that 600v is commonly used for streetcars and subways, so perhaps there are many components that would be considered COTS, or it's just familiar tech. — stolenmoment, May 02 '20 at 12:12

Why was circa 600 volts used for DAWN's ion propulsion?

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