How the Soviets Got the H-Bomb

I'm joining two meetups next week. Come say hi! Feb 12th at UC Berkeley: www.eventbrite.com/e/asianometry-meet-up-berkeley-… Feb 15th in NYC: partiful.com/e/b3Tpey9enoNpGJT8SLAB

This comment section is full of nuclear physicists.

the H-Bomb layercake route isn't that complicated but it does require having a working nuclear bomb first

Fusion is even harder to kindle than this video suggests. In addition to requiring "a massive amount of energy", the energy must be applied in a very precise way in order to compress the deuterium without excessively heating it, as that would increase the pressure, resisting further compression. To reach and sustain thermonuclear temperatures of billions of degrees, the plasma must be dense enough to be "opaque" to the xrays that are emitted at such temperatures (same mechanism as a space heater, or a lightbulb, but much hotter), meaning that instead of escaping, the xray photons produced by the heat bounce around inside the plasma, keeping it hot. Otherwise the plasma cools off faster than fusion generates heat, which is why Teller's original "super" proposal was non-viable -- simply exploding an atomic bomb next to a container of deuterium is insufficient. Ulam's contribution of radiation-driven implosion was the key innovation, and it took quite a bit of creativity to develop a physical configuration capable of harnessing the energy of an atomic bomb to compress the fusion stage in just the right way. For example, to protect the fusion fuel from premature heating, the design includes a thick uranium shield in front of the secondary that blocks both neutrons and xrays coming from the fission stage. This buys time for fission xrays to travel around the secondary, where their effect on the secondary's tamper creates tremendous implosive pressures of several million atmospheres, an order-of-magnitude more powerful, and thus faster, than an implosion driven by conventional explosives. Around the time the fusion fuel approaches maximum density, a "sparkplug" in the center start to fission, generating heat, and like a match striking dynamite, this triggers a catastrophic rise in temperature and a rapid fusion burning from a configuration dense enough that this process runs to completion within a few nanoseconds, which is quite fast even in the context of an exploding nuclear bomb. The fusion stage compresses and burns to completion before the shockwave from the fission stage can travel the several inches between the two stages. Or really, at such short distances, the fission shockwave is still dominated by radiation energy transport, rather than by the physical motion of the atoms, so in a sense, one can think of the compression of the fusion secondary as being driven by the fission shockwave's interaction with a very specific physical configuration of matter.

17:25 - The first US thermonuclear device was not called the Ivy Mike (That was the name of the test shot) it was called the Sausage device.

The science was never a secret, the engineering was to some degree.

Very informative and well made - and a good choice of topic. One flub: Fermi was the physics Nobel prize winner in 1938. It's a stretch to say that Teller was as "equally famed" as Fermi in Sept 1941.

Richard Rhodes' book, 'Dark Sun,' is a good read on the subject of Soviet bomb/super development, and much more - including Oppenheimer's post war difficulties as depicted in the movie.

Ironic that the Soviet scientists realized early on the viability of combining lithium with deuterium and tritium possibly before the Americans. If American scientists had this awareness it might have prevented the surprise runaway reaction of the Mike Bravo shot

Excellent treatment of a wide range of physics and archival information. Great job - I wish I was around NYC for your meetup.

For the algorithm! Love the video mate, glad to have found your channel. Liked, shared, and subbed. God speed

very well done. thank you for all the work and then sharing.

"That is a problem Tolstoy dealt with in War and Peace. Here you have Napoleon ravaging Europe and now about to invade Russia, and Tolstoy raises this question: Is the leader really a leader, or is he simply the one out in front on a wave? In psychological terms, the leader might be analyzed as the one who perceived what could be achieved and did it." - Campbell, 1986

Another great video! Always a great day when you post one.

14:01 Fission fusion fission Pum-pum :D

A very good video as always, and nearly everything in it is true. But some key parts need to be added or explained more to make the story complete. First, the reason why thermonuclear bomb is so difficult to make and why it took so much research to create it. This reason is not just the high temperature required to ignite the thermonuclear reaction, but a rather more subtle problem. It is mentioned in passing in the video at 16:25 ...*before the heat is dissipated away*. This in fact is the most important thing in the whole story. The intensity of thermal radiation from hot objects increases so rapidly with temperature, that the energy in the "classical super" dissipates from the reaction zone faster than the new energy is added by the fusion. Therefore a self-sustaining thermonuclear reaction is not possible at all. There is no "trigger point", the ignition of a classical super is not possible. It took years of research to establish this fact. So how does the bomb function then? The absolutely key element is the compression of thermonuclear fuel. When the fuel is enormously compressed, to hundreds of times of its normal density, it becomes opaque to its own thermal radiation. This traps the heat and enables the self-sustaining reaction. This was the key discovery which became the basis of 1951 Ulam-Teller radiation implosion patent, which is when the real thermonuclear bomb was born. None of this was understood in 1946 when von Neumann and Fuchs submitted their patent application, so their patent is not considered to be very important. In fact, when British were working on their own thermonuclear weapon after the war, they really struggled to rediscover the idea of compression. And those were the scientists who themselves participated in the Manhattan project in the US! So this idea was very far from obvious even to the extremely knowledgeable people.

It would take another 71 years after Ivy Mike to accomplish, but 3 months ago the laser inertial confinement system at the National Ignition Facility repeated its initial 2022 one-off feat of igniting a fusion capsule in 4 out of 6 more recent attempts. We have now truly entered the era of repeatably achieving the burning plasma regime in the laboratory. This is a HIGHLY nonlinear parameter space, and though the highest yield fusion shots have now produced nearly 4 megajoules (Q factor of ~2), this represents a burnup fraction of only 2% of the hydrogen fuel in the capsule. That means there is further potential for reaching gain factors in excess of 10 or 20 times the laser energy if the ignition and burn wave propagation can be controlled more precisely. these are the brightest neutron sources humans have ever created aside from weapons tests themselves last century.

Radiation implosion was Stanislaw Ulam’s concept. Teller refined it, having finally realised that ‘classical super’ was a total dead end. Oppenheimer, despite his qualms, called it ‘technically sweet’. Hence all fusion weapons, Mike onwards, use Ulam-Teller radiation implosion. In the USSR, Sakharov independently came up with radiation implosion. As did the British, but they obsessed over the more difficult idea of spherical radiation implosion.

This easily could have been an “end of civilizations” video.

Thank you for telling stories like this. From a perspective of a historian and weapons enthusiast, these are some of my favorite videos of yours, I'm hoping you eventually make videos on Pakistan or North Korea's nuclear programs.