Can anyone walk me through Field Reverse Configurations?

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mattman
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Can anyone walk me through Field Reverse Configurations?

Postby mattman » Sun Nov 02, 2014 12:46 am

Hello All,

I am working on understanding Field Reverse Configurations. Anyone have a good explanation of their mechanism?

prestonbarrows
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Re: Can anyone walk me through Field Reverse Configurations?

Postby prestonbarrows » Sun Nov 02, 2014 2:54 am

FRCs are not really my area of expertise but I know a few people who do work on them; enough to have absorbed at least the basics.

The general idea is to have a large solenoid to set up an axial field. Now imagine putting a smaller solenoid coaxially inside the first and running current through it in the opposite direction. The fields between the walls of the two coils point in the same direction, while inside the smaller coil they point in opposite directions. You will find you end up with two distinct regions: a toroidal shape around the inner coil whose field lines are closed and do not ever intersect the outer coil, and a slightly distorted version of the original background axial field.

An FRC replaces the inner coil with a loop of plasma current to produce the same results. You end up with a self-confined plasmoid fully separated from the walls. The benefits are you get nice closed field lines akin to a tokamak or stellerator but don't need to build the complex coils. Linear systems are much simpler/cheaper to build and lend themselves to some of the more rose-tinted fusion applications like thrusters and direct energy conversion.

I believe FRC also has certain inherent stability benefits over other schemes.

Image

hanelyp
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Re: Can anyone walk me through Field Reverse Configurations?

Postby hanelyp » Mon Nov 03, 2014 1:32 am

An FRC has favorable field curvature. I'm not so sure about the plasma current flipping over or drifting off center.
The daylight is uncomfortably bright for eyes so long in the dark.

mattman
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Re: Can anyone walk me through Field Reverse Configurations?

Postby mattman » Wed Nov 05, 2014 3:14 am

Ok.

IF that is a stable structure... then there has to be published work where the stability is worked out mathematically.

The math is a good place to start the explanation.

I am going through TAE 2012 paper and I will find it.

asdfuogh
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Re: Can anyone walk me through Field Reverse Configurations?

Postby asdfuogh » Tue Dec 09, 2014 8:09 am

In order to understand their stability, you need to work from a kinetic approach. MHD would show the FRC to be unstable to tilt, kink, or some kind of rotational mode, if I remember correctly. However, the main underlying reason for their stability is thought to be due to the finite larmour radius effect, especially because there is a null point (or ring, actually) where ions are essentially unmagnetized and thus sample all sorts of wavelengths.

D Tibbets
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Re: Can anyone walk me through Field Reverse Configurations?

Postby D Tibbets » Tue Dec 09, 2014 8:44 pm

My understanding of FRC is not exactly profound. But some Google research yielded these meager results. The third link is to a video. It is somewhat poor quality, but is interesting, especially the Q&A portion. It is significant perhaps that their research survived due to piggybacking on the Tokamak bandwagon. Using a FRC injector may be useful in a tokamak. It may also prove useful for a Polywell plasma injection tool. There are a lot of interactions in the fusion smorgasbord. Your project may not give the answer, but be a piece of the answer. Another reason that putting all your money into tokamaks is foolish.

http://fusionenergy.lanl.gov/Documents/ ... l%2099.pdf

http://depts.washington.edu/rppl/presen ... milroy.pdf

http://wn.com/field-reversed_configuration

Dan Tibbets
To error is human... and I'm very human.

asdfuogh
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Re: Can anyone walk me through Field Reverse Configurations?

Postby asdfuogh » Tue Dec 09, 2014 10:23 pm

>It is significant perhaps that their research survived due to piggybacking on the Tokamak bandwagon.

Most forms of fusion research survived through tokamak piggybacking (ie. FRCs for helicity control and injection, mirrors for pre-heating). However, it should be known that FRCs have the most attention in private investors, either for pulsed machines or steady-state machines. Polywell attention is incomparable, to be honest.

mattman
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Re: Can anyone walk me through Field Reverse Configurations?

Postby mattman » Sat Dec 13, 2014 4:13 pm

Dan,

Those slides are pretty good. The talk is terrible (skip to 23 minutes for FRC). I am reading

https://drive.google.com/file/d/0B8t9BSGalBr4ZG8wY09kbGI3c3c/view?usp=sharing

https://drive.google.com/file/d/0B8t9BSGalBr4X0JSa3paZWVRSzA/view?usp=sharing

So this is what this configuration looks like:

Image


1. How is this stable? What makes it unstable?

2. How do we measure the plasma actually doing this?

3. What are the biggest road blocks to making this commercial?

mattman
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Re: Can anyone walk me through Field Reverse Configurations?

Postby mattman » Sun Dec 14, 2014 2:16 pm

Here is an updated picture.


Image


A couple questions: is the X-point a null point?

It is not the same configuration -- but wouldn't this null point have physics similar to the center of the polywell?

They talk about the FRC wanting to "flip over". I am trying to draw this. The process is an interesting interplay between the field and the plasma. I am not sure what starts what.

mattman
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Re: Can anyone walk me through Field Reverse Configurations?

Postby mattman » Mon Dec 15, 2014 1:47 am

Field reverse configuration. This is a plasma that self-organizes. It does this because a plasma is a fluid which conducts electricity. That means it can generate its’ own magnetic field. This structure is shown below.

Image

This was first observed in 1956 by accident. Researchers were doing a theta pinch. This is where current races around a tube of plasma. This makes a crushing inward magnetic field, squeezing material in the center.

Field reverse configurations have a beta value of 8 to 12.
On stability: Instabilities are a big problem. They start in three places: the border, X and O points. People talk about the tearing stability. What is this?

How are FRC formed? As far as I can tell the best way is with a reverse-theta-pinch (what is this specifically?) Here is a picture of one at LANL:

Image

I am not sure how this works. They give me a process of the configuration here:

Image

But this is hard image to follow. I need something better. There is A TON of papers out on FRC's. Way more than the polywell. But the configuration has several parallels to the polywell.

hanelyp
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Re: Can anyone walk me through Field Reverse Configurations?

Postby hanelyp » Mon Dec 15, 2014 4:28 am

mattman wrote:Here is an updated picture.


Image


A couple questions: is the X-point a null point?

Yes
It is not the same configuration -- but wouldn't this null point have physics similar to the center of the polywell?

They talk about the FRC wanting to "flip over". I am trying to draw this. The process is an interesting interplay between the field and the plasma. I am not sure what starts what.

Consider if the current loop/magnet axis is tilted slightly relative to the outside field. Each end of the plasma magnet is pushing against the near end magnet.
The daylight is uncomfortably bright for eyes so long in the dark.

D Tibbets
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Re: Can anyone walk me through Field Reverse Configurations?

Postby D Tibbets » Mon Dec 15, 2014 1:25 pm

A few comments on the previous few posts.

The illustrations show the B field of the outer lower field orientated to the right, both top and bottom should be oriented to the left, if the arrow indicates N (or S) both should be going in the same direction. It is a cylindrical solenoid B field .

I do not think there is a null B field point inside the field reversed configuration, certainly not within the FR portion. The B field in the center is generated by a plasma current spinning around in a torus and it thus has its own internal B field much like the individual wire windings in an electromagnet has its own B field. For there to be no gross (large scale) B field within the plasma there cannot be a preferred direction of motion like a one way spin around an axis.

I am not sure what causes or maintains the spin of the plasma that generates the field reversed B field. I suppose spin can be imparted to the plasma initially (shooting smoke rings into the machine,) but what maintains it? Once established, does the FRC B fields sustain the plasma spin? I suppose that the interaction may be similar to what is happening in a smoke ring.

Confinement, I think is due to the closed B field lines of the central reversed configured B fields. I'm not sure what happens in the region where the central B fields separate from and reverse from the outer B fields

The 8-12 Beta value presumably means 8-12%, otherwise it doesn't make any sense. Any Beta greater than 1 means the plasma pressure is greater than the magnetic pressure so that it contacts the the electromagnet can or otherwise exits the confinement area. Beta up to one is possible, but greater than one is synonymous with containment failure (I think).

Dan Tibbets
To error is human... and I'm very human.

asdfuogh
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Re: Can anyone walk me through Field Reverse Configurations?

Postby asdfuogh » Tue Dec 16, 2014 3:27 am

Useful paper (and its related papers):

http://scitation.aip.org/content/aip/jo ... /1.4884616

>I do not think there is a null B field point inside the field reversed configuration

Theoretically, the null-point (null-ring, really) is where that O-point is labeled. It is expected that the portion of ions near this null-ring region contribute to stability due to FLR effect.

Some more informative articles:

http://www.sciencemag.org/content/278/5342/1419.long

http://link.springer.com/article/10.102 ... 7.10861.bc

mattman
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Re: Can anyone walk me through Field Reverse Configurations?

Postby mattman » Tue Dec 16, 2014 11:04 pm

Hello,

Image


1. Where is the magnetic field pressure pointed in this direction?

2. Is it true (I read this in Hoffman 1986) that the plasma pressure inside the FRC is higher than the surrounding. (YES)


I found a video which shows how FRC's are formed. This is here:

https://www.youtube.com/watch?v=389NSERjuxc

I have a couple of questions...

Image

I can only assume that this thing is simulating this machine:

http://www.engadget.com/2013/09/12/peri ... ision-003/

The null points in FRC have the same behavior as the null points in Polywells - this evidence can be used/stolen for Polywell research.

Finally, there has been a ton of work done on FRC's. Here is a list of the projects over the years.

Image

Image

asdfuogh
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Location: California

Re: Can anyone walk me through Field Reverse Configurations?

Postby asdfuogh » Wed Dec 17, 2014 8:54 am

>The null points in FRC have the same behavior as the null points in Polywells - this evidence can be used/stolen for Polywell research.

Why would they? Polywell field lines wrap around the coils, and cusp out to the end of the device. What are the field lines which surround the null point of the FRC? They wrap back around and close on each other. The Polywell null point is one actual point. The FRC null point is a ring. So, no, you can't really use them for the Polywell research, not without comments like these. o-o


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