Plasma containment approaches

[undefined]

I've been reading some about the ITER project, tokamaks, and other approaches to plasma containment. Why can't ion trapping approaches such as an orbitrap be used for fusion plasma containment?

 

[DEvens]

http://en.wikipedia.org/wiki/Orbitrap
http://en.wikipedia.org/wiki/Lawson_criterion

 

[undefined]

Yes, I have been to both of those pages. I do not, however, know how to apply the Lawson criterion to the orbitrap.

 

[undefined]

I guess I'm trying to figure out why (from what I can tell) there are no electrostatic fields employed in a tokamak when such fields are so useful in trapping ions. It seems that great trouble is taken to use only magnetic fields.

 

[mathman]

In order for fusion to take place the ions have to collide at high speed. Trapping ions wouldn't work.

 

[undefined]

Clearly confinement alone is insufficient. You also need temperature on the order of 10⁸K to generate high energy collisions (as you mention), plasma of high enough density that collisions occur frequently for a long enough time to have a good probability of some of them resulting in fusion. However I still don't understand why electrostatic fields wouldn't be very useful in containing the plasma at a decent density for long enough for fusion to commence. Clearly heating would need to be accomplished by some other means (not particularly relevant to my question).

 

[berkeman]

Clearly confinement alone is insufficient. You also need temperature on the order of 10⁸K to generate high energy collisions (as you mention), plasma of high enough density that collisions occur frequently for a long enough time to have a good probability of some of them resulting in fusion. However I still don't understand why electrostatic fields wouldn't be very useful in containing the plasma at a decent density for long enough for fusion to commence. Clearly heating would need to be accomplished by some other means (not particularly relevant to my question).

Does a plasma have a net charge?

 

[undefined]

Plasma consists of ions, which are all charged (and the basis for any confinement scheme). Fusion is only occurring between the nuclei, so if some electrons were lost, that wouldn't seem to be prohibitive. It seems clear to me that it wouldn't work to strip out all of the electrons simply because it would result in too much charge build-up. Wouldn't electron loss at some point naturally reach an equilibrium when the electrical potential of the plasma got high enough relative to the positive electrode?

 

[mfb]

Loosing too many electrons would still make the whole thing unstable. You cannot confine hot electrons and ions at the same time properly with electrostatic fields.