https://www.berryhillfh.com/obituary/ning-li?lud=4CF765EE88E...

Her claim that "You can take a bowling ball and place it and it will stay." is fascinating. I would love to see footage/video of this. Small electro marbles and globes are one thing, a bowling ball or other large non-magnetic object!? man oh man!

My explanation was definitely over simplified, but I'm not knowledgable enough to go into detail on the topic. I can't even point you towards something to read on the topic since everything I read about it is like 15 years old at this point.

“…the supporting structure can only withstand the forces if the interfaces between the ten individual segments of the central rings, which weighs several tonnes, are built with a level of precision of less than 100 millionths of a metre…” - and they found a small family business in the north of Italy capable of doing this!

1 meter = 100 cm = 1000mm.

So 1 millionth of a meter = 1/1000th of 1mm.

thus, 100 millionths of a meter = 0.1mm, or ~4 thou in American units. Easily achievable by hobbyists, let alone by serious, professional equipment.

Sure, that is a pretty exacting specification for what I suppose is a big machine, but I'm pretty sure very normal things like say, car engines get made to far tighter tolerances.

0.01mm is very difficult when you’re talking large custom objects with complex shapes.

   > bei Toleranzen von teilweise nur 0,1 Millimeter

Keeping it all in the same units until the end here:

1 millionth of 1 meter = (1 / 1,000,000)m = (1e-6m)

1 millionth * 100 = 100 millionths => (1e-6m) * 100 = (1e-4m) = 100 millionths

(1e-4m) = .0001m | 1m = 1000mm => .0001m*1000 = .1mm

I am to used to people saying 100 millionth of a meter to mean 10 nm or 0.01 µm which would have looked insane if I had written that.

1 thou was achievable in routine shops in the 1940s and a tenth of a thou (2.54 micron) is a common accuracy to target these days. Obviously it depends on the context and the size of the object, at some point you move away from cutting to using grinding and lapping to achieve your results, which is ultra-timeconsuming.

Getting the same finish on a 120"/3m coil is 33 ppm. 100 ppm / 0.01% for any operation or process tends to be where things start to get really challenging. Deflection goes up by the length cubed, so increasing the size of all the tooling relative to the tolerance gets really challenging really fast.

Or the very person that someone with a show like Art Bell would have as a guest.

Nuclear fusion occurs at extremely-high temperatures. As you heat your fusion fuel to sufficiently-high temperatures to allow fusion, the matter transitions into a plasma, which is great: plasmas react to electromagnetic fields. As such, a major challenge with achieving viable nuclear fusion is making a vessel capable of holding the fusion reaction. Because we can't create on-demand gravity wells, the next best option for confinement is using electromagnetic fields to hold the plasma in the air.

So, you now have an "electromagnetic bottle" capable of suspending a fusion reaction above the reactor's walls. Now, you have another issue: how do you ensure the fuel will sufficiently mix to sustain a fusion reaction? One approach is to move the plasma in a loop. The topologically-simplest method to accomplish this loop is the torus. Such a plasma-confinement device is called a tokamak. A tokamak uses two magnetic fields, torodial and polodial, to accomplish its task. The torodial field is driven through the plasma to push it forward, while the polodial field pulls the plasma in toward the center. Proper balance of these fields will allow the plasma to circuit the vessel following a helical path, achieving confinement.

However, driving two separate magnetic fields is energy-intensive, and a successful fusion reactor will want to minimize its own power consumption to maximize the amount available for external usage. Enter the stellarator. The stellarator also drives the plasma around in a circle, it but uses a single magnetic field. How? It "tricks" the plasma into "thinking" there's only one magnetic field by using computer-optimized magnets with highly-complex geometries. This provides stellarators with a major engineering advantage over tokamaks and is a primary reason Wendelstein 7-X would have chosen it.

With the confinement vessel topology largely identified, the next main step is to figure out how to build a vessel able to contain a sustained fusion reaction. For context, fusion experiments traditionally only operate on timescales of milliseconds to maybe a second. The reason? Fusion occurs at millions of degrees, and keeping the reaction vessel cool, ensuring a continuous supply of fuel, and dealing with reaction "exhaust" (e.g., alpha particles) and stray high-energy neutrons from the common deuterium-tritium reaction (which irradiate your reactor walls because neutrons don't react with electomagnetic fields) is a major, major engineering challenge. Any operational, net-positive fusion reactor must be able to operate for days, weeks, and months on end.

What Wendelstein 7-X has been attempting to do for years is demonstrate that building such a vessel is even possible. Their overall goal is to sustain a fusion reaction for about 30 minutes. Such a timescale will show a proof-of-concept system which enables sustained fusion reactions to occur.

Currently, the preferred fuel is deuterium-tritium because the fuel is generally available and has an attainable fusion temperature. The stray neutron issue can be mitigated by lining reactor walls with lithium to breed tritium fuel. Even better is to use the helium3-helium3 reaction, which completely annihilate to produce pure energy as the output (welcome to e=mc^2, enjoy your stay). The main holdups are: (1) the reaction occurs at much higher temperatures than deuterium-tritium, and (2) he(lium)3 is quite scarce on Earth. Once Wendelstein 7-X shows how to engineer a proper confinement vessel at a "lower" temperature, you can then work on the higher temperature levels required for he3-he3. Also, he3 is plentiful on the surface of the moon, so mining the surface of the moon will be performed to obtain the required fuel, which is the fundamental premise of the movie "Moon".

Someone asked for information on electromagnetic plasma containment folding. I recommend reading up on magnetohydrodynamics (MHD). It's the mathematical and physical foundation of your interest.

> By twisting the plasma into a shape where the curl of B (proportional to J) is parallel to B, i.e. a helix, the cross product is 0, and thus there are no net magnetohydrodynamic forces on the plasma.

Hope all that's a good answer for you.

> Mobius aspect

You might avoid using the word "Mobius" and instead use "helical." A Mobius strip is important because it has two faces which form a single surface. The surface aspect isn't relevant in this context, so a term which refers to the shape would likely dispel confusion in a reader.

As far as I'm aware, each section of a stellarator is periodic in its own right, which means the end and start points of each section are the same. Though I'm not certain, the choice of four versus five is more likely an engineering factor rather than one of physics, whereas the distinction between a tokamak and stellarator is of physics and not just engineering.

edit: changed language about the divertors.

The most precise term to describe the "twisted ribbon" flux tube in W7-X is "toroidal helix". The toroidal quality comes from the general torus shape of the stellarator, and the helix quality comes from the twisting of the magnetic field by magnets. (The torus shape is required only topologically; look up the knotatron to see what I mean.)

The "ribbon" we're talking about is properly called the flux tube. The flux tube is the volume created by the flux surface, which is where the magnetic field lines lie. A given volume of plasma contained within a flux tube should remain inside it, causing magnetic confinement of the plasma.

The optimality of the confinement of the flux tube is expressed with the term "omnigeneity". Conceptually, a flux tube has onmigeneity if ideally all of the non-colliding plasma inside the tube stays in the tube. W7-X's flux tube appears to be approaching omnigenity. (Another experiment which approaches omnigenity is HSX. Interestingly, HSX has one set of primary magnets, whereas W7-X has two. That's likely because HSX achieves omnigenity via quasisymmetry, whereas W7-X uses various stellarator optimization techniques.)

With these points, we can call the W7-X "ribbon" a near-omnigenous toroidal helix flux tube, which sounds way cooler. So, all that said, why is a helical property desired? From what I've read, the twist in the flux surface reduces plasma drift inside the flux tube.

I think it makes sense to analogize this stuff as a circular semi-permeable pipe filled with a high-pressure "magic fluid" flowing around-and-around inside. By semi-permeable, it means fluid will leak from the pipe if the internal pressure is too high (remember that this is magic fluid). Trying to understand the helical twist along this analogy, I think the effect is evening of internal pressure across the pipe surface to reduce fluid turbulence and permeation while maximizing laminar flow. At least, that's my best analogous interpretation of "why" the twist helps.

The divertors are useful for long-term reactor operation but have no direct relevance to the magnetic field geometry. I'm guessing there's two divertors for engineering reasons (performance, redundancy, etc.) and not for reasons of basic physics.

Is that what you are saying ? Or are there other constraints on the number of twists (e.g. must be odd, ...)

It doesn't completely annihilate to produce pure energy. It produces helium-4 and two protons. Or you can react helium-3 + deuterium to produce helium-4 and one proton. The point is that helium-4 and protons are easier to shield against than neutrons, don't turn your reactor radioactive, and at least in theory their energy can be extracted directly (eg through induction) instead of through heat.

Edited to add: except helium-3 + deuterium still produces neutrons, because sometimes the deuterium will react with itself to produce helium-3 and a neutron.

Here's an interesting link which lists various fusion reactions: https://en.wikipedia.org/wiki/Helium-3#Nuclear_fuel

This is repeated a lot, but the practicalities are... questionable. Here's an article I consider to be the definitive criticism of the concept:

https://www.thespacereview.com/article/2834/1

I want to be able to think in mobius, but my brain is currently like, "No thanks."

The core concepts in mobius-land are local curvature and global cumulative field.

Then you accidentally make something truly 3D by intersecting things and realize you have no idea what you're looking at, couldn't imagine it if you closed your eyes, couldn't replicate it if you had a picture of the result and didn't know the 2D inputs that made it... and then you realize there are probably people out there who can see that entire design in their head.

To me it's like unicycling on a tightrope or skateboarding or realistic oil painting or playing piano well. I have no real concept or reference point for what that experience must be like.

I can't figure out any kind of way someone could do that with anything resembling what I understand "thought" to be like, so I assume you must be able to process entire sequences and their alternate possibilities simultaneously?

If true 3d printing* ever gets cheap, it'll be interesting to see how much form will be able follow function, rather than manufacturing cost.

* true 3d, as in overhang are allowed. Something like a cheap FDM is more 2.5d, since overhangs aren't allowed.

They're not quite unconstrained, and the layer adhesion strength makes some geometries not strong, but they're much more than 2.5D.

I think for me, the prerequisites for mastering CAD were 1) the practice I got visualizing 3D shapes so I could translate them into unambiguous mechanical drawings on paper (I swear, I'm not that old but my college was behind and we were the last class to actually do mechanical drawings with a pencil), and 2) having a procedural thought process from coding so that I could sequence the CAD operations to get where I want.

It's a block language where you program the object rather than manipulate shapes. It works well for my brain. Ymmv

I'm not a mechanical engineer, I mostly only do incidental CAD and hobby level work, so it's not really essential to have the deep understanding of space that real MEs need.

I often don't know what sequence of operations I'll need until I actually open the app. Generally it's more of an "Oh I need a mounting hole, lets look around on the screen and see where one could go" thing, a lot of the thinking is in the app rather than in the mind.

Of course you can't make nicely parametric things without a lot more thought so I will often wind up having to redo things that aren't one offs...

https://www.microwavejournal.com/articles/21001-printed-reso...

I have no idea if there are any advantages over a simple planar circular loop though.

2. Alternating currents will dissipate even with zero resistance, because the circuit will emit EM waves.

Those crazy electromagnets they use on these stellarator are simple superconducting loops that they 'charge' by inducing a current. That current is maintained so long as the superconductor stays below a certain temp. There is even something called a SMES (superconducting magnetic energy storage) that stores power this way, as I understand it they have a 0% self discharge rate.

If you have a hypothetical continuum of charges moving in a circle, and you use Maxwell’s equations, you’ll find that given a constant charge density, no EM radiation will be emitted.

If you have a superconductor, you should really be using quantum mechanics to understand it. If you can imagine that an electron can “orbit” a nucleus without emitting EM radiation, then you can imagine that current can flow in a loop without emitting EM radiation. The behavior cannot be explained by thinking of the behavior of a single electron, but must be explained by considering the behavior of many electrons in a quantum mechanical system.

Also note that the actual speed of electrons (the “drift velocity”) moving around a loop of wire is extremely low, so if you treat electrons as point charges and ignore quantum mechanics, and you calculate the amount of EM radiation that should be emitted by a typical loop of wire, you will get an extremely low amount EM radiation emitted, which would be very difficult to measure.

I spent a lot time staring at Escher images as a teen, so I think my brain says "yes please". I have no idea what to do with any of it, so it's not like it does me any good.

That explains why folding is important, as for the mobius, I oversimplified a bit. The Wendelstein has 5 folds, making it a mobius, but I think I read about one in Spain that had only 4 folds. That would mean the mobius isn't imperitive, but I'm sure there is a good reason for it.

Really a stellerator doesn't need 'folding' at all, they can be as simple as a twisted torroid. I didn't want to go into excruciating detail though, the more in detail I go the more likely I am to say something that is wrong lol.

Edit: I looked it up, the one in spain is called "TJ-II"

That effect works both ways too, where a single wire with a digital signal will spew out radio waves, 2 wires with opposing signal cancel each other out and emit no em waves.

The effect with the stellarator is more like stirring a pot.

With mobius strip you regularly flip between inside and outside, so the plasma particles get more even force applied.

Draw a torus and then draw rectangular "bands" across it, they will represent the containment magnets.

Due to pure geometry, the area closer to the center will have a smaller distance between bars. This means that the magnetic field will be stronger near the center.

This in turn means that particles will separate (depending on charge) and drift to the sides. It seriously interferes with the containment.

You can fix that by changing the torus into something resembling "8", so that particles move to one side when they fly through the upper part, but then they'll move back as they fly through the lower part.

Of course, you can't just do that in 2D because the part in the middle of "8" will have no magnetic field. You need something without self-intersections. You can try to move one side up and another down. But that doesn't quite work either because you will get another set of preferred directions.

So instead you go with the gentle twisting, resulting in the Möbius-looking shape.

What's even more interesting is that the fusor - the simplest possible design for a thermonuclear reactor, so simple that anyone skilled in electrical engineering and having access to proper civilan equipment can build one with ease - seems to be invented _after_ both stellarator and tokamak.

That said, I never particularly liked stellarator design. The very _complexity_ of it somehow feels subtly wrong, like doubling down in the wrong direction.

However, this is one of the cases where I would absolutely love to be proven wrong. We are far past due big breakthroughs in the field.

In the long run, it's not known stellarators will be the eventual winner in the long race for a viable fusion reactor. The attributes in a winner will be net-positive operational efficiency and superior energy harvesting abilities. Perhaps multiple approaches will be viable.

To be honest, I've been interested in the domain for quite a time and I still want to build a fusor or a polywell at some point just to see it glow. Probably won't happen though.

This made me think of modern jet fighters being designed to be aerodynamically unstable, making them all but impossible for human pilots to operate without flight computers. Apparently the maneuverability benefits make the added complexity more than worth it.

https://en.wikipedia.org/wiki/General_Dynamics_F-16_Fighting...

    > The very _complexity_ of it
    > somehow feels subtly wrong.

I understand that it was hard to build, but isn't that just because it's a one-off?

Any one part of the inside of it looks no more oddly shaped than the outside of any modern car, and we've managed to scale that.

I read an article a while ago which sold me on the stellarator that said something like: "The tokamak has magnets in a configuration that gives simple engineering but hard physics, whereas the stellarator has hard engineering to make a complex magnet but that results in simple physics".

The engineering is a much more understood beast. It was still fairly novel as they had to have a computer do the design of the magnets, but that is now a solved problem. But then if that allows us to simplify the (very difficult and novel) physics it feels like the "obviously" correct decision.

The other thing that makes me a stellarator fan is that the JET/ITER work is later and more expensive that predicted at every stage. The W7-X provided a plan for the runs they wanted to do and upgrades to the reactor and they have basically run entirely to schedule.

it’s a fair demand to make, given that his TV predecessor was called Scotty and DID have a Scottish accent

https://www.youtube.com/watch?v=4PG5PCd284o

Edit: But as to the why, it's fun. Just like the "input/output translation" trickery.

If you listen to this with headphones, or speakers with decent separation, paying attention to this feels interesting. It's similar to the way listening to "binaural beats" can do interesting things to your brain.

Also if you are in the habit of putting an entire album on repeat and this is one of your favorite albums, then you've probably heard this a zillion times. If you have your music player set in "randomize by album" mode, then, well, it's the first track on this album, so every time it comes up you'll hear most of it unless you instantly decide you are not in the mood for Orbital 2, and even if you're not in that mood it may be pleasant to let everything come back into phase before going to another album.

----

The next track on the album starts up entirely in the left ear, with a tinny, distant little loop, and the words "Even a stopped clock tells the right time twice a day". Once it brings in a deep bass, this bass is also doing some weird cross-ear phasing things.

And then the third track also opens with "Even a stopped clock..."; a theme has been established at this point. Time is a loop, and a stopped clock is right twice a day. The opening of "where time becomes a loop" is also a bit of a joke; Orbital's musical craft is very much about making a bunch of short loops that work together, and bringing them in and out over each other for four to seven minutes. Occasionally as much as thirty minutes, the extended version of "The Box" is glorious. This is something that utterly dominates most electronic dance music now, but Orbital was one of the first notable acts to really go hard on this, and this is their second album; they are saying "yes it's just more loops, we think they're good loops, enjoy!".

By the time you get to the last track, you've probably forgotten about Worf's repeated mantra. Especially if it's your first time listening to the whole thing and Halcyon + On + On just blew all the cobwebs out of your head. But Orbital returns to the idea, with two different loops that are very close in sound and length, played on both channels: "Input Translation"/"Output Rotation". They begin in phase with each other, drift out, and come back together. And the album is over.

Or, if you have the CD player on repeat (remember, this album is from a time when people bought CDs and probably stuck them into a one-disc player, maybe a 3 or 5-disc player if they were lucky, and the whole album is built with an awareness of this), you're back where you began, inputs translated and outputs rotated, and ready to be reminded of the Theory of the Moebius.

Time has become a loop. Come out of the trance Orbital has put you in. Do you want to experience this loop again? Does it feel rude to jump to another album before Worf's come back into phase again? You may as well let him get you back in sync with the moment the album began before going back into normal time.

You just describe the first time I every danced with Lucy. I went back and forth with this disc and The Orb's A Huge Ever Growing Pulsating Brain That Rules from the Centre of the Ultraworld.

is this where we talk about

- the 39:59 mix of The Orb’s “Blue Room” (which, like several other Orb singles, is better than the album version thanks to Jah Wobble providing a proper bassline)

- the academically-verified lack of repetitiveness in Autechre’s “Flutter”

- and Orbital’s “Criminal Justice Bill?” on the “Are We Here” CD single, which is four minutes of silence

The Orb Live '93 CD was one of those that if a CD could wear out like a cassette, that would have been one (two technically) that would have from my collection.

Those two albums sound like a pretty good soundtrack for making a good trip more likely!

They should've gone with a catchier name like "forbidden cruller".