Can anyone walk me through Field Reverse Configurations?

Discuss how polywell fusion works; share theoretical questions and answers.

Moderators: tonybarry, MSimon

prestonbarrows
Posts: 77
Joined: Sat Aug 03, 2013 4:41 pm

Re: Can anyone walk me through Field Reverse Configurations?

Postby prestonbarrows » Wed Dec 17, 2014 9:34 pm

In my limited experience in this field, I have seen two general ways to form an FRC.

The first is basically 'in situ' in a stationary tube. You have a solenoid with three sections. You start with static fields in each section aligned in alternating directions. You then light a low density plasma with RF etc. This plasma 'locks in' the background b-field. The center of the three coils is then very rapidly pulsed with monster capacitors in the opposite direction from where it started (Now all three coils are running the same direction). From Faraday's law, the large dB/dT induces a loop of current in the plasma around the axis maintaining the 'frozen in' initial field (which in now in the reverse direction of the background applied field). You end up with a self-contained plasmoid surrounding a current loop inside the external solenoid field.

Making the solenoids cone shaped can impart longitudinal velocity.

FRC.png
FRC.png (100.13 KiB) Viewed 1920 times


The second is more of a 'gun'. A high voltage pulse is applied across a coaxial rod and tube. Current flows out radially producing B-fields encircling the electrode. JXB forces act to pull the current sheet down the rod. This is very similar to a Dense Plasma Focus to begin with. At the end of the rod, with the right geometry and background B-fields, the current sheet can be made to pinch off again form the self-contained current loop plasmoid. You can make two of these guns of opposite rotation collide and have the plasmoids merge.

In your picture the red lines are coil cross-sections. You can tell the slanted coils are powered in the opposite direction from the rest since the b-fields make cusps instead of all running down the axis. Presumably, at t=0, the slanted coils are flipped in polarity. The black field lines highlight the initial 'frozen in' background fields as the FRC forms. You can see later that the green field lines form a solenoid field where all coils are oriented in the same direction. The slanted coils impart velocity and the plasmoids travel towards each other to merge in the center. The central set of coils presumably will pulse when they join to provide further compression.

Like tokamaks, pretty much all FRC are pulsed devices relying in induction to start up. Everything is driven by big capacitor banks and is over within microseconds. Similarly, on paper, you could use neutral beam injection etc. to sustain one indefinitely but such things are far down the road and not much actual engineering validation has been done on that front to my knowledge.

asdfuogh
Posts: 77
Joined: Wed Jan 23, 2013 6:58 am
Location: California

Re: Can anyone walk me through Field Reverse Configurations?

Postby asdfuogh » Wed Dec 17, 2014 11:11 pm

For more info, the most recent review of FRCs

http://scitation.aip.org/content/aip/jo ... /1.3613680

(there is also one by Tuszewski from a longer time ago which is also very good).

Another way to form FRCs is via a rotating magnetic field to establish an electron current. Essentially, you rotate a magnetic field at the right frequency (faster than ions can respond, slow enough that electrons respond), and then you drag electrons to establish a current.

>pretty much all FRC are pulsed devices relying in induction to start up. Everything is driven by big capacitor banks and is over within microseconds

http://journals.aps.org/prl/abstract/10 ... 105.045003

Millisecond range, actually. Use that article as a starting point to find more.

prestonbarrows
Posts: 77
Joined: Sat Aug 03, 2013 4:41 pm

Re: Can anyone walk me through Field Reverse Configurations?

Postby prestonbarrows » Thu Dec 18, 2014 12:15 am

asdfuogh wrote:http://journals.aps.org/prl/abstract/10 ... 105.045003

Millisecond range, actually. Use that article as a starting point to find more.


Thanks for the link. Just to note, the pulsed formation/translation stage is 10's of microseconds while the lifetime of the combined FRC after the two toroids merge is into the few milliseconds. Good illustration on the right plot of how colliding toroids can greatly increase their lifetimes. These times are similar to the simulations pictured earlier.

Does anyone have experimental examples of neutral beams or other methods of pumping an FRC?

FRC shot.png
FRC shot.png (185.04 KiB) Viewed 1914 times

asdfuogh
Posts: 77
Joined: Wed Jan 23, 2013 6:58 am
Location: California

Re: Can anyone walk me through Field Reverse Configurations?

Postby asdfuogh » Thu Dec 18, 2014 12:21 am

>Just to note, the pulsed formation/translation stage is 10's of microseconds while the lifetime of the combined FRC after the two toroids merge is into the few milliseconds. These times are similar to the simulations pictured earlier.

Ah, thanks for clarifying, I thought you were saying the plasmas only last microseconds.

>Does anyone have experimental examples of neutral beams or other methods of pumping an FRC?

Hmm, besides Tri Alpha, I think there may be a group in Japan (Nihon U, if I remember correctly..) that works on FRC experiments. I can't remember if they are working on neutral beam injection or if they are working on FRC translation. There is also some university in Russia, but that one I know even less of. Most other FRC experiments are aimed at fueling tokamaks or doing some kind of helicity control for tokamaks so they probably won't have it.

mattman
Posts: 456
Joined: Tue May 27, 2008 11:14 pm

Re: Can anyone walk me through Field Reverse Configurations?

Postby mattman » Thu Dec 18, 2014 4:45 am

In summary:


Image


Let me know if you see any issues.


All I meant was that plasma moves straight through null points. Be they in polywells or FRC.

asdfuogh
Posts: 77
Joined: Wed Jan 23, 2013 6:58 am
Location: California

Re: Can anyone walk me through Field Reverse Configurations?

Postby asdfuogh » Thu Dec 18, 2014 5:59 am

>All I meant was that plasma moves straight through null points. Be they in polywells or FRC.

No. You meant to draw a comparison of stability between the two which would be illegitimate. The polywell is interesting enough on its own, and it'd be great to look at it for its own worth instead of dragging down other methods..

mattman
Posts: 456
Joined: Tue May 27, 2008 11:14 pm

Re: Can anyone walk me through Field Reverse Configurations?

Postby mattman » Mon Dec 22, 2014 4:23 pm

I apologize for the misunderstanding.

choff
Posts: 2348
Joined: Thu Nov 08, 2007 5:02 am
Location: Vancouver, Canada

Re: Can anyone walk me through Field Reverse Configurations?

Postby choff » Mon Dec 29, 2014 10:45 pm

Would it be fair to say that the FRC gets it's stability from being injected with momentum into the opposing field, otherwise if stationary the plasmoid would just flip over or get kicked out the one end.
CHoff

Skipjack
Posts: 5824
Joined: Sun Sep 28, 2008 2:29 pm

Re: Can anyone walk me through Field Reverse Configurations?

Postby Skipjack » Wed May 13, 2015 6:49 pm

Mattman, the simulation shows a system where two FRCs are colliding in the middle. This is what Helion is doing (the channel is run by David Kirtley and MSNW LLC) and I think that this method has a pretty good chance of success.


Return to “Theory”

Who is online

Users browsing this forum: No registered users and 1 guest