How does a pulsed plasma thruster work?

[Leo Liu]

I really can't get my head around the concept of pulsed plasma thruster. All I know now is that it utilizes $\vec F=q \dot {\vec r}\times \vec B$. Could someone explain the mechanism to me, please? Thanks!

 

[Baluncore]

What exactly do you not understand.
https://en.wikipedia.org/wiki/Pulsed_plasma_thruster

 

[DaveE]

View attachment 290680
I really can't get my head around the concept of pulsed plasma thruster. All I know now is that it utilizes $\vec F=q \dot {\vec r}\times \vec B$. Could someone explain the mechanism to me, please? Thanks!

A short, hand wavy, description:
When the arc forms, hopefully on the right side near the teflon, it creates the B field (out of the page). Then the moving electrons (up) experience the force you described $\vec F=q \dot {\vec r}\times \vec B$ (to the right). So that arc is propelled to the right and pushes a bunch of teflon bits out with it. The arc extinguishes when it's source discharges, and then the cycle repeats.

I like to think that the force is created to oppose a change in the magnetic flux. For a given current amount, the flux can be reduced by increasing the loop area, i.e. pushing the arc away.

This is also how rail guns work, if you want to look into those too.

 

[Leo Liu]

A short, hand wavy, description:
When the arc forms, hopefully on the right side near the teflon, it creates the B field (out of the page). Then the moving electrons (up) experience the force you described $\vec F=q \dot {\vec r}\times \vec B$ (to the right). So that arc is propelled to the right and pushes a bunch of teflon bits out with it. The arc extinguishes when it's source discharges, and then the cycle repeats.

I like to think that the force is created to oppose a change in the magnetic flux. For a given current amount, the flux can be reduced by increasing the loop area, i.e. pushing the arc away.

This is also how rail guns work, if you want to look into those too.

Thank you. I understand everything now but what sets the plasma in motion.

 

[Baluncore]

but what sets the plasma in motion.

The arc is initiated across the contaminated surface of the PTFE. There is no atmosphere. The arc forms a high temperature plasma of PTFE breakdown products.
To explain the initial ion velocity, consider that the ions used for propulsion can only travel away from the PTFE, and that is at their thermal velocity in the plasma.

 

[DaveE]

Thank you. I understand everything now but what sets the plasma in motion.

Also collisions with the outward moving electrons will push some of the plasma. The charged ions will also feel E and B field forces, like the electrons.