Business Insider and CNN  report North Korea may have tested H-bomb components. The direct translation is that they tested a Teller-Ulam design, or, at least, parts thereof. It is worth noting that the first U.S. test of the Teller-Ulam design was not a bomb. A bomb can be dropped from an airplane. The device of first U.S. thermonuclear test, Ivy Mike, weighed 82 tons, including a full-scale cryogenics plant. So a test can validate two things:

• the physical principles, or rough design
• the design of an actual weapon

In the case of North Korea, it may have been a blend. The deuterium fuel was probably in solid form. But the arrangement of the parts may have been more to validate  design principles than something that can fit on top of a rocket.

The first public disclosure of atomic weapons design  was publication by U.S. government  of the Smyth Report.  It established the  template for future  comprehensive disclosure of qualitative information about nuclear weapons design, the kind that can be conveyed in diagrams drawn on napkins, but omitting all the laborious complexity of making something that works. Quoting Wikipedia,

“For this reason, the Smyth Report focused heavily on information, such as basic nuclear physics, which was either already widely known in the scientific community or easily deducible by a competent scientist, and omitted details about chemistry, metallurgy, and ordnance. This would ultimately give a false impression that the Manhattan Project was all about physics.”

The media coverage of North Korea’s nuclear program, with multinational assessments, is more revealing than that of past proliferations. But although there is plenty of qualitative info about the Teller-Ulam design in the public domain, the level is still too detailed, more appropriate to someone trying to build an H-bomb in Mosul. Given all the interest in North Korea, the lay reader might  be interested in a few words about the design to make it real. None of what follows is based on classified information. It is derivative  of public domain info, but even more simplified.

A brief review of nuclear fusion, which  is not the Teller-Ulam design. If a container of some heavy hydrogen, a.k.a. deuterium, is compressed and heated enough, the atoms will fuse, forming helium. While “slow fusion” is routinely done in laboratories, bomb fusion is fast. No means of compressing deuterium enough exists short of the H-bomb’s ancestor, the atomic bomb.

Every H-bomb contains an A-bomb that is by itself a powerful weapon.  The first approach to the H-bomb was to surround the A-bomb with a jacket of deuterium. Surely, the shock wave of the expanding A-bomb it would compress the jacket, from the inside out, enough to get things cooking.

This turned out to be false.  It’s hard to compress something from the inside out. If you want to compress a spring, you do it from the outside in! So we should surround the H-bomb with the A-bomb, but this, too, is impossible. For a time, the H-bomb was though to be impossible to build. So Teller and Ulam defined the problem. The A-bomb has all the energy required to do the job, but there is no direct way to make it squeeze orange juice.

Teller seems to have been credited with noticing that most of the energy of an A-bomb, 80%, comes out as light. The explosive part, the other 20%, is no help. It simply destroys the gadget before it blows. But the sun’s light, and a magnifier, can be used to start a fire. Light can be put where it’s needed, to cook parts of the bomb as needed. The great intuitive leap:

Throw away the explosive part of the A-bomb effect. Use only the light of the A-bomb to cook the H-package.

Now to an amusing detail. In the Teller-Ulam design, the A-bomb is located a foot or two away from the H-package, with a metal shield between the two to protect the H-package from the explosive force A-bomb. It’s all done with light.  But how do we get the light from the A-bomb to cook the sides of the H-package?

It’s done by surrounding the H-package with the chemical equivalent of Styrofoam, the same stuff packing peanuts are made of. When heated to millions of degrees, it becomes transparent and luminous. The Styrofoam guides the light of the A-bomb around the sides of the H-package. Quickly melting, this plastic becomes a glowing gas, cooking the H-package, compressing it inwards,until, BOOM! Many details are omitted.

Along with the U.S. government public disclosures, and possible napkin diagrams, there was verbal scuttlebutt. One of these tips was that the Teller-Ulam design could not be built from plans. You had to have “help.”  With supercomputers, and stolen computer code, this may be less necessary.

Don’t send packing peanuts to North Korea.