1
$\begingroup$

I was just wondering ..... enter image description here

In this Image of an ion thruster, when the positively charged particles pass through the grids, wouldn't they just bombard the negatively charged grid(a fraction of them). This means that there must be a constant adjustment to maintain the potential difference between the grids. Is this the reason for the high energy consumption of these engines (along with ionization..)?

Improve this question
$\endgroup$

2 Answers 2

Reset to default
0
$\begingroup$

A good high power ion thruster uses a lot of energy to accelerate ions to high energies.

The image does not include any power source, which is a serious problem if a person looking at the image wants to understand how ion thrusters work.

A simple ion thruster woks like this:

A small amount of energy is used to ionize a bunch of atoms, then a much larger amount of energy is used to move some of the electrons away from the plasma. Now the plasma is a positively charged plasma, from which positive ions tend to fly off. If there's some negative object nearby, it accelerates the approaching positive charges and decelerates the positive charges that are moving away, so the negative object does not really do anything to the ions that move past it, but it may prevent ions flying off into the opposite direction.

Improve this answer
$\endgroup$
4
  • $\begingroup$ but wouldn't the positive ions that provide momentum and leave the engine through the grids collide with the negatively charged grid and hence neutralize the charge on the negative grid? This means that there has to be a way to replenish the charges on the grids to maintain the potential difference? $\endgroup$
    – Chandrahas
    Commented Jan 29, 2017 at 7:42
  • $\begingroup$ No, because ion optics focus the ions to go through the holes. The magnets are the ion optics. Positive ions fly out, while electrons that where knocked out from the positive ions go to the positive grid, which makes the grid neutral, unless the positive charge is replenished. $\endgroup$
    – stuffu
    Commented Jan 29, 2017 at 11:49
  • $\begingroup$ Well this is what NASA's website says "The PPU converts the electrical power from a power source—usually solar cells or a nuclear heat source—into the voltages needed for the hollow cathodes to operate, to bias the grids,and to provide the currents needed to produce the ion beam." So we do need a voltage to maintain the potentials, right? $\endgroup$
    – Chandrahas
    Commented Jan 30, 2017 at 2:29
  • $\begingroup$ Ok. Some ions hit the negative grid. When an ion thruster is badly designed, many ions hit the negative grid. $\endgroup$
    – stuffu
    Commented Jan 30, 2017 at 13:19
0
$\begingroup$

You say "constant adjustment" as if you expect a motor with a PID controller to be spinning cat's fur on the grid to keep its charge ;P

The grid keeps it charge with 1.) a battery and 2.) by connecting both electron guns' filament to the positive grid. An electron gun is a special filament that when heated (by passing current through it) expels electrons.

As the gas ions are passing by the negative grid, the electrons are jumping off and neutralizing the gas as it exits. This is just part of the circuit under normal operating conditions - the Thevenin equivalent voltage of the circuit would be such that it's adequately charged at all times.

Energy consumed by the system is 1.) work done to accelerate the ions and 2.) the work done to heat the electron gun filament.

Here's the circuit:

ion thruster

Improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.