Talk:Levitated dipole

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Hello All,

This article could be SO much longer. I am going to add tons of information, the LDX team at MIT have put much of their content on the web for everyone, so there is no issues with paywalls. I have a couple of questions:

1. Why does the geometry of the LDX suppress bred tritium?

2. Was the original dipole encased in stainless steel or inconel? I have read papers which said both at different times.

3. Getting the correct plasma behavior, on this page, in a simple way, is the ultimate goal here, what data did the LDX team get for plasma density, temperature, diamagnetism?

4. What picture does this provide for us on plasma behavior (including how the fields behave)?

Some questions/ideas/problems with this article:


"It is believed that such an apparatus could contain plasma more efficiently than other fusion reactor designs.[1]" Why justifies this claim? Better would be describing in more detail which variables of the device potentially enable it to be more efficient than, say, a normal tokamak, or an ICF experiment.


I have general issues with the order information is presented here. It may make more sense to present Hasegawa observation first. There also could be more details, perhaps a timeline of events done to make the LDX.

Second paragraph better than the first, but could use a better first sentence. We definitely want to include the dates associated with the Nature physics article.

The Machine[edit]

The Dipole[edit]

What is the best way to refer to this, should we call it a device or a machine? What is a rutherford cable? Can we create an article on this topic? Can we link or at least put in a sentence on what this is. Can we come up with a better description an inconel donut magnet?

I cannot follow - or visualize - a "counter wound ring of currents". Is this a system of two current loops inside the donut with current flowing in different directions? Can we get an accurate picture of this? Is it two rings of a wire looping around in both a clockwise and counter-clockwise manner? If we are doing that, can we link these directions to the direction of the magnetic field?

It would be useful to have some numerical references. For instance, if the ring weighed 450kg perhaps we could mention that the average human is 62kg, or some common object comparison. This could bring perspective. Same for the 5 tesla field – can we compare this to something common?

I looked at the captions of the dipole pictures, and found it simply lacking. For example, I was not sure how the liquid helium actually cools the device. Does it "flood" the system, or does it cool radially from some central loop?


A charging coil is mentioned, and that the "dipole would charge here", but there is really no description of what that means. One or two sentences of how the charging occurs, with a link to the induction article. Is the dipole experiencing a magnetic field induced upon it? Does this generate stored current?

This section could be worded better... "the dipole's magnetic field is first induced while non-levitating. It is raised manually using supports. Finally, outside Helmholtz coils (that produce an external mag field) are used to levitate the dipole.

We need more detail about how the plasma is formed? Presumably this was done with a low pressure gas, heated with the radio frequency. What gas? What pressure? How long? How much RF energy was used?

I want more general information about the plasma created. Can you tell me what the plasma temperatures, densities and ionization fraction was?


One general issue is that the reader has no sense of where the diagnostics are inside the machine. For each one of these tools, we need to know its’ name and what it does.

X-ray Detector - Of course it is "good for measuring electrons"... the description of this diagnostic feels like it shoves in a bunch of other information not relevant to the levitating dipole.

Langmuir probe - again, where is this diagnostic in the device? Also what is an "emissive" probe? This implies there are different types of Langmuir probes, right? What are triple and a dozen Langmuir probes. Why are they there? Why does the device need this? Redundancy? Statistical accuracy of the measurements?


I feel like this entire section should be higher up on the page. This is very important information about the device – how it works and what it does. "This behavior has been called a turbulent pinch" there is no source or reference given for this statement. "The plasma was trapped fairly well.” What does fairly well trapping mean exactly? A beta number here is introduced. I do not know what this ratio is.

Modes of Operation[edit]

Too little information here. I have no idea how these two modes make the operation of the device act differently. Also mentions this in a somewhat "historical" perspective which makes it feel like it’s in the wrong section or order.

Tritium Suppression[edit]

Secondary tritium could be partially removed... but how? There is a missing explanation here...

I think the title here is a little misleading. It never defines "tritium suppression". Instead, the text tries to convey many things: fuel choices, the pros/cons of fuel, potential implications on the device based on fuel choice... generally this is not a focused paragraph


I'm left with a feeling of incompleteness and a bit of disorder to the information

I'm still not sure how the superconductivity really plays into the device’s operation. Is it simply that it keeps the dipole cool so that it doesn't fry? That's it? Has superconductivity been used a lot in other devices with less or more impact on the plasma or fusion? What, exactly does the superconductivity enable for fusion to take place?