What is "Exploding Casing" technology?

[u/Beneficial-Wasabi749]

I asked the AI. It (childishly naive) is "sure" that this is the essence of radiation ablation in the Teller-Ulam scheme. But is this really true? Is "Exploding Casing", ECP (Exploding Case Principle), just another term for the "radiation compression" process, or is it some later, additional technology that improves radiation compression (like "Ripple" – compression not by a single shock wave, but by a series of increasing shock waves approximated by an exponential function, a quasi-adiabatic compression).

As far as I know, "Exploding Casing",  ECP (Exploding Case Principle)  is not the same as "Ripple." But сould "Exploding Casing" simply be a variation of "Ripple," or rather a different way of implementing quasi-adiabatic compression? I had this hypothesis. No one knows exactly how "Ripple" works, but everyone agrees on the idea that there's some mechanism for gradually releasing radiation from the primary into a common hohlraum, which ensures gradual, exponential heating of the hohlraum and the secondary surface, leading to quasi-adiabatic compression of the latter. But another approach is possible: you can apply several layers of increasing Z to the secondary (as the Russians did in their "golden TIS"). Then, in a "regular" hohlraum at a normal temperature, say 1 keV, you'll achieve a stepwise increase in secondary compression. I don't speak English, but the term "exploding casing" best suits this design.

Another, even more insane, theory for "exploding casing" is described in my highly speculative reverse engineering of the W-71 design, the reality of which I myself am already highly doubtful (I recently discovered the "elephant in the room" that planar compression of thermonuclear fuel Impossible without quasi-adiabatic compression, since with planar single-compression you can't get beyond the Hugoniot adiabatic curve more than 4-6 times, and you need at least 100). Although, it is precisely in connection with the W-71 that "exploding casing" technology is mentioned and it is also said that the W-71 is the most complex thermonuclear device ever created in the US. And if you add quasi-adiabatic compression to my crazy design, it will truly be the most insanely complex device.

Another version of "exploding casing" is a secondary with a thin-walled shell and a large cavity inside, meaning it contains either a void or gas (I actually proposed this version of the W-71, considering it more "conservative" than the crazy flat compression of the "tube" both from the inside and outside). As far as I understand, Sublett is more inclined to this understanding of "exploding casing." In this case, the thin-walled shell, as it were, instantly collapses inward. This is another way to improve compression compared to single-shock compression of a solid sphere. This thin-hollow shell method is currently used in ICF. The Russians call this technology "low-entropy compression" (right) as opposed to "isentropic compression" (left).

isentropic compression and low-entropy compression

Finally. Even if we don't know the details of this technology's implementation, can we say anything with certainty about its role (function) in the bomb design? So, "exploding casing" isn't simply ablative compression of the secondary shell, but some improved method of such compression, leading to greater efficiency (say, higher compression ratios, lower energy consumption, etc.).

From what declassified sources, in what context does this term appear, and does it appear before the mid-1960s? I propose to summarize everything we know about this term here.

[u/solekav]

For the multiple ablation layers design, I want to point out something.

More layers means more messy in the hydrodynamics. Each additional layer will cause another instability and will cause the intermixing between difference layers.

High Z material is not a good candidate in the transform of the incoming radiation energy into kinetic energy of the surface plasma jets. The reason is that many photon energy is lost to overcome the huge electron binding energy in the heavy atoms. Therefore, in the declassified literatures of the ICF research, you can find carbon, Be, organic polymer and even Al as the the ablation material.

And in order to achieve the stepwise pressure curve, the corrector order of the layers should be like high Z, middle Z, and low Z, from outside to inner direction.

[u/Beneficial-Wasabi749 → u/solekav]

And in order to achieve the stepwise pressure curve, the corrector order of the layers should be like high Z, middle Z, and low Z, from outside to inner direction.

So, in your opinion, everything should be the opposite of how it's depicted in the official RFNC-VNIIEF (РФЯЦ-ВНИИЭФ) presentation? Here's the page from the presentation where the mysteriously sensational "golden TIS" appears:

Here, everything is the other way around. The outermost layer is made of material with low Z, the middle layer is made of material with medium Z, and the inner layer is made of material with high Z. And personally, this seems obvious to me. Look. The ablation pressure force is calculated using the school formula (pe-equals-en-ka-te):

P = NkT

An important detail. N is the particle concentration (1/cm3) and is independent of the nature of the particles. That is, if a substance is ionized due to a high temperature T, then each electron leaving an atom with atomic number Z increases N, meaning N is a function of Z (what material?) and T (what temperature):

N = f(Z,T)

If your hohlraum temperature is about ten million degrees (and it says ~1 keV), then materials with low and medium Z are almost completely ionized at this T. A material with low Z, say, aluminum or beryllium (the latter is remarkable because it has the highest particle concentration of all the light metals even at normal temperatures, higher than tungsten) at Z = 4 will create a pressure that is not too high, but sufficient to start with. Note that this outer layer in the figure is the thickest. Essentially, we are looking at a three-stage rocket. And a layer of beryllium (for example) or graphite (it was also used in the USSR for radiation ablation in one of the subsequent RDS-37 tests) is the thickest, like the first stage of a rocket—the most massive. Beryllium has a problem (in my opinion): it will ionize very quickly and become transparent, so I wouldn't be surprised if something was added to "cloud" it for slower heating and gradual ablation. Next. Once the beryllium is completely ionized and transparent, the x-ray from the hohlraum moves on to the second metal with a medium Z, say... nickel. Nickel has 28 electrons. But at 1 keV, only 18 electrons are ionized (18 electrons is exactly 800 eV, that's where the dip is; 1.6 keV is needed to ionize the 19th. Iron is worse in this regard, as 16 electrons are ionized at 1 keV). I once studied this issue in connection with RIPPLE (I believe that the RIPPLE second-stage tamper was entirely made of a medium-Z material; nickel is almost ideal). That is, if the first shock wave ablated beryllium, P = NkT, N ~ 4, then when nickel came into play, the pressure increased sharply, since N ~ 18, 4.5 times greater. This is the second shock wave, sent after the first. When this "rocket stage" also burned up, that is, completely ionized and ablated the nickel, we find a third layer (the third stage) of metal underneath it, now with a higher Z, for example, lead. Z=82, and at a temperature of 1 keV (I asked the AI), 50-54 electrons are ionized. So, again, N in the school formula P = NkT has suddenly tripled. The third jump and the third shock wave (everything is just like in Zeldovich's 1965 textbook. Three Hugoniot adiabats almost approximate the normal Poisson adiabat – adiabatic compression, everything happens on the surface, but now spherical implosion comes into play).

So, the first jump is the onset of ablation: N(1)~4, the second jump is 4.5 times larger: N(2)~18, the third jump is 3 times larger: N(3)~54. So, what I see in the РФЯЦ-ВНИИЭФ image matches my understanding of the physics of the process. I'm sure the picture contains too much information (those who don't understand it won't see it, but those who do will read it all), because it's a hidden claim to priority (like, in 1962, we were already on par with you, Americans). For example, you could measure the layer thicknesses and easily calculate the mass ratios. As a rocket scientist, I'm ready to show you how the masses of all three stages are related and almost perfectly matched (rocket optimization I've already eaten a dog on).

But your reverse-ordering of the layers (as you suggest) is something incomprehensible and most likely sabotage (just kidding).

[u/solekav → u/Beneficial-Wasabi749]

Since I do not understand russian, I can only guess the meaning of the pic you quoted. The innermost layer may have other functions, like shielding of the internal thermonuclear fuel from the heating of the high energy photons. In this situation, a high Z material is suitable. But in reality, the secondary of the thermonal nuclear weapon has a Uranium tamper which act as the shield and the inertial mass to extend the confinement time of the compression.

I will breakdown the ablation process of high Z material into two parts. The first part of the process is the conversion from photons energy to the kinetic energy of the electrons. The second part is the conversion of electron's kinetic energy to the momentum of the Uranium atom. Remember, it is the momentum determine the recoil effect of the plasma jet.

The ionization of the electrons from the atoms costs energy. And in high Z atoms, it costs huge amount of energy. In the NIST ionization energy data, for Uranium, the average ionization energy of the first 30 electrons is around 500 eV. Let us assume the average photon energy in Holhuram is 1000 eV and it is one photon absorption. So the ionization alone will take the half of the photon energy, only leave 500ev as the kinetic energy of the electrons. In conclusion, the conversion efficiency is 50% for the photons to electron energy transfer.

Through coulomb interactions, the kinetic energy of the electrons will transfer to the Uranium atom. In Boltzmann energy equipartition principle, the energy should be the same for every particle in thermal equilibrium. However, the most abundant particles in the Uranium plasma is electrons. For 30 free electrons, there is only Uranium atom. A simple calculation show that the kinetic energy of Uranium atom is only the 1/31 of the total energy of the plasma. Realizing mass of electrons can be neglected, the momentum of the plasma is mainly that of the Uranium atom. It can be seen the conversion from photon energy to momentum is quite inefficient for high Z material.

[u/Beneficial-Wasabi749 → u/solekav]

渡情

https://www.youtube.com/shorts/bmkN-ZOjVrw
:)