initiator in boosted fission

[Brainee]

How do boosted fission bombs have fusion fuel in centre since that is where the initiator is?

[exchemist]

5 hours ago, Brainee said:

How do boosted fission bombs have fusion fuel in centre since that is where the initiator is?

They don’t, though, do they? I thought the fusion fuel surrounded the fission fuel that sets it off. 

[Moontanman]

https://en.wikipedia.org/wiki/Thermonuclear_weapon

[MigL]

The Teller-Ulam 'a-ha' moment was realizing that radiation ( x rays ) have pressure, and the pressure produced by a spherically arranged fission explosion is enough to initiate fusion of the fuel inside of it.

[Steve81]

I don’t believe the initiator is in the center (but I’m open to being corrected).

In a modern warhead, the (relatively small amount) of fusion fuel is piped into the pit. Better to store it outside when the nuke is sitting on a shelf, as it makes maintenance easier (tritium decay and all).

The pit is encased in low-sensitivity explosive lenses (polymer bonded explosives as an example), and modern weapons utilize a multi-point initiation system setting off those explosives as a fail safe. Explosives go boom, pit implodes, and the fun begins.

On 5/23/2023 at 3:23 PM, MigL said:

The Teller-Ulam 'a-ha' moment was realizing that radiation ( x rays ) have pressure, and the pressure produced by a spherically arranged fission explosion is enough to initiate fusion of the fuel inside of it.

AFAIK, that was applicable to the second stage of a thermonuclear warhead. They channeled the X-rays down to the second stage which contains far more fusion fuel, and potentially a tamper made of fissile material for even more destruction.

A fun fact for those unfamiliar with it, Tsar Bomba, the largest thermonuclear weapon ever tested, utilized a lead tamper to limit fallout. With a uranium tamper, yield would have supposedly doubled.

[Moontanman]

On 5/22/2023 at 1:58 AM, exchemist said:

They don’t, though, do they? I thought the fusion fuel surrounded the fission fuel that sets it off. 

 

14 hours ago, Steve81 said:

I don’t believe the initiator is in the center (but I’m open to being corrected).

In a modern warhead, the (relatively small amount) of fusion fuel is piped into the pit. Better to store it outside when the nuke is sitting on a shelf, as it makes maintenance easier (tritium decay and all).

The pit is encased in low-sensitivity explosive lenses (polymer bonded explosives as an example), and modern weapons utilize a multi-point initiation system setting off those explosives as a fail safe. Explosives go boom, pit implodes, and the fun begins.

AFAIK, that was applicable to the second stage of a thermonuclear warhead. They channeled the X-rays down to the second stage which contains far more fusion fuel, and potentially a tamper made of fissile material for even more destruction.

A fun fact for those unfamiliar with it, Tsar Bomba, the largest thermonuclear weapon ever tested, utilized a lead tamper to limit fallout. With a uranium tamper, yield would have supposedly doubled.

Here is a link to the design of thermonuclear weapons. 

Quote

The secondary is usually shown as a column of fusion fuel and other components wrapped in many layers. Around the column is first a "pusher-tamper", a heavy layer of uranium-238 (238
U
) or lead that helps compress the fusion fuel (and, in the case of uranium, may eventually undergo fission itself). Inside this is the fusion fuel itself, usually a form of lithium deuteride, which is used because it is easier to weaponize than liquefied tritium/deuterium gas. This dry fuel, when bombarded by neutrons, produces tritium, a heavy isotope of hydrogen that can undergo nuclear fusion, along with the deuterium present in the mixture. (See the article on nuclear fusion for a more detailed technical discussion of fusion reactions.) Inside the layer of fuel is the "spark plug", a hollow column of fissile material (239
Pu
 or 235
U
) often boosted by deuterium gas. The spark plug, when compressed, can itself undergo nuclear fission (because of the shape, it is not a critical mass without compression). The tertiary, if one is present, would

Deuterium and Tritium are used as lithium deuteride instead of solid or gaseous Deuterium and Tritium. 

Quote

Foam plasma mechanism firing sequence.

1. Warhead before firing; primary (fission bomb) at top, secondary (fusion fuel) at bottom, all suspended in polystyrene foam.
2. High-explosive fires in primary, compressing plutonium core into supercriticality and beginning a fission reaction.
3. Fission primary emits X-rays that are scattered along the inside of the casing, irradiating the polystyrene foam.
4. Polystyrene foam becomes plasma, compressing secondary, and plutonium sparkplug begins to fission.
5. Compressed and heated, lithium-6 deuteride fuel produces tritium (³
   H
   ) and begins the fusion reaction. The neutron flux produced causes the ²³⁸
   U
    tamper to fission. A fireball starts to form.

  

[Steve81]

20 minutes ago, Moontanman said:

 

Here is a link to the design of thermonuclear weapons. 

Deuterium and Tritium are used as lithium deuteride instead of solid or gaseous Deuterium and Tritium. 

  

Re: lithium deuteride, that’s only for the second stage AFAIK; given the relative densities, it allows for much more compact thermonuclear weapons like the W80 warhead. I forget the test name where they found out LD would work, but they got a lot bigger bang then they were expecting.

For boosted fission primaries, gas is still used because the amount of gas needed is insignificant and it allows flexibility for dial-a-yield designs. 

Edited August 12, 2023 by Steve81

[toucana]

On 8/12/2023 at 3:27 AM, Steve81 said:

 

A fun fact for those unfamiliar with it, Tsar Bomba, the largest thermonuclear weapon ever tested, utilized a lead tamper to limit fallout. With a uranium tamper, yield would have supposedly doubled.

The Tsar Bomba (Царь-бомба) tested by the Soviet Union on 30 October 1961 had been designed by a team led by Andrei Sakharov to have a theoretical yield of 100 Mt. For test purposes the bomb was deliberately down-rated to a predicted yield of 50 Mt by replacing much of the Uranium-238 tamper with lead.

This was done partly because there were real fears that the TU-95V bomber scheduled to drop the bomb by parachute at 4000m over the Novaya Zemlya peninsula would have been destroyed by the blast from a 100 Mt detonation. The Soviet Union military leaders were also distinctly nervous about proof-firing a 100 Mt weapon over their own territory  because of the radioactive fallout that would ensue.

The test was scheduled to coincide with the 22nd Congress of the Communist Party of the Soviet Union, so they couldn’t take the risk of anything going wrong.

(Footage of the drop)  -