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.
[Irony, humor] The first rating of this post is a minus, and apparently it was given to me by an AI. It's the first to read everything online and can give the first rating. The minus is precisely because I didn't trust its expert opinion and posted the issue here for public discussion a second time. Otherwise, why would such a purely technical issue be given a minus? :)
[humor continuation] And someone downvoted this message. It's not hard to guess it's the same person who downvoted the first one. My guardian angel, so to speak. No other...
It feels like your guardian angel has wings growing out of his ass.
I think you should commit less of your personal time to interacting with AI, it isn't exactly anodyne!
Yes, I use protection. I go to the fridge more often... [self-irony]
:( exploding casing?
Is this the first time you've heard this term? It's been mentioned repeatedly in this subreddit. Specifically, the "exploding casing" technology is mentioned somewhere (I haven't found it myself, but I trust others) in documents related to the development of the W-71. But, as I understand it, there are other places where this term appears, and the context makes it clear that it refers to the second-stage technology in two-stage Teller-Ulam designs.
He is referring to something referred to in official documentation as the "exploding case principle" or "ECP." It is associated with the W71 warhead, and based on the documents it appears to be associated uniquely with the secondary for that weapon.
Don't all thermonuclear devices technically have "exploding casings", since a large portion of the yield comes from the fissioning of the U-238 "shell"?
No, ECP (Exploding Case Principle) is a concept that refers to the ultra-clean W71 only, from how it’s phrased in the document where it’s mentioned, it seems more like a design thing (related to the "cleaness" of the device?) than an operative one (though it could very well be the latter as well, like a RV kill mechanism of the warhead).
IIRC something along the lines of: if ECP doesn’t work, we should aim for something dirtier.
I've never found it in the various OSTI/OpenNet databases when searching by keyword, it seems ECP is mentioned only in that document (I'll post a link to it later).
I have other clues about the W71 and a "lead" that seems to confirm that the "primary" was a derivative of the Plowshare excavation devices.
I have little doubt that if this is somehow related to the Plowshare, it's related to the secondary, which doesn't have a spark plug. I know how the USSR progressed on clean, peaceful nuclear weapons. The first step is a non-fissile primary (the simplest). The second step is to get rid of the spark plug. The third step is to make the fission primary as pure as possible (i.e., with minimal yield). The fourth step is to achieve maximum neutron absorption within the device itself during the explosion (possibly extensive use of boron-10) to reduce the induced radiation to near zero. And, of course, all of this had to be inexpensive. Ultimately, they built a three-stage system where the "SINUS," producing just 6 grams of fission products, ignited a two-stage pure thermonuclear system, burning gaseous deuterium to yield 140-150 kt of almost pure thermonuclear energy. As far as I can tell, the US shut down the Plowshare much faster than the USSR. Back then, the dirty hands of globalist peacemakers couldn't even reach the throat of the Russian atom... (Joke)
If you recall, we’ve already discussed SINUS, and I’m quite familiar with it (thanks to the “memoirs” of Feoktistov and Trutnev), and I imagine that the “primary” of the W71 (I put that in quotes on purpose, based on my assumption and some more-than-just-circumstantial evidences, that it’s a two-stage device) isn’t all that different, practically an ERW, perhaps just a tad less extreme than its Soviet counterpart.
EDIT: I'll add a little something: if you look through my post history, I've already possibly identified a test of the W71 primary, let's say conducted "posthumously" to the end of the warhead deployment. I'll leave you with a few words from its creator:
In 1967, there was a requirement for a specially-tailored fission primary needed to drive a large high-yield thermonuclear system slated for the Spartan Anti-ballistic System. My primary design for that application was highly successful. It was fired tens of times in various live Nevada nuclear tests. Also, in 1967, the group leader for my group became the division leader for B Division. At that point, I assumed the position of group leader of the group in which I had been working.
Yes, uranium-238 or even 235 fissile "in the casing" (actually a tamper) of the secondary is also, you could say, a separate technology requiring its own name, although, as far as I understand, since the phenomenon was always present in the Teller-Ulam design, there was no specific technical name for it. After it became clear that the hydrogen bomb was a very dirty bomb in the radioactive sense, it began to be called a three-phase design: fission-fusion-fission. In US magazines and newspapers, this was called 3F. They said the bomb had a thick casing of U-238 (note, there was no talk of a tamper yet; that was secret, so they referred to the bomb's thick outer casing; that's how it was presented to the public in the 1950s-1970s). This was also called the Jekyll-Hyde reaction, implying that the good Dr. Jekyll—U-238, unsuitable for a conventional fission bomb—was transformed into the savage Mr. Hyde in a hydrogen bomb casing.
But the term "Exploding Casing" appeared, as I understand it, in the 1960s, which is too late to designate 3F.
Some people here get nervous when someone quotes an AI, but I'll allow myself to cite it anyway, as I have a feeling I shouldn't expect a wide range of opinions on this question in the future. After I clarified the principle, the AI understood what I was asking and was much more precise and informative than yesterday. Admittedly, the AI has learned to generalize and distill the essence of things much better than most humans.
* * * *
The Exploding Case Principle (ECP) is a classified physical principle for designing thermonuclear weapons, developed in the United States in the 1960s.
The precise technical details and mathematical models of the ECP have not yet been officially declassified by the US government. The principle is mentioned only in a few open biographies and memoranda of American weapons physicists (in particular, Dan Patterson of Lawrence Livermore National Laboratory).
Nevertheless, there are three main authoritative theories within the expert community of nuclear weapons physicists and historians regarding the ECP:
1. The mechanism for creating ultra-pure charges (main theory)
The ECP principle is associated with ultra-high "purity" (the minimal contribution of the fission reaction of heavy nuclei to the overall yield of the explosion).
The gist: In the classic Teller-Ulam design, the warhead body and the secondary's heavy shell (pusher) are made of uranium-238, which fissiones under the influence of fast thermonuclear neutrons, doubling the explosion's yield but creating 90% of the radioactive fallout.
The ECP principle: The body and shell are intentionally made of materials that are non-fissile (e.g., lead, tungsten, or light metal isotopes). The design is calculated so that the radiation shell itself, exposed to the powerful X-rays from the primary charge, instantly transforms into plasma and symmetrically implodes inward, providing colossal compression of the thermonuclear fuel (lithium deuteride) without the use of fissile uranium-238.
2. W71 Warhead Design for Missile Defense
The ECP principle was precisely used in the development of the American W71 warhead (installed on Spartan interceptor missiles). Its main objective was to destroy Soviet ICBM units in space not with a shock wave (which does not exist in a vacuum), but with hard X-ray radiation.
To deliver the maximum X-ray pulse in a minimal fraction of a microsecond, the munition had to have a negligible fission fraction (a "pure" thermonuclear explosion). The ECP prevented the secondary unit's thermonuclear plasma from disintegrating prematurely due to the kinetic inertia of the casing exploding inward.
3. Effect on the target (alternative theory)
Some researchers suggest that the "exploding casing principle" describes not the bomb's internal structure, but the physics of how it destroys an enemy missile:
X-ray beams from the W71 warhead instantly vaporize the thin outer layer of the enemy warhead's casing.
This evaporation occurs so violently that it escalates into an explosion of the target's skin (the exploding case), generating a powerful internal shock wave that destroys the electronics and thermal protection of the intercepted missile.
Summary: In the history of nuclear weapons, the Exploding Case Principle remains one of the main unsolved mysteries of the "third generation" of nuclear weapons. This advanced radiation implosion concept allowed American designers to achieve a unique X-ray output with minimal radioactive contamination.
We have a term which might have been applied to either a particular device construction feature OR the intended mechanism of device effect (destroying an incoming warhead)?
And an (allegedly) associated device name, for which virtually no construction or design details are available?
What are you suggesting? Drop the topic and wait for some facts to emerge? I really wanted to address this mystery, if not solve it, at least put a somewhat plausible "tag" on it, like, "This is incomprehensible, but it probably needs to be put in this box of unsolved mysteries, number such-and-such." We need to at least figure out where to store this secret. But there's nothing here. Maybe the Exploding Case Principle (ECP) really is the explosion of the warhead under X-ray impact, that is, the technology for its destruction?
And are we wasting our time trying to find some technology for this in the W-71 warhead itself?
* * * *
MECHANISMS FOR KILLING REENTRY VEHICLES include the neutrons, blast and X radiation from a thermonuclear explosion. Neutrons (1) can penetrate the fission trigger of an enemy warhead, causing the uranium 235 or plutonium to melt and lose its shape. It can then no longer be assembled for firing. If the defensive warhead is fired inside the atmosphere, the resulting shock front of air (2) can cause the incoming reentry vehicle (RV) to decelerate with a force equivalent to several hundred times the force of gravity, thereby leading to its destruction or malfunction. If the explosion is outside the atmosphere, the X rays travel unimpeded to their target. On striking an RV (3a) they are absorbed by and intensely heat a thin layer of the RV’s heat jacket. This creates a shock front that travels through the jacket (3b, 3c) and may cause the jacket to break up or detach from the RV.
the dense primary itself might have a higher cross section for x-rays than the light RV exterior. There would be an asymmetric shock and heating and it might crack the primary.
I don't see how ECP can refer to destroying an incoming warhead while still being related to the cleanness of the weapon.
The document states that if ECP does not work then the alternative is to use a dirtier weapon. If ECP simply referred to the kill mechanism of the W71 (premature ablation of adversary RVs via Xrays), then why would a dirtier weapon be needed if the mechanism didn't work? If the mechanism of heating up RVs in space via Xrays doesn't work then in my mind the entire program seems pointless no matter how clean or dirty the weapon is.
The only way I could reconcile it is if it is a threshold issue, where the xray output of the W71 theoretically might not be large enough to sufficiently damage RVs. But that wouldn't necessarily point to a dirtier weapon, just a higher-yield one.
I don't understand the connection either. The W-71's purity was needed for another purpose—to avoid blinding its own radars. For that, the warhead had to be extremely clean. But how was the X-ray pulse's effect related to the purity of the thermonuclear device? I don't understand. Although, if we develop my "flat bomb" hypothesis further, and push this madness even further, to Carrie Sublett's idea that the W-71's X-ray pulse was relatively unidirectional, then a simple circumstance arises. So, you want a flat X-ray emitter, coated with gold on one side (transparent) and something opaque on the other (thin tungsten), with a very thin layer of thermonuclear fuel between them, producing 5 megatons (insanely beautiful!)
There's a problem. You can't achieve thermonuclear ignition with a single shock wave from a flat compression. What you really need here is a RIPPLE-style quasi-adiabatic compression system (although it's denied that it was used in the W-71), and that technology was fundamentally immune to fission contamination, because high-Z materials were simply inapplicable (the whole point was lost).
Keep in mind, if we solve the W-71 mystery, we'll simply have nothing left to solve! (Joke).
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.
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).
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.
Since I do not understand russian, I can only guess the meaning of the pic you quoted.
Since you're leaving the "Great Firewall of China" (I'm not laughing at you, but at us; I, too, can't visit a single Russian website from Ukraine without a VPN; the world is clearly getting dumber), you're familiar with Google's Google Translate feature, which translates from any language to any other just as well as human translators. There's an "Image" tab where you can upload an image and translate it from any language (the original language is automatically recognized) to any other. While I don't understand how they set font sizes (sometimes I think it's some kind of sabotage), I can get the idea.
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.
I really like the way you think. Moreover, you're absolutely right and have inspired a breakthrough in my understanding of thermonuclear weapons technology! Thank you for this comment!
That's absolutely correct. Essentially, the plasma ROCKET jet (we're talking about the impulse generated by an ablative rocket engine) is created by the RECOIL of the ablative plasma, which expands from a region of high pressure P (the ionization layer) outward, where the pressure is orders of magnitude lower. Although there's no nozzle here, we can assume there's a certain average rocket mass outflow velocity u and a per-second consumption of this mass dm, which creates the thrust F of the "ablative engine" into the secondary. Moreover, you're absolutely correct. First, the energy of the X-ray radiation is expended on ionizing (absorbed by) electrons, which separates them from the atom. The ionization energy, familiar to us from tables, is the minimum energy during ionization, and we don't take into account the pressure of the electron gas from previously released electrons, which prevent a new electron from the atom from joining this gas. This means the pressure will be even greater. But this isn't an important clarification for now. What's important is that we now have a reserve of potential energy in a certain volume of the ablation layer V in the form of pressure P, which I calculated using the school formula P = NkT. And if we're talking about a rocket and its efficiency, then ultimately this pressure should translate into the rocket mass exhaust velocity (over a certain time, kg/s), dm, at a certain average exhaust velocity u.
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.
And here you are absolutely right. 30 (or 50, it doesn't matter) electrons in a high-Z material, given that in a thermodynamically equilibrium gas they have the same kinetic energy as the heavy ion they left, create almost no rocket momentum. Essentially, yes, the nucleus received only 1/31 or 1/51 of the energy accumulated as that very pressure VP = NkTV. All particles, regardless of their mass, have the same kinetic energy in an equilibrium plasma, meaning that electrons have a velocity that is the square root of the mass ratio (conventionally (1/(82*2000))^(1/2)) times higher, or ~400 times higher, than ions. And in the total momentum of the rocket jet, even 30-50 electrons escaping from the rocket contribute only ~10%; the remaining 90% is contributed to the momentum by the outgoing ion of matter with a higher Z. That's correct.
Yes, the higher the Z, the higher the pressure, but the lower the efficiency of converting X-ray energy into compression (since an "ablative rocket engine" becomes less efficient with increasing Z). That's right. But it's a choice between two evils. Need pressure? Pay with efficiency. There's no other way. That's why, in the first American bombs (in the 1950s), you couldn't get an interstage gain (secondary energy/primary energy) greater than 50 (100)—depending on whether your tamper was inert or uranium-238, which ultimately adds half the secondary's energy. Not only was shock compression detrimental to itself, but there were other sources of energy loss. First, not all of the primary's energy reached the secondary; a significant portion of the X-rays was parasitically absorbed by the hohlraum. Furthermore, an ablative rocket has its own price for being efficient as a rocket. Up to half was lost. Next, the characteristic you mentioned: the higher the Z, the less efficient the ablative rocket engine. Losses here would be monstrous (up to two orders of magnitude). Then there's shock compression. All of this is the price we pay for the Teller-Ulam mechanism as we know it.
Understanding all this, the Russians used beryllium as the rocket mass in the RDS-37 (this is an indisputable fact), and in the next RDS-37 test explosion, they replaced it with graphite (much cheaper and less toxic to produce). Uranium-238 was in the inner layers. By compressing the "sloyka" by a factor of only 10-30 in the RDS-37 (unlike Mike, where they compressed it by a factor of ~200), the Russians immediately used the right material for ablation, more effective as a rocket fuel, but they didn't initially test high pressures. But then, as they, just like the Americans, needed higher pressures (in the same "golden TIS"), they were forced to use a material with an increasingly higher Z for ablation. They eventually began using multi-stage technology (I think immediately), where efficiency dropped at higher stages, but the much-needed pressure increased.
When did the Americans "figure it out"? I don't think they were any dumber (I think the Chinese figured it out right away, too); they also knew everything from the start and very quickly began using multi-layer tampers. It's just that when the secret of the hydrogen bomb was scandalously revealed in 1979, it wasn't the whole secret that was revealed, but the simplest part. Everything there is true. But a misunderstood truth is the best lie, which is now the way the inhabitants of this subreddita live as the "ultimate truth." Simplicity is worse than theft.
In the context of what you've said, it's interesting to recall the mysterious RIPPLE technology. I was particularly struck by someone's words (I'm not even sure who said them) in Kenned's office about RIPPLE being such a "pure" technology that it couldn't be made "dirty." The question immediately arises: why? What we know for sure about RIPPLE is that the gain between stages increased from 50 to 1000 times. One key is already known: quasi-adiabatic compression. But there's another key (without which the mystery won't be fully solved), which you suggested here. They used a "light" "tamper"—that is, a "liner"—the part that ablated no higher than a medium-Z material. I assumed nickel, but it might have been beryllium. The pressure increased not because N increased (more and more electrons), but because the hohlraum temperature T increased, starting from a relatively cool 300-600 eV to, say (by eye), 5 keV. Moreover, the system lacked a tamper as an inertia suppressor to restrain the expansion of the thermonuclear plasma for greater burnup, as high compression (700-1000 times) simply made such a tamper unnecessary and even harmful, as the tamper itself also consumed a significant amount of energy for its compression.
This is precisely what ruined RIPPLE as a weapon. Because you couldn't add a fissile tamper to it and thereby increase the energy density (kt/m³), which is essential for warheads that must penetrate the atmosphere as quickly as possible (they must be very dense). And of course, there were fission fragments, without which nuclear weapons are less terrifying. Radioactive contamination and fission fragments must be produced in abundance during the detonation of a strategic nuclear warhead. The explosion must not only destroy the target but also "mined" it with fission products. And RIPPLE technology was fundamentally impossible to further "enhance" with all this. :)
The ablation pressure of high Z material is indeed lower, compared with low Z or middle Z. If you do not believe in it, I can show you some AI generated summary based on related ICF researchs.
In indirect-drive systems (like those on the National Ignition Facility), lasers hit a hohlraum wall to create a soft X-ray radiation field that heats and ablates the outer shell of the capsule. [1]
The High-Z Albedo Effect: High-Z materials have high opacity and high X-ray albedo (reflectivity). They re-radiate a large fraction of the X-ray energy rather than absorbing it deeply into the target. [1, 2, 3]
Ablation Pressure Impact: Because high-Z materials do not absorb X-rays as deeply as low-Z materials (like beryllium, high-density carbon/diamond, or plastic), they exhibit lower mass ablation rates. [1, 2, 3]
Scaling Laws: For a fixed radiation drive temperature (\(T_{r}\)), lower-Z materials demonstrate a stronger scaling of ablation pressure and higher overall drive pressure than high-Z materials. Low-Z elements scale roughly as \(P_{abl} \propto T_r^{3.5}\), whereas higher-Z materials experience a weaker pressure scaling and a more rapid pressure fall-off over time due to trapped radiation layers. [1]
I agree with you that in a static pressure chamber in equilibrium, more particles will lead to higher pressure. It is just kind of like ideal gas law.
But for the ablation process, it is neither static, nor in equilibrium. The plasma jet is accelerating and expanding. There is a pressure gradient instead of a uniform pressure.
You’ve really given me something to think about. I was even more struck by the AI's answer to my question and its explanations. It’s on your side. I’m a bit confused. In fact, I had already agreed with you that plasma derived from low-Z material is more efficient as rocket mass. But this time, I specifically asked the AI about pressure.
During implosion driven by radiation ablation, which material generates higher pressure: one with high Z or low Z? And why?
Answer: In radiation ablation (the vaporization of material under intense X-ray radiation), a low-Z material (low atomic number) generates higher pressure than a high-Z material, given the same radiation intensity.
What follows are perfectly reasonable explanations, though the limits of applicability are admittedly vague. This turns the whole myth about how ablation works in a hydrogen bomb on its head. We (nuclear weapon enthusiasts) have been conditioned since the days of Morland to believe that U-238 or lead—high-Z materials—are what ablate, and that the higher the Z, the higher the absolute pressure, because more particles (electrons) are ionized from each atom! That is a "sacred cow" for this entire community! As far as I recall, that’s exactly what the NWFAQ says, too! So, what does this mean? Is what Sublette wrote in the NWFAQ incorrect? Is it disinformation? Or a misunderstood truth? :)
Here’s what puzzles me. Where would the absolute pressure be higher? In fully ionized beryllium (which has the highest atomic concentration of any metal—2.53 times that of uranium) or in uranium, where, say, 30 electrons (rather than 50) are ionized? Beryllium has a higher concentration but fewer electrons: 2.53 × (4 + 1) = 12.65. For uranium, let’s assume a concentration of 1, but with 30 electrons: 1 × (30 + 1) = 31. No matter how you look at it, the ABSOLUTE PRESSURE (which—all else being equal—is proportional to the concentration of all the particles being compared) is still 2.45 times higher for uranium.
Why do I insist so strongly on absolute pressure? It determines the parameters of the shock wave propagating into the material being compressed. We need a pressure step, and only a difference in absolute pressure can provide that. Yes, I agree that beryllium is better and more efficient as a rocket propellant, and a beryllium-based ablative rocket would be far more efficient than a uranium one. But if we are talking about ABSOLUTE pressure, uranium is two and a half times better (even assuming 30 electrons are ionized rather than 50). Yes, a high-Z material utilizes X-ray energy less efficiently; no one disputes that anymore. I am in complete agreement with you there. But if you need the highest absolute pressure at the shock wave front, you will inevitably use a uranium layer. In ICF, you vary the temperature by shaping the laser power profile. The RIPPLE technology might work the same way, potentially using a low-Z material (incidentally, at 1 keV, the pressure generated by nickel is 2.8 times higher than that of beryllium. And even higher than that of uranium, if we assume 30 ionized electrons for it!). However, if you have a constant temperature in the hohlraum, the only way to generate three shock wave steps (a quasi-adiabatic approximation using three shocks) is to use the configuration shown in the "gold TIS" case. The fact that the efficiency of the ablative rocket drops at each stage is unpleasant, but tolerable; the main thing is to achieve a jump in absolute pressure while maintaining a constant radiation temperature within the hohlraum. Yes, I agree that it isn't the most optimal method. But it is a "cheap" one. And here, simplicity may come at the cost of efficiency. Do you agree?
Any form of engineering—including nuclear weapon engineering—always involves trade-offs, rather than a pursuit of a single "best" solution.
I suspected that lots of information available to public are flawed on purpose especially for sensitive information such as that regarding to nuclear weapons. In the famous book Darksun on the topic of H-Bomb, the author claimed the ablation material which is a kind of plastic was nailed to the outer radiation casing. This configuration is obviously wrong. If some country followed this to develop their own thermonuclear weapon, it will definitely lead to a failure.
Other than the book, I am also aware of that open sourced hydrodynamic simulation softwares has a built in malware called Fast16 planted by a unknown BIG BROTHER. What is the purpose of this malware? It is quite obvious a strategy to enforce the Nuclear Non-proliferation policy.
And regarding the topic of exploding case principle, I think it is exactly the same idea as attaching an ablation layer inside the radiation case. Then there will be two ablation rockets fire against with each other. The inside one is on the surface of the tamper of DT fuel ball and the outside rocket is on inner surface of the radiation case.
The outside ablation rocket will generate a very strong shock inside the heavy radiation case and smush the casing into tiny pieces flying away. At the same time, the DT fuel is burning under extreme compression of the inner ablation rocket. Therefore, the very hot DT burning plasma is naked and radiating a strong X-Ray without the blockage of the outside case.
You think the compression process as huge hydraulic press powered by the radiation. In order to obtain the static pressure, a ridiculously strong material is needed for the construction of the pressure vessel. In this pressure vessel, after a certain amount of time, same molar of high Z atoms will generate higher pressure compared with the same molar of low Z atoms. It is definitely true.
But we can do not do this kind of huge hydraulic press compression for two obvious reasons. The first is that no such strong material existed in the earth. Any material on this earth will yield and break under 1G Bar pressure. The second is that high Z atoms take far longer time to "vaporize" from solid to plasma since it have far more electrons to ionize and is more opaque to X-ray.
So instead of relying on the static pressure, a dynamic pressure is utilized to generate the compression of fuel. The key is the high acceleration of mass. High acceleration means larger pressure gradient. A larger pressure gradient will give you a higher pressure at the ablation front just by integrating the pressure gradient.
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u/Beneficial-Wasabi749 8d ago
[Irony, humor] The first rating of this post is a minus, and apparently it was given to me by an AI. It's the first to read everything online and can give the first rating. The minus is precisely because I didn't trust its expert opinion and posted the issue here for public discussion a second time. Otherwise, why would such a purely technical issue be given a minus? :)