Why don't ion thrusters work within the atmosphere?

[yrjosmiel]

So I was reading about ion propulsion when I read this:

Ion thrust engines are practical only in the vacuum of space and cannot take vehicles through the atmosphere because ion engines do not work in the presence of ions outside the engine. Additionally, the engine's minuscule thrust cannot overcome any significant air resistance. Spacecraft rely on conventional chemical rockets to initially reach orbit.
-Wikipedia

I understand the fact that drag will be too powerful for the ion thruster to overcome. However, why does it matter when there are foreign ions? Does the magnetic field of the grids pull ions from the atmosphere, thus pulling the entire thing backwards?

 

[Lord Jestocost]

The Wikipedia sentence "...cannot take vehicles through the atmosphere because ion engines do not work in the presence of ions outside the engine..." is nonsense.

The pressure inside ion thruster chambers must generally be very low in order to i) effectively make a plasma in the chamber and to ii) effectively accelerate the generated ions to high speeds. When air at normal pressure would enter the chamber, the processes would break down.

 

[Rx7man]

I think a large part of it is that air creates an immense drag on the vessel.. In space there is virtually no drag, so even a small, steady force applied over long periods of time will make something achieve great velocities, while in air, you'd essentially never get yourself moving

 

[etudiant]

Drag is secondary to the problem that Lord Jestocost highlighted, the ion engine functions by accelerating ions electro statically. That requires a clear path for the ions to accelerate in. If air intrudes, the ions bounce off the air molecules instead and the acceleration is so diffused that thrust is lost.