How much voltage'd can a Van de Graaff generator reach on the Moon?

I mean...completely without air!

Electrostatic devices are collecting charges i.e. electrons on the small sphere and holes on the bigger sphere. Charges are creating electric field around them and has unit V/m, Volts per meter (in neutral particle or molecule, electric field from negatively charged particle is cancelled by positively charged particle).. How much charges you can extract from one sphere and move to second sphere depends on e.g. radius of sphere and its size and what it's made of (free electrons in metal). The biggest Van de Graaff generator was entire building, and scientists were working inside of it. These are the first missing parameters in your question.

On the Moon there will be freely striking it photons from the Sun during Moon day, and high-energetic cosmic rays from outer space. After hitting sphere by high enough energetic photon metal is emitting electron in photoelectric effect. And it would be accelerated toward positive sphere. The more photons, the more cosmic-rays will hit spheres, the faster discharge rate.

 

Edited January 17, 20197 yr by Sensei

Paschen’s law give the breakdown voltage as a function of pressure

https://en.m.wikipedia.org/wiki/Paschen's_law

Air ionization is a limit to the maximum possible Electric field. 

It seems to be around 3e6 Volt/m! 

Surely on the Moon this value's more high, it's important because 

the stored energy depends on the square of Voltage...

Photoelectic effect depends on the presence of light 

so it's not a problem, maybe it can be useful to discharge

it very slowly... 

Edited January 18, 20197 yr by harlock

12 hours ago, swansont said:

Paschen’s law give the breakdown voltage as a function of pressure

https://en.m.wikipedia.org/wiki/Paschen's_law

Oh man there's one I completely forgot about roflmao. Must have been over 20 years since I last seen this one referenced.

Lunar dust to consider.

Do expect to see electrostatic generators used in some fashion.