Talk:Stellarator

Configuration taxonomy

Mentioning the configurations (Torsatron, Heliotron, and Helias) is a good idea, but the recent edit is incomprehensible. --Art Carlson 18:33, 31 May 2006 (UTC)

The description is entirely unclear as to what it is and how it works in comparison to a toroid, particularly the flow of plasma. Oc1 1st 2006 Anonymous Coward

Agree that it's very unclear. Here's an outline suggestion, based on building up a taxonomy of confinement schemes with their problems.

1. No force on a particle from v-parallel. (Define v-parallel in the article, or point to an explanation somewhere else in the magnetic confinement pages. I'm assuming the Talk participants know it, and it's gotta be somewhere near here.) So particles' motion along field lines unconfined. Solution: have a toroid and bend the field lines back to meet themselves.
2. Oops. Particles still not confined very well. Single particle motions are still good enough to predict the problem, and it's B x grad B drift. Maybe point out that grad B is a consequence of bending into a toroid. Solution: twist the field lines so along-the-field-lines motion carries the particle back to the inside of the toroid.
3. How to twist?
   1. Current in the plasma. This way lies tokamaks.
   2. More complicated external fields with poloidal components. This way lies stellarators.

JohnAspinall 17:21, 7 September 2007 (UTC)

I notice that a lot of this taxonomy is already present (as it should be!) in Magnetic_confinement_fusion. The right solution is probably to improve that description (see my comments there) and make copious references back from here. JohnAspinall 17:51, 7 September 2007 (UTC)

Inside/outside or top/bottom

I don't know much about stellarators or tokamaks, but this section doesn't seem right:

"In a standard torus plasma particles (ions) on the inner portion of the tube are subjected to a greater magnetic force than those at the outside. Only particles near the middle receive the optimum amount. Since magnetic forces are generally at right angles to motion, non-centered plasma moving around the toroid would be forced up or down until it hit the edges of the tube. In a stellerator, when a particle orbits the tube, it spends half the time on the inside of the tube and half on the outside. This helps to equalize the forces and the particle is subject to a much smaller drifting force."

It's my understanding of the geometry of a tokamak that because the outer circumference of the toroid is much larger than the inner circumference, the wiring of the electromagnet is much more spaced out on the outer edge of the toroid, making the magnetic forces there much weaker than the densely wired inner edge, and that's why the figure-eight shape is used in a stellerator, since in a figure-eight, the outer edge of one side becomes the inner edge of the other side and vice-versa.

So I don't understand the up/down reference in the last part of the 3rd sentence. What would cause the particles to move up/down? Shouldn't the imbalance just cause the particles to move outward horizontally (away from the center of the toroid)? And if the particles were being forced to the top/bottom edges of the toroid, how would a figure 8 shape attenuate the drift force? Am I missing something here? Again, I don't know much about this subject, so I apologize for my ignorance. I'm just having a hard time understanding that portion of the article.--Subversive Sound (talk) 01:25, 9 March 2010 (UTC)

The resulting field has a gradient from inside to outside. As an ion circulates the device (which they do, quickly) and thus creates its own current, the right-hand-rule states that the force will be at right angles to the current and the gradient. So, up or down. Maury Markowitz (talk) 15:02, 10 November 2010 (UTC)

Picture

This article contains a nice diagram; however it is a diagram of a tokamak, not a Stellarator. Even if it clearly states that the pic is a tokamak, the casual reader will glance at the text and move on, thinking the Stellarator has the shape of a donut. As we all know, a picture says equal to or more than 1001 words, so....Spearman (talk) 11:00, 28 February 2012 (UTC)

Inclined to agree. I've added a picture of a stellarator to the lead, but I think that unless we can provide a diagram of a stellarator for comparison, it's probably better not to have the diagram of a tokamak, even in a section clearly labelled Comparison to tokamaks. It's a great diagram but it belongs in the articles on tokamak and on magnetic confinement, not here. Andrewa (talk) 19:06, 11 September 2012 (UTC)

Divertor

Article currently [1] reads in part It is much harder to design a divertor (the section of the wall that receives the exhaust power from the plasma)... which I think is misleading. ITER will not generate any power at all, nor does any other tokamak or stellarator currently or previously running or under construction. Whether DEMO will harvest heat only from its divertor (as this implies) or whether heat escaping from other areas can also be harvested is not at this time decided. Andrewa (talk) 18:59, 11 September 2012 (UTC)

What is quasi-symmetric field

Its mentioned in recent results - but not distinguished from the configurations listed above. - Rod57 (talk) 14:23, 5 December 2015 (UTC)

Spherical stellarator

Just an external link at present - seems worth a brief mention somewhere eg. if it has any possible advantages ? - Rod57 (talk) 14:23, 5 December 2015 (UTC)

What configuration did Spitzer build in 1951

Princeton Plasma Physics Laboratory doesn't say either. It would be great to have more details on what was built 1951-1958 and what results. - Rod57 (talk) 15:22, 5 December 2015 (UTC)

have updated PPPL to say figure-8 and listed some. - Rod57 (talk) 22:09, 12 December 2015 (UTC)

Wendelstein 7-AS seems worth mentioning

[2] says "The first attempt at a partially optimized stellarator, dubbed Wendelstein 7-AS, was built at the IPP branch in Garching near Munich and operated between 1988 and 2002. It broke all stellarator records for machines of its size. " - Rod57 (talk) 22:09, 12 December 2015 (UTC)

Unsourced 1

The following is almost entirely unsourced; moved here per WP:PRESERVE. Per WP:BURDEN, do not restore without finding reliable sources, checking the content against them, and citing them.

Description

Background

Early fusion research generally followed two major lines of study; devices that were based on momentary compression of the fusion fuel to high densities, like the pinch devices being studied primarily in the UK, and devices that used lower densities but longer confinement times, like the magnetic mirror and stellarator. In the latter systems, the key problem was confining the plasma for long times without the hottest, most valuable, particles escaping from the device.

As plasma is electrically charged, and thus subject to Lorentz force, it can be confined by an appropriate arrangement of magnetic fields. The simplest to understand is a solenoid, consisting of a helix of wire wrapped around a cylindrical support. A plasma inside the solenoid will experience a force toward a guiding center of its orbit which moves only parallel to the applied field. However, in this case the plasma would see no force along the long axis, and would rapidly flow out of the ends of the solenoid and escape.

One solution to that problem is to simply bend the solenoid around into a ring, closing the ends. However, in this case the magnetic field is no longer uniform. The electrical windings on the inside edge of the toroid are closer together, and further apart on the outside edge. This leads to a weaker field on the outside than the inside. A particle's orbit will have larger curvature on the inner limb of the orbit than on the outer, leading to a net migration away from the center of the torus. These particles will eventually drift out of the confinement area.

Stellarator

Stellarator magnetic field

The early history of fusion research is dominated by efforts in the UK using the pinch technique, with small experiments beginning in 1948. The revalation that Claus Fuchs was passing information to the Soviet Union led to this work being classified. Small efforts in the US and Russia were also underway, but none of these were made public.

The concept of controlled fusion power was made public in February 1951 when Argentina claimed to have invented a working fusion reactor. While preparing for a ski trip to Aspen, Spitzer's father called and mentioned an article on the topic in the New York Times. Looking over the description in the article, Spitzer concluded it could not possibly work; the system simply could not provide enough energy to heat the fuel to fusion temperatures. However, the issue stuck with him, and he began considering systems that would work. While riding the ski lift, he hit upon the stellerator concept.

Spitzer's innovation was a change in geometry that reduced the drift seen in a torioidal confinement system. He suggested extending the torus with straight sections to form a racetrack shape, and then twisting one end by 180 degrees to produce a figure-8 shaped device. In a torus, a particle that starts on the "inside" of the device remains there while it circulates around the long axis. This is what causes the net drift compared to particles on the "outside". In the stellerator, when a particle is on the inside on one of the curved sections, by the time it flows through the straight area and into the other curved section it is now on the outside. This means that the upward drift on one side is counteracted by the downward drift on the other.

To allow the tubes to cross without hitting, the torus sections on either end were rotated slightly, so the ends were not aligned with each other. This arrangement was less than perfect, as a particle on the inner portion at one end would not end up at the outer portion at the other, but at some other point rotated from the perfect location due to the tilt of the two ends. As a result, the stellarator is not perfect in terms of canceling out the drift, but the net result is to so greatly reduce drift that long confinement times appeared possible.

Newer designs

The basic idea of the stellarator is to use areas of differing magnetic fields to cancel out the net forces on a particle as it travels around the confinement area. Spitzer's concept used the mechanical arrangement of the confinement area to achieve this goal, while more modern systems use a variety of mechanical shapes or magnets to the same end. A common arrangement uses a series of coils arranged in a helix around the toroid, creating an electrical analog of the mechanical layout.

In contrast, pinch devices and the tokamak rely solely on magnetic fields for confinement, but add additional confining forces to the mix by running an electric current through the plasma itself. These currents can produce powerful confining forces, but are themselves a source of instability in the plasma. As currents were ramped up during the 1980s it appeared that they might represent a serious problem to further improvements in confinement, and the all-magnetic stellarator designs saw renewed interest.

References

-- Jytdog (talk) 21:40, 26 February 2017 (UTC)

Unsourced 2

The following is almost entirely unsourced; moved here per WP:PRESERVE. Per WP:BURDEN, do not restore without finding reliable sources, checking the content against them, and citing them.

Comparison to tokamaks

Tokamak magnet field and current

The tokamak provides the required twist to the magnetic field lines not by manipulating the field with external currents, but by driving a current through the plasma itself. The field lines around the plasma current combine with the toroidal field to produce helical field lines, which wrap around the torus in both directions.

Although they also have a toroidal magnetic field topology, stellarators are distinct from tokamaks in that they are not azimuthally symmetric. They have instead a discrete rotational symmetry, often fivefold, like a regular pentagon.

It is generally argued that the development of stellarators is less advanced than tokamaks, although the intrinsic stability they provide has been sufficient for active development of this concept.

The three-dimensional nature of the field, the plasma, and the vessel make it much more difficult to do either theoretical or experimental diagnostics with stellarators. It is much harder to design a divertor (the section of the wall that receives the exhaust power from the plasma) in a stellarator, the out-of-plane magnetic coils (common in many modern stellarators and possibly all future ones) are much harder to manufacture than the simple, planar coils which suffice for a tokamak, and the utilization of the magnetic field volume and strength is generally poorer than in tokamaks.

However, stellarators, unlike tokamaks, do not require a toroidal current, so that the expense and complexity of current drive and/or the loss of availability and periodic stresses of pulsed operation can be avoided, and there is no risk of toroidal current disruptions. It might be possible to use these additional degrees of design freedom to optimize a stellarator in ways that are not possible with tokamaks.

References

-- Jytdog (talk) 21:41, 26 February 2017 (UTC)

@Jytdog: The last time I checked the idea behind the Wiki was to create a repository of information, not delete it. Is it too much to ask for you to do a little work before simply wiping out whole sections of articles? All of this is trivially easy to cite in Google books, could you not spend five minutes doing so? Maury Markowitz (talk) 01:59, 28 February 2017 (UTC)

Please feel free to do so. Per WP:BURDEN do not restore the content without find refs, making sure the content is actually accepted knowledge and not just garbage added to WP, and then citing the sources when the content is restored as much as can be. Jytdog (talk) 02:40, 28 February 2017 (UTC)

New content

User:Maury Markowitz thanks for adding content. You are going to add citations to the sources you are drawing this from, yes? Jytdog (talk) 23:53, 11 April 2017 (UTC)

I'm drawing from references already in the document. Maury Markowitz (talk) 01:15, 12 April 2017 (UTC)

Would you please cite them, where you have used them? Thanks. Jytdog (talk) 02:28, 12 April 2017 (UTC)

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Neutral Beam Injection

Article states "Notable among these was the 1964 addition of a small particle accelerator to accelerate fuel ions to high enough energy to cross the magnetic fields, ..." While one of the stages of neutral beam acceleration is accelerating an ion, that ion is neutralized before being injected into the Stellarator plasma. It is a neutral particle that is crossing the Stellarator magnetic fields. Perhaps this should be clarified? 73.99.213.182 (talk) 13:27, 31 May 2021 (UTC)