Halite / Centurion and fission - fusion power plants

[BWV]

Its unclear to me what exactly these tests entailed and how much today is still top secret. They involved inertial confinement fusion with x-rays from a fission explosion.

never see this discussed - forgetting about political issues with fission, how feasible is a fusion reactor utilizing fission (analogous to an h-bomb)?

is it known what the x-ray mechanism from Halite / Centurion was? Simply a mini H-Bomb or were the x-rays from the fission reaction used more like lasers in current inertial confinement reactors?

 

[berkeman]

Its unclear to me what exactly these tests entailed and how much today is still top secret. They involved inertial confinement fusion with x-rays from a fission explosion.

never see this discussed - forgetting about political issues with fission, how feasible is a fusion reactor utilizing fission (analogous to an h-bomb)?

is it known what the x-ray mechanism from Halite / Centurion was? Simply a mini H-Bomb or were the x-rays from the fission reaction used more like lasers in current inertial confinement reactors?

Links? Or are those top secret too?

 

[BWV]

I’d post them, but then I would have to kill you ;)

Seriously, not much. Mentioned in the recent boom Star Builders

found this

https://nuke.fas.org/cochran/nuc_11309401a_135.pdf

https://www.science.org/doi/abs/10.1126/science.233.4770.1256

https://www.nytimes.com/1988/03/21/...-fusion-spurs-a-dispute-among-scientists.html

 

[Alex A]

All IMHO.

Most of the energy released from a fission stage is in the form of soft X-rays. I don't remember where I read this.

Funneling these with low Z channels makes it behave more like a gas and using this to compress fuel to ignition is traditional H-bomb engineering. If you can do it with a thermonuclear fuel pellet, you can do it with the second stage of a weapon.

(Now moving into wild speculation) some of the tests could even have been just an existing weapon design without a spark plug or fissionable outer casing.

 

[mfb]

Exploding nuclear weapons underground to heat a huge amount of material (water or whatever) has been proposed as a power plant design, but the radiation and safety concerns don't make this practical.

 

[Astronuc]

Its unclear to me what exactly these tests entailed and how much today is still top secret. They involved inertial confinement fusion with x-rays from a fission explosion.

Details of nuclear weapons tests are held secret.

how feasible is a fusion reactor utilizing fission (analogous to an h-bomb)?

Not feasible. The energy is release in microseconds, which produces high pressure shock waves which tend to disrupt solid materials, besides the fact that it is difficult to transform dense thermal energy into useful mechanical/electrical energy. If one does the calculations, the release of thermal energy from a detonated nuclear device requires a small amount of mass, much less than that which is required to exceed criticality, so the proposed process would be inherently inefficient, in addition to having the complication of fission products and transuranic radioisotopes dispersed in the system.

is it known what the x-ray mechanism from Halite / Centurion was?

Yes.

A nice explanation is found here - https://en.wikipedia.org/wiki/LASNEX

Given the past failures and rising costs, the Department of Energy decided to directly test the concept with a series of underground nuclear tests known as "Halite" and "Centurion", depending on which lab was handling the experiment. Halite/Centurion placed typical ICF targets in hohlraums, metal cylinders intended to smooth out the driver's energy so it shines on the fuel target evenly. The hohlraum/fuel assemblies were then placed at various distances from a small atomic bomb, detonation of which released significant quantities of x-rays. These x-rays heated the hohlraums until they glowed in the x-ray spectrum (having been heated "x-ray hot" as opposed to "white hot") and it was this smooth x-ray illumination that started the fusion reactions within the fuel. These results demonstrated that the amount of energy needed to cause ignition was approximately 100 MJ, about 25 times greater than any machine that was being considered.

The data from Halite/Centurion was used to further tune LASNEX, which then predicted that careful shaping of laser pulse would reduce the energy required by a factor of about 100 times, between 1 and 2 MJ, so a design with a total output of 4 MJ began to be on the safe side. This emerged as the National Ignition Facility concept.

From Seife, Charles (2008). Sun in a Bottle: The Strange History of Fusion and the Science of Wishful Thinking. Penguin. ISBN 9781101078990.

The goal of Halite/Centurion was to determine (quantify) the necessary energy, or energy density, to accomplish inertial confinement. NIF is the result.

 

[BWV]

OK thanks

 

[Maury Markowitz]

The Halite/Centurion tests were based on the existing methods they used to test reentry vehicles.

In outer space, the x-rays from a bomb can travel long distances and the heat load on any nearby object is high enough to cause shock heating that breaks up the heat shield. This was how the later long-range interceptors were going to work, like Spartan. To counter Soviet versions of the same concept, they began testing different heat shield designs. They did this using underground tests where they would place a primary in a cavern and then drill long tunnels to the test sites. The bomb would go off and the x-rays would hit the various test objects around it. There were huge steel doors that would slam shut after the flash so the following shock wave and other debris did not hit the test articles. Wait for it to cool down and then pull them out and see what happened.

For Halite/Centurion, all they did was replace the test articles with sample fusion fuel capsules. Metal x-ray mirrors were arranged around them to focus the light. These were placed at various distances from the bomb so that they could test the effect of different amounts of x-rays impinging on them simply through the inverse square.

The result of the tests suggested 100 MJ of laser energy would be needed. This is well beyond any laser we know how to build. But they were sure they could avoid that level of energy by carefully shaping the laser pulse to deliver energy in a timed fashion - basically you want a pulse to heat up the hohlraum to working temperature, then ionizes the pusher, followed by another that does the actual collapse. Depending on the shaping they call this high foot or low foot or various other names. Using this concept (which was always the plan really) they calculated about 2 MJ would be needed.

So they build NIF with 4 MJ to be really sure. This was intended to provide gain around 50. The record gain so far is 0.7, so it looks like the original 100 MJ requirement was not far off.