Nuclear weapon design

North Korea declared itself a thermonuclear power on Sept. 3, after carrying out a sixth nuclear test more powerful than any it has previously detonated, presenting President Donald Trump with a potent challenge.
 
The North has tested a hydrogen bomb with "perfect success", a jubilant newsreader announced on state television, adding the device could be mounted on a missile.

The recent flight tests of an upgraded nuclear bomb in the Nevada desert mean that the United States is preparing for war, military analyst Oleg Glazunov told Sputnik.

Despite posing no direct threat to Russia, the recent test of the bomb "means that the Americans are preparing for war", Glazunov said.

Because of their top secret status, about 10,000 reels of film recording the 210 above-ground nuclear tests conducted by the United States between 1945 and 1962 were allowed to rot in high-security vaults across the country.

North Korea said it successfully tested a miniaturised hydrogen nuclear device on Jan. 6, claiming a significant advance in the isolated state's strike capability and setting off alarm bells in Japan and South Korea.

The test, the fourth time North Korea has exploded a nuclear device, was ordered by young leader Kim Jong Un, state media said.