
Overall this looks like someone asked a physics undergraduate to spend an hour imagining roughly how the well-known schematic might be fitted inside a real warhead case. It probably is exactly that. I can't imagine that showing it to the North Koreans advanced their nuclear programme by any more than fifteen minutes.
As you only require one reference, I will present K.S. Krane, Introductory Nuclear Physics, section 14.5 "Thermonuclear Weapons." The relevant schematic is numbered 14.19. I chose this because it's a textbook that I remember using myself; I'm not sure what is usually used these days.
I did the required undergraduate nuclear physics course which at the time was focused on nuclear energy. At the time a very surface level course due to being reduced in size over the years in favor or atomic and quantum physics instead.
I still have Introductory Nuclear Physics [2] sitting in my bookshelf because I never had the chance to sell it, the course was changed to be centered around particle accelerators instead.
That program used to be the prime source of people going into nuclear energy research and development. Today you can't even take it as an master, it died out due to everyone seeing it as a dead end career wise with the advent of renewables.
[1]: https://en.wikipedia.org/wiki/Nuclear_power_in_Sweden
[2]: https://www.amazon.com/Introductory-Nuclear-Physics-Kenneth-...