The Balloon-man Cometh

General Fusion has made the extraordinary claim that within 12 years (now down to 10?) they will be producing commercial fusion power..."for sure". We have been assured that ‘all evidence’ supports General Fusion’s extraordinary claim. However, the extraordinary evidence required to back up these extraordinary claims has not materialized. As the technology press appears to be only too willing to broadcast these claims uninvestigated, we must look elsewhere for sensible critiques.

In the last episode, inspired by a favorite, ‘70s TV detective, I argued that you don’t have to be a fusion expert to evaluate the claims of a private fusion company. Lieutenant Columbo’s success was predicated on relentless questions, excellent notes, and good old common sense. By the same token, I argue that people from all walks of life can make useful critiques of claims coming out of the fusion 'industry'.

In this episode of Columbo & Friends we will examine General Fusion’s claims from the inexpert perspective of a Party Clown. The fusion energy scheme promoted by General Fusion, Magnetized Target Fusion (or MTF), bears comparison to squishing balloons. First I will explain MTF using the balloon analogy. The Party Clown will be coming later in the article kids....please be patient.

Even a Child Can Understand Magnetize Target Fusion (MTF):?

General Fusion hopes to heat their tokamak-like plasmas by quickly compressing them down to 1/1000th of their original size. If the compression is so fast that there is no heat loss ("adiabatic"), the plasma will heat up. If the plasma is hot enough to begin with, it is possible to reach the extremely high temperatures needed to run a fusion power plant (100,000,000 degrees or more). This should not be disputed.

However, there is the huge matter of that little word “if”. Getting past ‘if’ is precisely why all fusion schemes are hard.

If you quickly compress a regular old party balloon, it too will heat up. In fact, the mathematics for compressing balloons is identical to the math for compressing plasmas. Imagine taking a donut shaped balloon in your hands and compressing it. If you could somehow compress it by 1000x in volume, with no heat loss, the gas inside will heat up to nearly 30,000 C. The math part is easy. The physics is…just a little harder.

That’s Some Party Trick!

You can get an idea of the difficulty of MTF from the balloon analogy. Most of us have played with balloons before. We all know that compressing a regular balloon by a factor of a thousand (1000x) would be a really amazing party trick. Compressing a plasma is a much more impressive trick. It's not like compressing just a regular balloon. More like a greased-up balloon. But not just regular grease. More like electromagnetic grease. What do I mean by ‘electromagnetic grease’? I mean that plasmas are slippery in mind-bending ways. If you want to better understand, go play with some magnets.?

If you bring the north pole of a one magnetic toward the north pole of another magnetic, there is an invisible repulsion. The good news is that this is a way to push something without touching it. This will be necessary for MTF because no physical material can withstand the temperatures needed for fusion. The bad news is that, even in the simple case shown in the video, the repelled magnet does crazy things when you try push on it. This crazy, obstinate behavior is the basis of what I am calling ‘electromagnetic grease’.?

'We got a long story to tell ya...'

Fusion plasmas have internal electric currents. Therefore, they are magnetized (the “M” in MTF). Therefore it is possible to push on a fusion plasma without touching it. But plasmas are like flexible, nested, tubular electromagnets. Like the single magnet in the video, every electromagnet inside the plasma wants to twist and squirm when you push on it. Remember the “bag of rabid weasels” from The Return of the Living Dead?...No? Well, trust me, the squirming bag of weasels situation didn’t go as planned...much like most plans throughout fusion history.

I’ll discuss the unstable (‘rabid weasel’) nature of plasmas in a future article. In this article we focus on the good news. It is possible to push on plasmas without touching them. Useful physics fact: If you approach a magnetized plasma with an electrically conducting surface (like the inside of a collapsing liquid metal vortex), the surface can act like an electromagnetic mirror. The plasma will “see” an image of itself and be repelled. This is why magnets can levitate over superconductors.

If the metal walls collapse on the plasma from all directions, you can get compression and if all goes well, heating! Bob’s your uncle! This is the basic idea behind General Fusion’s approach to Magnetized Target Fusion (MTF). But the proof is in the pudding. After all, fusion has always looked great on paper.?

Send in the Clowns!

What does a balloon artist do if a balloon is leaking? Work fast!! How fast? Much faster than the air is escaping. It's no fun for anyone if the air is gone before the balloon sculpture is finished.

The same idea applies when hoping to compress an MTF plasma to high temperatures. In this case, one must worry about heat leaking out. You must compress the plasma fast. How fast? Much faster than the heat is escaping. Any clown can tell you this.

At an international conference at the end of 2021, General Fusion made the preliminary estimate that their FDP-relevant plasmas lose most of their heat in 3.8 milliseconds. This is formally called the ‘energy confinement time’. A layperson might call it the cooling off period.

Someone Needs a Longer Cooling off Period!

But at that same international conference, General Fusion also reported that they hope to compress their FDP plasmas in 5 milliseconds. Oops! If the plasma cools off faster than the compression, there should be no compressional heating!

Battle Speed vs. Ramming Speed

So how much faster than the cooling off period does the FDP compression have to be? General Fusion published a paper in 2020 that provides a handy equation to calculate this. The model used to derive this equation was presented by General Fusion at an international conference and is explained nicely here.?

To achieve the final temperature of 10 keV from a starting temperature of 0.23 keV, one can calculate that the compression time must be at least 5 times (5x) faster than the energy confinement time, or approximately 0.7 milliseconds. This is very much faster than the published plan. In my previous article we estimated that the Jan 2022 compression milestone on the small prototype was the equivalent of approximately 150 milliseconds when projected to the much larger FDP device.

So, using the best numbers provided by General Fusion and General Fusion’s published equation, we have found that the compression milestone announced in just January of 2022 may well be more than 200x too slow to hope to reach the stated target temperatures in their Fusion Demonstration Plant (FDP). Our Party Clown consultant is very concerned. At Columbo & Friends, we have done our best to inspect the evidence using only the information we could find in the published record. Perhaps we are missing something. Of course General Fusion is vigorously encouraged to lay out a complete analysis for its FDP. The gold standard for this exercise can be found here.??

Is There a Bun in the Oven?

Neither General Fusion, nor any laboratory in the world has performed an adiabatic, 1000x volumetric compression of a tokamak plasma. General Fusion has done a handful of compression tests targeting volumetric compression less than 5x. ?None of those tests successfully demonstrated plasma stability and compressional heating.?

Using published confinement and compression numbers and the same published equation above, General Fusion should not have expected substantial compressional heating in those tests, even if their plasma creatures remain well behaved during the compression.?And the General Fusion authors of that Nuclear Fusion article even mention a very important caveat:

An important requirement for successful MTF is that the plasma remain magnetohydrodynamically (MHD) stable during the compression, since instabilities usually lower the plasma temperature.

And yet, in the compression test which was claimed to have demonstrated compressional heating, the plasm clearly became MHD unstable.

This places an even greater burden of proof on the heating claim. The claim of demonstrated compressional heating is based on a modest increase in neutron production. Does an increased neutron rate constitute a demonstration of compressional heating? ?

Is There a Doctor in the House?

We already know what a bone fide legend of fusion research, Dr. Lyman Spitzer, would say on the matter. But, again, we don’t need a legend of plasma physics to say. Columbo & Friends would like to welcome an obstetrician to the show! Ask any obstetrician if a swollen abdomen constitutes a demonstration of pregnancy? Of course, the answer is “No”. While a rounded belly is consistent with a pregnancy it is consistent with other things as well. Further tests are necessary before making a definitive conclusion.

Similarly, the observation of neutrons in a fusion experiment is consistent with thermonuclear fusion. However, the Zeta fiasco proved long ago that neutrons alone do not constitute a demonstration of thermonuclear fusion. Given the extraordinary nature of General Fusion's claims, their evidence for claiming compressional heating is extraordinarily thin.?

Oh, and just one more thing... Before he leaves, let’s ask our Party Clown another important question. “What’s the worst thing that could happen?”

Pop goes the Weasel!

The worst scenario for a Party Clown is when the balloon sculpture pops before the hopeful eyes of an expectant child. Tokamak plasmas can also ‘pop’. The technical term is a plasma ‘disruption’.?If the ITER & SPARC tokamaks can not mitigate plasma disruptions, the tokamak will lose its title as world champion in the battle for fusion energy.

Sometimes tokamak plasmas spontaneously disrupt while sitting peacefully undisturbed. General Fusion plans to crush their tokamak plasmas down to 1/1000th of their original size. Any clown can tell you which of these two scenarios is more likely to cause the balloon (plasma) to pop (disrupt).?

More Questions Needed!

In this episode of Columbo & Friends we used the commonsense intuition of a Party Clown and an Obstetrician to examine the evidence supporting the General Fusion claim that they are certain to have a commercial power plant by the early 2030’s. The clown is concerned that the plasmas appear to leak out their heat faster than they can be compressed. If so, no heating is expected. The Obstetrician insists that further evidence beyond neutron observations is necessary to conclude that General Fusion has demonstrated compressional heating in their compression tests of small scale plasmas. Both guests are concerned the plasma may well be lost prematurely before it reaches full term (before reaching the required 1000x compression).

Please join Columbo & Friends soon for Episode 2: "Pushing the Envelope" where historians examine the claim that the physics of MTF is ‘inside the envelope’ of the knowledge base established in public fusion research.

In the meantime, don't be shy, KEEP ASKING QUESTIONS!