Real Fusion making Great advances

I am confident General Fusion's method will fail, because they will not be able to achieve either 1) symmetrical target compression, which is required, or 2) repeated reactions, because each reaction cycle will create splashing and turbulence. Even if they can get one good shot, they will not be able to create repeated shots necessary for useful power generation.

Quote from Longview

Modularity and easily indium-soldered coils allows "yearly" removal of activated vacuum chamber in a single 40 T lift, w/o piecemeal "hot" disassembly

[Note: See Longview citation in next post below, nickel among other components is apparently "out"]

My first critique here would be that a "low neutron activation" steel might also be quite ferromagnetic, and hence act to shield the plasma from the 10 T magnetic field, at least to some extent.

I don't know the composition of such 'low activation' steels, but they must have lower or more desired neutron cross section.

So the vacuum chamber surely remains a tricky interface-- that also is subject to huge neutron flux. Regardless of alloy, I am guessing that the molten salt might be quite corrosive at the near 500 C working temperature,

Quote from Longview

So the vacuum chamber surely remains a tricky interface-- that also is subject to huge neutron flux. Perhaps a work-around might be a monel metal chamber, that is isotopically defined ~75% nickel and 25% copper. Regardless of alloy, I am guessing that the molten salt might be quite corrosive at the near 500 C working temperature,

And at this excellent ppt presentation by Nadine Baluc:

https://gcep.stanford.edu/pdfs…Yg/baluc_fusion_05_06.pdf

I see nickel is quite generally out, so no Monel metal. Silicon carbide is a very good first surface material. Beryllium is a strong candidate as well. Oxygen is generally not a problem. Lithium ceramics are mentioned. Bottom line: hot fusion has a huge problem with neutron flux and activation of materials. They clearly recognize this and will / are again spending taxpayer's money ($US, Euros and Yen) at rates for which, in my humble opinion and in view of hot fusion "issues", there should be say a mandated 5% surtax on such hot fusion research to fund alternatives such as LENR.

Ferromagnetism IS mentioned very briefly as a problem. Not easily overcome, I suspect. Since nickel is out, all forms of austenitic, non-magnetic, stainless steel are out as well. High chromium, low molybdenum steels are generally OK from the activation standpoint (1000 years or so to decay to "hands on").... but perhaps not from a ferromagnetic perspective. There appear to be some non-magnetic, low nickel steels in commerce. See: http://www.nyk.co.jp/en/produc…ys/nonmagnetic/index.html

General Fusion failed to perform a critical proof-of-principle experiment: demonstrating symmetrical compression of a fluid vortex from impact. They could have done this with water or low melting point metal, for example.

It would seem that compression in the axial direction will be difficult because of conservation of angular momentum. The spinning liquid metal will resist collapse to the axis of rotation. So, there may not be enough compression axially. Will the plasma simply squeeze out in the axial direction?

Quote from Max Nozin

Ferromagnetism is not a problem if magnets are inside the walls;)

No, the coils and the magnetic field are outside the vacuum chamber. The working vessel cannot be ferromagnetic, otherwise it will strongly exclude the externally applied field. "Wall" here might be the misunderstanding. This "wall" being the one nearest the vacuum, likely exposed to neutron flux from the D-T fusion. Ideally, a wall holding in place a lithium blanket. In this MIT design, Dennis Whyte seems confident that taking out "40 Tonnes" of inner chamber every year or so and burying it will work well. Although the slide I saw had "40 T", so maybe that was an optimistic read on future or eventual Teslas of magnetic field (but which were earlier specified at 10 T).

40 tonnes of chamber seems like a lot in this case. Assuming that "wall" is 10 cm thick and the outer diameter is 3.2 meters and the inner diameter is 1.6 meter (for an ideal torus, which this approximates). A little calculation gives approximate volume for the whole toroidal chamber: if the "wall" is 10 cm thick the volume of chamber wall is around 1.895 meters cubed. That would be 14.876 metric Tonnes of say steel, given a 10 cm thickness.

We have to guess that there is something more massive about this toroidal "wall" than suggested by the 'off the cuff' dimensions I took from Whyte's slide. Nevertheless that is a lot of material to bury each year for each operating reactor, even at about 15 tonnes.

Quote from Max Nozin

The magnets are I inside of the blanket.

That would be a very challenging design! No more superconductivity, no more Curie temperature, likely then no more ferromagnetism.

But from your link I see this:

"These are produced by superconducting coils surrounding the vessel, and by an electrical current driven through the plasma."

Strongly suggesting that the magnets themselves are outside the plasma chamber.

Quote from Debarium

It would seem that compression in the axial direction will be difficult because of conservation of angular momentum. The spinning liquid metal will resist collapse to the axis of rotation. So, there may not be enough compression axially. Will the plasma simply squeeze out in the axial direction?

To play "angel's advocate" here: I suspect the rotating Pb / Li working fluid is rotating at a moderate velocity and hence the pressure differentials are quite insignificant when measured against that of the coordinated summation of the hydraulic rams, and in comparison with the not insignificant inertial overshoot that carries the last few mm of compression. The axial rams could be designed to compensate for the lack of centripetal force in those regions. I suspect the whole working surface computation compensates every region of the sphere for such differentials.... which in any case are ultimately minuscule compared to the final hydraulic and inertial forces.

Quote from Max Nozin

The article also shows how just in 3 years the size increased 100 times. Gotta be model bias.

Yes, crazy. In my humble opinion, Lockheed got (or will get) snookered much more deeply than IH on that project, which also had an unconventional 'guru' advocate. We see that the public and managing MBA types are very often being asked to make increasingly sophisticated technical judgments as to the wisdom of big ventures-- while they and their constituent stockholders, aka the general population, become increasingly ignorant of basic sciences.

From a 50,000 foot view, the tolerances that must be satisfied to make any of these fusion reactor proposals operational would clearly result in a Rube Goldberg contraption prone to breakdown and needing constant maintenance. That fact alone warrants putting small but significant and sustained speculative money into serious scientific followup on the results of even poorly carried out LENR experiments, just to see if there is gold anywhere there.

Quote from H-G Branzell

I am pessimistic. How can a pressure wave reach the center if there is a hole there?

Molten metal splatter seems more probable.

Again as 'angel's advocate', and just my guess: In the end, if not now, the D-T fuel will be inserted in a little container much as it is in the NIF model. The density of the container and contents will be neutral with respect to the surrounding Pb / Li liquid, hence no tendency to drift from its implanted position over the < 0.5 second to "firing". That is the insertion will be in a fraction of a second before the rams are driven. The little 'hohlraum' will be constructed so as to be easily removed or to easily dissolve into the molten Pb / Li working fluid. There will be little or no possibility of "splashing" since the working fluid will be completely contained on all sides. Ideally, at least, not even a "bubble" in the center.

Quote from Max Nozin

did you [see] the diagram. Picture worth thousand words.

Yes, but not necessarily the same one you looked at. What I saw was the space filling line plot (my name). I don't see much there other than a gold colored "ring" which I take to be the plasma vessel, then all the rather space filling lines outside of it, which I take to be the magnet and supporting structures.

Quote from Max Nozin

I've been a huge fan of general fusion util the scope of mechanical issues became apparent.

What moderate rotation speed would you need to form stable vortex in liquid metal? Can you still call it moderate?

Can they put ram at the axis. Probably not. That is where the plasma injection ports are located.

Even after they solve all that, what material the sphere should be made of to withstand thermal/nuclear shocks and hammering by huge rams 100000 plus times a day?

Same here, but that has diminished over the decades, especially with models like Lockheed is proposing that seem so ignorant of all that went before.

Speaking speculatively and again as an unpaid 'angel': I don't think the GF model actually requires any rotational speed-- there is no need for any vortex-- that was just a working idea on how to sustain a little plasma chamber. If the "injection" of the little hohlraum is through a rapidly occludible port in middle of the one axial (if indeed an axis needed) ram it only requires a lockable piston on the face of that axial piston (here a diagram would be worth a thousand words, but I don't want to be that specific anyway).

So, just as with NIF, the plasma might not be injected as a plasma. But, if even it is needed, it could be generated inside the hohlraum compressively. From a compression induced fusion model, it may well be beneficial to retain some un-ionized fuel components-- appealing perhaps to a CF / LENR notion of "p-e-p-e-p" to "sneak up" on coulomb.

That IS a lot of impacts, and that is roughly what they are advocating. Of course, in 1888 we all would have been shocked to know that eventually the Otto cycle engine would happily endure huge pressures in each cylinder not 40 to 50 times per minute at a compression ratio of 3 or 4 to one, but up to 2500/min or more with compression ratios of over 10:1 in production engines easily running 100,000 hours. Not to neglect up to over 10,000 "impacts" /min in specialty racing engines of admittedly much shorter life. [note: numbers of cycles above divided in half for the 4 stroke cycle paradigm to exclude the much lower pressure scavenging / intake cycle].

Not that there is much in common between hot fusion and internal combustion, but only as an example of what engineering eventually accomplished in a somewhat analogous situation.

Quote from Longview

I don't know the composition of such 'low activation' steels, but they must have lower or more desired neutron cross section.

Longview : The crosssection of the blanket must be very high and be able to catch all possible neutron speeds from 0..24 MeV... Not low!

The neutron catching elements should be able to decay into harmless elements within a reasonable period. The secondary radiation should be easy containable (second blanket - lead) Neutron should not activate the coils, what is the most severe/challenging problem. Activated coils certainly will loose their their designed properties.

Here some interesting fusion related work - also military one from Sandia Labs:

http://www.rexresearch.com/kingmb/MorayKing2017Share.pdf

https://www.osti.gov/scitech/servlets/purl/1338022

http://plasma.fisica.unimi.it/…smi/Rome_Fusione_2017.pdf

https://www.researchgate.net/p…_Properties_collaboration