As I promised, text for this week is a brief history of magnetic confinement...
All started in the late 1940s, and the competition was though!
1950s - beginnings
Nuclear fusion research for piece purposes started more-or-less at the same time as Cold War. Hence, most of the research was classified due to a potential military application, as there is the word "nuclear". This was the case until the IAEA Geneva Conference in 1958, where all parties realized that piece-wise and military-wise nuclear fusion are not connected and opened their cards. Scientists really thought that fusion will need only 10-20 years to become a mainstream power source. But, as you now know - this did not happen . . .
1960s - Darwin selection
In the first two decades scientists tried an enormous number of device type, as you can see from the following picture:
Image source: Unknown, many of my professors use it and I cannot find the source link. But the image is super-useful and it would be waste not to use it here...
Open devices were mostly made, due to their easy construction. On the image, you can see 3 branches of pinches and 1 mirror one. And actually, the best score came from θ-pinch, named Scylla.
The popularity of open-devices was short-living as scientists realized that losses at the end are too large. That is why toroidal (closed) side of the MCF-tree is larger. There you can see 4 branches for axisymmetric toroidal devices (tokamak, RFP, FRC and spheromak), 2 for inner ring devices and 2 for the stellarator.
1970s - tokamak
Even though, theoretically (i.e. on the paper) stellarator (a USA machine) is the most promising one - it was extremely difficult to build it, due to the complex magnet shapes. From that reason, the simplest and robust toroidal machine - tokamak - won the race at the end of the 1960s, after the IAEA Conference in Novosibirsk.
Tokamak stands for "toroidal chamber with magnets" in Russian, as it was invented in the Soviet Union. And due to the Cold War politics, Western scientists were very skeptical about tokamak results. That was the reason for UK scientists to go to the Soviet Union and check their claims - the results ended up being even better!
That is the reason why all countries moved from their original devices towards tokamak. The tokamak-booming is best seen here:
Source: my PhD thesis
Tokamak simply makes toroidal magnetic field from the external coils, while the poloidal field is made by the plasma itself - through its current. More details on that are yet to come ;)
1980s - alternatives
Also, you may notice that the number of tokamaks was decreasing after the 1980s - this is because machines started to be larger and more expensive. And oil got a lot cheaper again . . .
People again started to look for different approaches - and best once showed to be the stellarator and reversed-field pinch (RFP). The former one has magnetic fields created completely externally, while the latter one leaves plasma to "do all the job" with the magnetic fields. We see that tokamak is somewhere in between those two principles.
1990 - big success
The biggest tokamak ever was made in 1983 - called Joint European Torus (shorter: JET!). But 14 years passed until JET showed its scientific peak! In 1997 JET created 1.6 megawatts of energy. However, this was not enough for power plant production, as input was over 2 MW... the return was about 60%.
Anyway, this was HUGE success, as JET showed that humans are able to make nuclear fusion on large scale. The science got a big point here, but now it is about engineering to prove that we can make it economical.
Is fusion stagnating?
The standard joke about nuclear fusion is that "it is about 20 years from now", and we are still saying that after 60 years of research. But was there any advance? I will call the image bellow for the third time:
Source: Figure 10.7 from McCracken & Stott, "Fusion - The Energy of Universe"
Here, at the bottom-left, you can see the Soviet tokamak from 1968 - T3, and results of 3 largest tokamaks ever: JET, TFTR, and JT-60U. It is obvious that ion temperature was enlarged a hundred times, while fusion product was improved over a thousand times!!! Such an increase is actually even faster than Moore's law. Also, notice that there is ICF plasma depicted on the photo, and you see that it is lacking for MCF for about one generation of machines.
Unfortunately, since 1997 there was no large improvement as we are all waiting for ITER. But that is a story for another time . . .
If you want to read more details of MCF beginnings and how tokamak succeeded - read my very first post on nuclear fusion.
Next topic: current machines., i.e. present after history.
Please feel free to ask anything in the comments. I will either try to answer you in the comment or even make the new post.