Need details on certain schemes

Andrew · Senior Member

Need details on certain schemes

GoogleNaut · Guru

They rely on inertial confinement of the plasma--this is what the secondary's pusher/tamper is for. The tamper is composed of a heavy, dense material, usually of fairly high Z (atomic) number like lead or depleted uranium although U-235 has also been used. The outer layers of the tamper are impinged by thermal x-ray emissions filling the 'radiation bottle' containing both the primary and secondary. The thermal x-rays evaporate the outer layers of the tamper; the expansion of this plasma creates a violent shock compressing the rest of the tamper inward. The compression shock initially heats the secondary although not by a whole lot. A plutonium sparkplug is compressed at the center of the fusion secondary and 'fires'--this heats the compressed fusion fuel to ignition temperatures. The dense, compressed tamper holds the fusion fuel in place by its inertia (inertial confinement) until the fusion fuel burns to the point that the compression shock stagnates and reverses direction and becomes an expansion shock. This takes only a few tens of nanoseconds--so it is very, very fast. A fraction of a microsecond.

The secondary's tamper only holds onto the fusion fuel long enough for appreciable fraction, say maybe about 25%, of the fusion fuel undergoes fusion. This is plenty enough to make a very big bang, create a big hole in the ground, and give somebody a really bad day.

For some very, very good information please visit:
http://nuclearweaponarchive.org/

This has some "startlingly" detailed descriptions with supporting mathematics of how Teller-Ulam radiation implosion works.

-- Edited by GoogleNaut at 00:58, 2007-06-09

John · Senior Member

The call it inertial confinement fusion and that is how it is done. The device is basically a cylindrical arraingement. At one end is the primary ... a fission bomb (or other a boosted-fission bomb) and behind is what is called the secondary. It is basically a can made of U-238 filled with lithium-deuteride. The end that faces the primary is particulary thick and is called the pusher. In the center of the secondary is a rod of plutonium called the spark plug. When the primary detonates is releases a flux of x-rays that vaporized metal fillings in foam like material that surrounds the secondary and generates a great pressure to compress the secondary. Neutrons from the primary move through the lithium generating Li6 + n --> T + He4 recations and detonate the spark plug as the pusher compresses the device. In this environment each fusion of D + T yield another neutron. So now we have the plasma.

What contains it is that the main elements of the plasma are of atomic weights 2 through 7 while the container (or tamper) is of weight 238. By conservation of momentum as the lighter particles on the inside bounce off the tamper the latter is moves little as the plasma particle can complete several cycles before it can expand the tamper. It is the interia of the U238 that hold the plasma together so that it can react.

-- Edited by John at 02:00, 2007-06-09

GoogleNaut · Guru

Actually a point of contention: the foam is designed to be as transparent to thermal x-rays as possible. This is why they use polyethylene foam blown with ethane gas. Polystyrene blown with a choroflourocarbon (freon) is too opaque to be useful. Also, the pusher is the cylindrical tamper surounding the cylindrical secondary. The near-trigger endcap is a specially designed shield that deflects some of the primary's blast around the secondary--since only the thermal x-rays is desirable for implosion of the secondary.

The "Holrehm" is a radiation bottle composed of High-Z materials (such as depleted uranium) that contains a good portion of the thermal x-rays inside. The intensify of the x-radiation impinging on the surface of the tamper-pusher is proportional to the volumetric energy density contained within the "Holrehm" or radiation bottle--this implies that a minium sized radiation bottle containing both the primary and secondary is needed (which also coinsides with a minimum weight device anyways!)

The shield is a way to decouple primary blastwaves from the more important thermal x-ray flux from the primary which drives implosion of the secondary.

-- Edited by GoogleNaut at 04:10, 2007-06-09

Andrew · Senior Member

Wow, that is a very good resource, and I'm much more clear regarding the whole thing.

Regarding suns.

Is it as simple as "allot of matter gathers until the point that there is enough temperature and pressure for them to undergo fusion"? Or is there more to it?

10kBq Jaro · Senior Member

Yes, there is more to it.

The media frequently like to say that ITER "seeks to mimic the way the sun produces energy," or "reproducing the sun's power source" (warm & fuzzy image), while NIF & other inertial confinement fusion schemes "simulate fusion reactions that occur in hydrogen bombs" (horror!) -- and of course fission reactors "split atoms, like A-bombs."

In fact, our fusion reactors are very much UNLIKE the sun, in both operating conditions and fuel type, fusion marketing propaganda notwithstanding.

Fusion reactors and the Sun don't even operate on the same physical force, and there aren't any D-D or D-T reactions in the Sun -- both accounting for the fact that the Sun burns for billions of years, instead of blowing up.

The Sun *depends* on reactions using the weak nuclear force, while reactors & bombs use fuels that can be fused quickly & relatively easily using the strong nuclear force only.

In his seminal book "Principles of Stellar Evolution and Nucleosynthesis," Donald Clayton writes concerning p-p fusion that the weak nuclear interaction is so exceedingly rare, that the deuterium (D) that has been formed never actually encounters another D.

As Clayton explains, "after the deuterium has been formed [in the p-p fusion], one could imagine that He-4 might be produced by the reaction D + D --> He-4 + u.

This reaction, however, suffers from..... the fact that the deuterium abundance is kept very small by its interaction with protons [in the reaction D + p --> He-3 + u, following which the helium nuclei fuse according to He-3 + He-3 --> He-4 + p + p ].

.....That these are the major reactions comes about because..... D can build up only to a very small abundance." [ie. two Ds never bump into each other in the sea of protons....]

According to

http://www.shef.ac.uk/uni/academic/N-Q/phys/people/vdhillon/teaching/phy213/phy213_fusion3.html ,
"This [p-p] reaction occurs via the weak nuclear force and the average proton in the Sun will undergo such a reaction approximately once in the lifetime of the Sun, i.e. once every 10 billion years" (the sun's life) ...this in spite of the fact that the protons undergo approximately 10 billion collisions per second with other protons in the solar interior.

John · Senior Member

Googlenaut...thanks for your clarification and that excellent reference. I noticed the comments on that reference about the W78 warhead
http://nuclearweaponarchive.org/Usa/Weapons/W76.html having such a thin case that it was no "thicker than a beer can in places" and that there is concern that any small irregulatities in manufacture could result in it being a dud, i.e. just the primary. I was reading in "Dark Sun" by Richard Roads that in the early Mike test device they used lead as the "radiation bottle" material and of course U238 in the pusher. It would seem that tunsten might also be good for the radiation botton on light weight designs as it is a much stronger material that should be about to hold its in such thin configurations until things nuclear take over. But I'm just guessing. But, I noticed the mention of tungsten in nuclear test in The Book (Project Orion by George Dyson) page 229 that a missile warhead conducted at 250,000 feet.

I just noticed that the Teak test in question was of a developmental ABM warhead and tungsten is used in x-ray devices. Er, most likely the tungsten was used to increase the x-ray output of the explosion for maximium effected on missile RVs heat shielding. Still I can see why that might also work for light weight warheads.

-- Edited by John at 15:52, 2007-06-10

-- Edited by John at 16:41, 2007-06-10

GoogleNaut · Guru

Interestingly enough, things happen so fast and there is so much energy involved that strength of materials don't really matter at all. What does matter is the atomic number of the material and the density. The denser the material the more inertia it has. Higher inertia materials resist acceleration (caused by ablation) than lower density materials. Higher density materials once in motion will impart greater impact forces because of inertia.

A dense tamper material made of lead, tungsten, or depleted uranium (gold would even work!) are essential to compressing and then holding by inertia forces alone the fusion burn in the secondary.

Andrew · Senior Member

How does weak force induce fusion?

John · Senior Member

With the W76 or other ultra-light weight designs is to maintain the correct configuration through all of the process from manufacture to detonation given the minimal design margins. I noted that Freeman Dyson mention to his son that tungsten was used for something in the Teak test which is listed in the reference as an ABM warhead test. We know those exo-atmospheric systems were based on x-ray effect and the tungsten is a key material used in x-ray filliments. I'm guess that they was why of the use of the tungsten in the Teak device as it optimizes the output of x-rays from the devices yield. What I speculating about is might the same material inhance the radiation implosion you have described previously and at the same time preserve the predetonation configuration givent the very tight design tolerances.

Andrew: On your question about how the weak force induces fusion, if you have two protons that collide the consider p --> n + W+ (virtual) --> n + position + neutrino. Since they are so close the engery comes from the eletrostatic energy (to produce the real particles) and so you have a D. But, it this a very low probability interaction since it depends on the weak force, i.e. the W particle.

-- Edited by John at 17:45, 2007-06-10

Andrew · Senior Member

P-P reactions are not dominant from the site linked by 10kBq Jaro. In fact they occur very rarely throughout the Sun's lifetime.

What I want to know is, does the dominant reactions in the sun are induced by sheer pressure and gravity?

John · Senior Member

They occur rarely for each proton but they are the basis of the sun fuel cycle. There are a lot of protons in the mix and the one deeper in the sun aren't under the average conditions either. Gravity is the basis of the suns confinement system. With the gravity and pressure also comes temperature.

-- Edited by John at 21:12, 2007-06-10

Andrew · Senior Member

All right, that's what I thought it worked on.

Could you please do a fact check on what I want to list?

Suns (or as I prefer them: oversized fusion lightbulbs):
Confinement: gravity and sheer mass
Coloumb-overcoming force: temperature
Temperature source: sheer gravity trough mass and pressure (and friction and collisions coming from them)
Fuels intended to use: varies by sun type, general answer is all
Description: In outer space, clouds of various elements eventually gather up. Hydrogen being the most common element, hydrogen gathers up the most. Once this process gathers up a stellar mass-worth of matter, gravity from the gathered mass will create enormous pressure and friction. Enough to create plasma and start atoms to fuse. Fusion will further heat any matter in the core, thus further inducing fusion until elements that are too difficult to fuse are accumulated.
Status of verification: go outside at day and look for yourself :)

H-bombs of the Teller-Ulam kind
Confinement: inertial trough x-rays
Coloumb-overcoming force: ionizing photons
Source of force: an uranium or plutonium bomb
Fuels intended to use: D-T and D-D combined
Description: X-rays from a fission bombs are used to heat up and ionize the fuel materials that are contained in a cylinder container. Within the centre of the cylinder, there is a tube of plutonium. A fission reaction is induced by shock-waves caused by the x-rays. This causes the fuels to be confined by two sides, more then enough for them to undergo fusion. Once fusion reactions are started, they will trigger further fusion reactions by neutrons.
Status of verification: Successful tests under the name Ivy Mike (1 November 1952) and more. Service in military to this day.

Tokamaks
Confinement: magnetic
Coloumb-overcoming force: temperature
Sour of temperature: varies
Fuel intended to use: D-T, experiments with D-D
Description: Using very strong magnets in a toroidal shape, gas is heated to plasma temperatures, after which it is accelerated by magnetic fields. Fusion undergoes when temperatures are high enough for colliding ions to fuse.
Status of verification: Tokamaks are verified in experiments, however no tokamak to this date has archived breakeven, and it is questionable if they will ever will or become practical.

I also want to describe Farnsworth-Hirch fusor and Polywell, and maybe supernovas too. I'm tired now.

GoogleNaut · Guru

I think the tungsten was also used as part of the ABM warhead's heatsink nosecone--thus the radiation bottle was also the aeroshell--an efficient weight reducing feature.

The production of x-rays is not enhanced by the presence of tungsten but only in the sense that it is a high "Z" material--that is all. X-rays are produced from deep electron-shell interactions with high proton-count nucleii. Since this is so, then any material with deep enough electron shells will suffice for x-ray production.

The fact that almost all filaments are made from tungsten has more to do with the fact that it has a very high melting point--so a filament in an x-ray tube will almost certainly thus be made of tungsten. The target for the cathode rays--the electrons 'boiled off' from the filament--must be heat resistant for long life, and must also be a high-Z material for efficient production of x-rays--and the fact that tungsten is already present at the manufacturing plant pretty much guarantees the use of tungsten for the target.

John · Senior Member

Ok, but are the high Z elements equal in their x-ray properties? Chuck Hansen in his book "U.S. Nuclear Weapons" states in reference to the W-71 device which was the warhead for the Spartan interceptor: "The W-71 used a layer of gold around its secondary to enhance fusion and maximize x-ray output". It seem that there most be something special about the gold or they wouldn't have chosen such an expensive material.

I think the tungsten was also used as part of the ABM warhead's heatsink nosecone--thus the radiation bottle was also the aeroshell--an efficient weight reducing feature.

That is an interesting point. On a somewhat different point is the great reduction in fission bomb weights by replacing their depleted uranium reflectors with ones made of beryllium.

-- Edited by John at 05:24, 2007-06-11

GoogleNaut · Guru

I'll bet my bottom dollar the gold had nothing really to do with xray output--but was instead used to partially decouple thermal emissions from the inside of the heat-shield aeroshell to the warhead inside. Going further, it probably wasn't all gold, but probably a thin gold coated molybdenum film, kind of a high temperature mylar film for thermal insulation. A thin layer of gold isn't going to improve thermal x-ray emissions that much--but a thicker radiation case/aeroshell would...

No, not every high Z-number substance is created equal--however inside a weapons case that intensity of thermal x-rays is high enough that this will probably overwhelm any variance from one material to the next. As long as it has a relatively high Z-number, then it ought to work just fine.

John · Senior Member

Are you saying that all thermonuclear warhead of a given yield are about the same for producing X-rays? It seems to me that there has always been the claim or perhaps mythology that the old style exo-atmospheric ABM warheads produced an enhanced X-ray output. Perhaps this is just the result of a space explosion of a nuclear bomb.

On the other hand there are references to other possibilities in the public literature. In the Orion book by Dyson's son George his father is comfortable talking about the tungsten from a fallout point of view but won't (because of classification?) say why it was present in the test device. Also there is reference to the Orion propulsion charges have a renewed significance in the 1980s SDI. Don't forget the Teller Excaliber concept during the SDI program that was a nuclear driven X-ray laser.

GoogleNaut · Guru

The old ABM warheads for the Sartan missile, deactivated in 1972, had a 5 Megaton thermonuclear warhead. X-ray output for these things are what is called "thermal x-rays." What this means is that the x-rays are emitted as a direct result of blackbody emission from the fission/fusion fireball--usually the heated plasma from vaporized tamper and Hohlraum (radiation bottle) debris. As such, the spectrum of emitted radiation is almost entirely dependent upon the temperature of the (and the degree of ionization) of the resultant fireball. I'll see if I can locate the actual equation which describes this spectrum--it is quite interesting because it duplicates the 'colors' of radiation emitted by a heated blackbody. The fireball in the case of a nuclear explosion is so hot that it glows beyond 'white hot' or 'ultraviolet hot" but 'x-ray hot' for want of a better term. The peak of the radiated energy lies within the x-ray part of the spectrum--and this has direct consequences for all of the other weapons effects that we will observe.

The temperature of the fireball is a function of the density of the energy release within that fireball. This is why a thermonuclear explosion generates 'enhanced' xray output over an ordinary 'fission' explosion. The total energy release (and approximate volumetric energy release) in the case of the W-71 Spartan warhead is roughly 500 times the energy release of the likely primary yield (say about 10 kt,) so the temperature of the resultant initial fireball is much, much hotter. This is the origin of the 'enhanced x-ray output.' And other than W-71 having a fusion secondary, there really isn't anything particularly technologically special about the ABM warhead.

http://en.wikipedia.org/wiki/LIM-49A_Spartan

10kBq Jaro · Senior Member

GoogleNaut wrote:
The old ABM warheads for the Sartan missile, deactivated in 1972, had a 5 Megaton thermonuclear warhead.

The total energy release (and approximate volumetric energy release) in the case of the W-71 Spartan warhead is roughly 500 times the energy release of the likely primary yield (say about 10 kt,)

I would think that anything with such a huge fusion-to-fission yield ratio would radiate most of its energy in the form of fast neutrons.

Unless of course that 5 Mt yield of the secondary is mostly from NU fission, induced by fusion neutrons, rather than just fusion.

John · Senior Member

I would think that anything with such a huge fusion-to-fission yield ratio would radiate most of its energy in the form of fast neutrons.
That's an interesting point. If Googlenaut is right it most likely would have a U238 tamper and would get a lot of yield from the ultra-fast neutron fission.

GoogleNaut · Guru

I am almost certain--now that you mention it--that fission-fusion-fission was the mechanism for the Spartan W-71 warhead. A relatively heavy secondary tamper made from U-238 would have provided an excellent target for the fast neutrons and would have fissioned an appriciable amount of this material. As much as half of the total warhead yield may be generated from the final fission stage--a very significant amount. Also, the weapons case would have provided an excellent medium to transfer this very high intensity thermal x-ray flux to the surrounding air. Absorbtion of this x-ray flux is the primary mechanism for the creation of the 'luminous' fireball typically seen--the initial luminous fireball for the W-71 may have been as much two miles in diameter! Any missile within that radius would likely be 'killed' by the intense thermal x-ray flux within this fireball.

Interestingly enough, one may think that this mechanism results in instant and complete vaporization of the target. Not necessarily so--only objects within say 500 m or so of the detonation point may experience near total vaporization as the x-ray flux penetrates through and saturates the target. More distant 'kills' can still be accomplished as the x-ray flux vaporizes material on the surface of the object--ablating a thin surface layer of material. The 'ablation shock' that is created then travels through things like heatshields and bulkheads, causing mechanical spalling or surface fracturing of the material on the other side as the shockwave is reflected from the inside surface. This spalling of material will send fragments like bullets showering through the inside of whatever was hit--this internal 'shot gun blast' is what actually destroys the delicate mechanisms inside whatever was hit--like a ballistic missile warhead for instance.