Edit: After further study, I have decided that the shape of the North Korea warhead does not suggest, with any strength, “Layer Cake.” The description of the U.S. W80 has been corrected.
The shape is probably the result of a extra bulk in the primary from unsophisticated explosive lenses, and a small secondary to save material.
It is still possible that elements of “Layer Cake” are included, but the idea doesn’t satisfy Occam’s Razor.
This is republished to include the possibility of Andrei Sakharov’s design.
- The 10X tremor strength reported by Japan is easily in range of a large boosted fission weapon, such as the British Orange Herald device.
- The North Koreans mastered radiation implosion on their first try. Since this is unlikely, it would indicate a major intelligence failure.
- A third path of proliferation, providing a turn-key design – Andrei Sakharov’s Soviet design, known as “Layer Cake.”
Although we don’t have access to the U.S. intelligence product that could affirm thermonuclear, there is usually a parallel in open source analysis that approximates it. But it’s not out there.
The third path would be a design easy for North Korea to replicate from plans. “Layer Cake” fits this bill. Quoting Reuters,
The shape shows a marked difference from pictures of the ball-shaped device North Korea released in March last year, and appears to indicate the appearance of a two-stage thermonuclear weapon, said Lee Choon-geun, senior research fellow at state-run Science and Technology Policy Institute.
If this was Iran, we would say it was a dummy. Possibly so. But the RDS-6 device of the Soviet Joe-4 test in 1953 was a gun-type weapon, that used deuterium outside the uranium core, not a true “thermonuclear” device, but with a yield of 400kt. It also fits the general profile of the pictures. As a very old weapon, the design might have traveled on paper via aged Soviet scientists desperate for cash after the Soviet breakup.
Compare the (CNN) North Korea photo with a photo of the U.S. model W80. In the North Korea photo, the primary (in a gun-type weapon, the “target”) is on the left, indicated by the tube supplying tritium for the primary “boost” from the tank on the green table. In the U.S. photo, the primary is on the left.
(Nuclearweaponsarchive.org.: Gun-type weapons can be boosted, which the South Africans considered, by using the barrel/projectile as a piston. )
The alternative is the proliferation of a modern Teller-Ulam design, with a completely successful test on the first try. Perhaps some ex-Soviet physicists are living in luxury in North Korea. But the shape of the package adds to my skepticism.
The North Korea (photo) warhead looks like a dumbbell connected by a narrow neck. The globe on the right side, connected by a narrow neck to the primary does not resemble the functional shape of a Teller-Ulam secondary. The great secret of the Teller-Ulam design, that the U.S. fought so hard to keep, is that the secondary of a hydrogen bomb is set off by radiation, what we call light, not touch. The radiation channel is just under the skin of the device, surrounding the secondary material. It needs the most direct way possible for the fission primary to illuminate the channel. And so,
- The kink in the housing of the North Korea package doesn’t help. But the shape is fine for Sakharov’s “Layer Cake.” The smaller, near end of the dumbbell can hold the breech of the gun.
- The U.S. warhead (photo) has no neck between the fission primary on the left
, and the fusion secondary on the right . So as much as possible, the light emitted by the fission primary has an unobstructed view of the radiation channel.
Since the North Korea pattern is to announce events that are somewhat in advance of actual progress, it is possible that the strata, the rock in which the test device was placed, was deliberately chosen to be harder than usual. This would increase the signal received by distant seismic detectors.