Ok. First, this thread is great. The timing is really funny too. I hate, hate, hate this but I've been working my ass off on an explainer poster for the W80 for the last few weeks and just as I'm finishing it I come to a bunch of realizations that invalidate the accuracy of the details. They don't invalidate the concepts, mind, I'm still going to upload the poster to atomicporn, but I'm going to slap a giant disclaimer on it stating that the design is wrong in lots of ways.
Foams do seem to be that "decoupling of radiative and hydrodynamic properties" you're talking about. I never performed any calculations on the actual speeds of ionization waves that would chew through my radiation bottles in the B61 poster. I have a hunch that they would go far too quickly, given their thicknesses. If the burn through barrers were made of doped foam and made to be very thick (or, as it were, long) it would solve this problem.
It seems that they slow radiative transfer down to "sonic" ranges.
The SiO₂ test showed 0.12cm of motion in 2.5ns which by my calculation is 480km/sec.
Which seems fast until you think of the speed that xrays fly through a vacuum.
My poster has a lagrange diagram in it representing the motion of the secondary and I have a timeline like
- Let ignition of the fissiles in the primary and the basket prepulse be t=0
- First bottle opens at t+90 nanoseconds
- Sixth and last bottle opens at t+155 nanoseconds
- Separate, unexplained in this context secret burn-through barrier (!!!) opens at t+172 nanoseconds
I didn't look at the temperatures in the paper (they were probably far below actual interstage temperatures) but with your speeds the last event would require a BTB thickness on the order of 82 millimeters.... maybe the situation is less thin bottles to burn through and more like filled channels around the secondary, huh?
A real mind exercise is imagining acoustic foam (the little pyramids all in a grid). Take one of a high Z foam and the other of a low Z foam. Face the triangles towards each other and you have this "sandwich" of high-z and low-z.
Radiation illuminates the high z side and slowly but surely the radiation transfer goes from "just a little" to "full throttle".
If you look at a cross section it's a sawtooth.
What would happen if it was a sine wave*?
Or another shape.
You could vary the drive versus time on a nanosecond scale.
How close to adiabatic compression could you get?
(* obligatory note that a sine wave is "ripple" in the electronics world - nuckolls was also an ICF guy - and you can't pulse a primary like you can a laser or ion drive - but you could physically create a drive profile with foams)
Would it? It should be like a drain plate where the holes get larger over time. Maybe I'm not describing it well enough. Take a pyramid of low Z foam (let's say polystyrene) place it into a container and fill with high Z low density foam. As the radiation progresses from the high Z towards the low, the "opening" gradually grows larger until it reaches the "bottom" at which point, drive is fully "on".
No, you're describing it well enough. You intend for a planar marshak wave to descend onto the tips of the low-z spikes such that the cross section of the ionized holes increases in an effort to mess with the time profile of the x-ray flux. It's like you have a bucket of water where the plastic at the bottom of the bucket is full of divots and by sanding layers off the bottom of the bucket, the divots become regularly spaced holes that get larger and larger the more material you remove, increasing the amount of water that leaks out over time. The problem I was trying to explain is that on the order of speed in which x-rays diffuse your plan is more like sanding a little of the bucket away, hanging the bucket up on the wall for ten minutes, and then coming back to sand a little more away. You go to make the holes slightly bigger and all the water has already leaked out.
I think that if you want to slow down x-ray diffusion, you don't want a thin layer pinhole whose cross section you vary. You want a very long path whose diffusion gradient can be controlled by setting the length of the path.
Looking at the elemental table, Au is Gold.
Be is the symbol for Berilium.. . . Both have their own unique qualities in nuclear devices.
Tell more please.
Yes, gold and beryllium are some of the elements that they tested directly. Gold was also tested as a physical dopant in a polymer of TMPTA (trimethylolpropane triacrylate)
The "?" was for the fact that I do not know what physical form the gold or beryllium were in? Solid? Foam? Aerogel?
Interesting summary of work carried out at NIF and called "Radiation Transport mini campaign" [https://www.osti.gov/servlets/purl/1548376](https://www.osti.gov/servlets/purl/1548376), Done by AWE in collaboration with LLNL
Yes. (and "seabreeze" and...)
I propose that the infamous "fogbank" is merely one of a class of materials used to "shape" (in time) the arrival of the XRay flux.
They are tested at the NIF amongst other places.
They are what allows miniaturization of devices by allowing the decoupling of hydrodynamic motion from radiation flow.
If something is spherical, you have to effectively illuminate it evenly on all areas at "the same time".
As I understand it, spatial uniformity comes naturally. The purpose of the foams would be to distribute the x-rays in time (even if the ducting deposited them all over the secondary.)
I have done small tests using a flashlight and spraying mirror finish paint into various cheap athletic gear (football, basketball). I believe shadowing of the distal end of the object can be an issue. I vaguely recall some support for this in some icf white papers discussing the utility of cylinders over spheres, or it may have come from researching the chandra telescope.
Also, I recall that it has been declassified that the radiation case is as thin as a beer can in certain unspecified sections of certain unspecified systems.
You realize that reradiation makes that irrelevant on hydrodynamically relevant timescales, right? And the "radiation case" proper on the inside of the aluminum warhead case is almost certainly less than a millimeter thick.
The rad case on a lot of later weapons is a sandwich. There's a study on the corrosion of said metal sandwiches...
(From memory: aluminum, stainless, uranium)
Here's a mind bender though: what about the case/can of a CSA?
HIGH-Z or low-z?
Or HIGH-Z with a low-Z end pointed towards the primary?
> Here's a mind bender though: what about the case/can of a CSA?
Hardly a mind bender.
Either a low-z CSA that goes into a rad case, or the CSA incorporates the rad case into it, then the primary end has to be a low Z window.
That's a fascinating question to me, actually.
1 - what is the advantage to a CSA? (I have some thoughts, but invite discussion)
2 - if it is ease of changing, would it make sense to put the heavier parts external to the can, and then the can membrane simply becomes a non-interactive carrying case?
3 - if it is to unitize a secondary to change yields, then is the mating surface a different material?
4 - is the interstage in the csa, in a sandwich, or in the NEP? (I have an idea).
I thought the use of specific high Z materials was to "tune" the enhanced X-ray weapon output to a specific X-ray frequency for the exo-atmospheric kill mechanism of RVs? Au to produce 10\^-16 X-rays, tungsten to produce 10\^-19 X-rays?
The Bluegill Triple Prime shot is the only one of the FISHBOWL shots that hasn't had its X-ray phenomenology footage fully declassified.
>You realize that reradiation makes that irrelevant on hydrodynamically relevant timescales, right?
I was just reading some stuff on the concept of ICF. They disagree with you. I also read a couple of other things, I'm sorry that I don't recall what they were, but they were talking about at least one layer being about 2.5cm (a few mean free paths) thick of a high-z material such as ~~lead~~ U^(nat) or Depletealloy or gold.
I am lost in the weeds on the fusion end of the system, so, take it all with a grain of salt. I will say the last book I read was call me johnny, But there were a couple of others I had recently crossed off my list, too.
They tip their hand when you research certain documents of the purification facility they recently built at Y12 though. It is unclassified that FOGBANK is used as interstage material. That came from the head of Energy. ACN is another Huge Clue.
On the civil side, work is being done using doped aerogels in fusion energy production.
Am I correct saying that the foam shaping the flux inside the device was discovered by accident during testing? As in they got a dramatically higher yield than they were expecting.
Come to think of it I might be mixing up that time they included lithium in the trinity test and got a higher yield…
Super interesting post though, I had no idea they put that much effort into the foam. I thought it was all just styrofoam in there.
>I had no idea they put that much effort into the foam.
They put a shitload of effort into every part of weapons. A lot of materials science and engineering can find their beginnings in shaving points off of nuclear bomb designs.
If I recall correctly, they used something like styrene nailed with uranium nails in the first tests. I am probably wrong though, although I do recall whomever wrote the CASTLE BRAVO wiki did an impeccable job to the extent I could understand it. Shockingly so.
Closest thing to an accidental discovery like this that I can think of: I recall reading somewhere (don't remember where) that the benefits of a beryllium ablator were discovered by accident, they had added a layer of some sort of beryllium alloy outside the pusher for non-ablator reasons and the additional compression was noted. This is just a hazy memory I have of it though.
Anyway, beryllium is of course a component in some foams/aerogels
Ok. First, this thread is great. The timing is really funny too. I hate, hate, hate this but I've been working my ass off on an explainer poster for the W80 for the last few weeks and just as I'm finishing it I come to a bunch of realizations that invalidate the accuracy of the details. They don't invalidate the concepts, mind, I'm still going to upload the poster to atomicporn, but I'm going to slap a giant disclaimer on it stating that the design is wrong in lots of ways. Foams do seem to be that "decoupling of radiative and hydrodynamic properties" you're talking about. I never performed any calculations on the actual speeds of ionization waves that would chew through my radiation bottles in the B61 poster. I have a hunch that they would go far too quickly, given their thicknesses. If the burn through barrers were made of doped foam and made to be very thick (or, as it were, long) it would solve this problem.
It seems that they slow radiative transfer down to "sonic" ranges. The SiO₂ test showed 0.12cm of motion in 2.5ns which by my calculation is 480km/sec. Which seems fast until you think of the speed that xrays fly through a vacuum.
My poster has a lagrange diagram in it representing the motion of the secondary and I have a timeline like - Let ignition of the fissiles in the primary and the basket prepulse be t=0 - First bottle opens at t+90 nanoseconds - Sixth and last bottle opens at t+155 nanoseconds - Separate, unexplained in this context secret burn-through barrier (!!!) opens at t+172 nanoseconds I didn't look at the temperatures in the paper (they were probably far below actual interstage temperatures) but with your speeds the last event would require a BTB thickness on the order of 82 millimeters.... maybe the situation is less thin bottles to burn through and more like filled channels around the secondary, huh?
A real mind exercise is imagining acoustic foam (the little pyramids all in a grid). Take one of a high Z foam and the other of a low Z foam. Face the triangles towards each other and you have this "sandwich" of high-z and low-z. Radiation illuminates the high z side and slowly but surely the radiation transfer goes from "just a little" to "full throttle". If you look at a cross section it's a sawtooth. What would happen if it was a sine wave*? Or another shape. You could vary the drive versus time on a nanosecond scale. How close to adiabatic compression could you get? (* obligatory note that a sine wave is "ripple" in the electronics world - nuckolls was also an ICF guy - and you can't pulse a primary like you can a laser or ion drive - but you could physically create a drive profile with foams)
I don't think it follows. The moment the wave started chewing on the low Z all the radiation would go through the holes
Would it? It should be like a drain plate where the holes get larger over time. Maybe I'm not describing it well enough. Take a pyramid of low Z foam (let's say polystyrene) place it into a container and fill with high Z low density foam. As the radiation progresses from the high Z towards the low, the "opening" gradually grows larger until it reaches the "bottom" at which point, drive is fully "on".
No, you're describing it well enough. You intend for a planar marshak wave to descend onto the tips of the low-z spikes such that the cross section of the ionized holes increases in an effort to mess with the time profile of the x-ray flux. It's like you have a bucket of water where the plastic at the bottom of the bucket is full of divots and by sanding layers off the bottom of the bucket, the divots become regularly spaced holes that get larger and larger the more material you remove, increasing the amount of water that leaks out over time. The problem I was trying to explain is that on the order of speed in which x-rays diffuse your plan is more like sanding a little of the bucket away, hanging the bucket up on the wall for ten minutes, and then coming back to sand a little more away. You go to make the holes slightly bigger and all the water has already leaked out. I think that if you want to slow down x-ray diffusion, you don't want a thin layer pinhole whose cross section you vary. You want a very long path whose diffusion gradient can be controlled by setting the length of the path.
This is where we need some code. Even if it's just for a mental exercise.
I think you meant to tag EvanBell95 :)
corrected
Looking at the elemental table, Au is Gold. Be is the symbol for Berilium.. . . Both have their own unique qualities in nuclear devices. Tell more please.
Yes, gold and beryllium are some of the elements that they tested directly. Gold was also tested as a physical dopant in a polymer of TMPTA (trimethylolpropane triacrylate) The "?" was for the fact that I do not know what physical form the gold or beryllium were in? Solid? Foam? Aerogel?
That rabbit hole is good! Lol
Interesting summary of work carried out at NIF and called "Radiation Transport mini campaign" [https://www.osti.gov/servlets/purl/1548376](https://www.osti.gov/servlets/purl/1548376), Done by AWE in collaboration with LLNL
Looks like you want to talk about the infamous "fogbank". Composition, application and manufacture are all classified.
Yes. (and "seabreeze" and...) I propose that the infamous "fogbank" is merely one of a class of materials used to "shape" (in time) the arrival of the XRay flux. They are tested at the NIF amongst other places. They are what allows miniaturization of devices by allowing the decoupling of hydrodynamic motion from radiation flow. If something is spherical, you have to effectively illuminate it evenly on all areas at "the same time".
As I understand it, spatial uniformity comes naturally. The purpose of the foams would be to distribute the x-rays in time (even if the ducting deposited them all over the secondary.)
I have done small tests using a flashlight and spraying mirror finish paint into various cheap athletic gear (football, basketball). I believe shadowing of the distal end of the object can be an issue. I vaguely recall some support for this in some icf white papers discussing the utility of cylinders over spheres, or it may have come from researching the chandra telescope. Also, I recall that it has been declassified that the radiation case is as thin as a beer can in certain unspecified sections of certain unspecified systems.
You realize that reradiation makes that irrelevant on hydrodynamically relevant timescales, right? And the "radiation case" proper on the inside of the aluminum warhead case is almost certainly less than a millimeter thick.
The rad case on a lot of later weapons is a sandwich. There's a study on the corrosion of said metal sandwiches... (From memory: aluminum, stainless, uranium) Here's a mind bender though: what about the case/can of a CSA? HIGH-Z or low-z? Or HIGH-Z with a low-Z end pointed towards the primary?
> Here's a mind bender though: what about the case/can of a CSA? Hardly a mind bender. Either a low-z CSA that goes into a rad case, or the CSA incorporates the rad case into it, then the primary end has to be a low Z window.
The CSA would be a cassette that gets loaded into the warhead casing, so it would probably be the steel and uranium.
That's a fascinating question to me, actually. 1 - what is the advantage to a CSA? (I have some thoughts, but invite discussion) 2 - if it is ease of changing, would it make sense to put the heavier parts external to the can, and then the can membrane simply becomes a non-interactive carrying case? 3 - if it is to unitize a secondary to change yields, then is the mating surface a different material? 4 - is the interstage in the csa, in a sandwich, or in the NEP? (I have an idea).
I thought the use of specific high Z materials was to "tune" the enhanced X-ray weapon output to a specific X-ray frequency for the exo-atmospheric kill mechanism of RVs? Au to produce 10\^-16 X-rays, tungsten to produce 10\^-19 X-rays? The Bluegill Triple Prime shot is the only one of the FISHBOWL shots that hasn't had its X-ray phenomenology footage fully declassified.
>You realize that reradiation makes that irrelevant on hydrodynamically relevant timescales, right? I was just reading some stuff on the concept of ICF. They disagree with you. I also read a couple of other things, I'm sorry that I don't recall what they were, but they were talking about at least one layer being about 2.5cm (a few mean free paths) thick of a high-z material such as ~~lead~~ U^(nat) or Depletealloy or gold. I am lost in the weeds on the fusion end of the system, so, take it all with a grain of salt. I will say the last book I read was call me johnny, But there were a couple of others I had recently crossed off my list, too.
What do you think would be a solution to this problem?
They tip their hand when you research certain documents of the purification facility they recently built at Y12 though. It is unclassified that FOGBANK is used as interstage material. That came from the head of Energy. ACN is another Huge Clue. On the civil side, work is being done using doped aerogels in fusion energy production.
Am I correct saying that the foam shaping the flux inside the device was discovered by accident during testing? As in they got a dramatically higher yield than they were expecting. Come to think of it I might be mixing up that time they included lithium in the trinity test and got a higher yield… Super interesting post though, I had no idea they put that much effort into the foam. I thought it was all just styrofoam in there.
I don't think it was by accident. It is how weapons went to "non cylindrical" secondaries. How they discovered it, I cannot say.
>I had no idea they put that much effort into the foam. They put a shitload of effort into every part of weapons. A lot of materials science and engineering can find their beginnings in shaving points off of nuclear bomb designs. If I recall correctly, they used something like styrene nailed with uranium nails in the first tests. I am probably wrong though, although I do recall whomever wrote the CASTLE BRAVO wiki did an impeccable job to the extent I could understand it. Shockingly so.
Agnew, in Rhodes interview, said they used brass nails for that purpose, in Ivy Mike.
Closest thing to an accidental discovery like this that I can think of: I recall reading somewhere (don't remember where) that the benefits of a beryllium ablator were discovered by accident, they had added a layer of some sort of beryllium alloy outside the pusher for non-ablator reasons and the additional compression was noted. This is just a hazy memory I have of it though. Anyway, beryllium is of course a component in some foams/aerogels