English: Swan Nuclear Device consisting of a high velocity explosive outer layer with the shape of two rotating logarithmic spirals (brown) and low velocity explosive (or air) inside (yellow). The detonation waves converge spherically under the following condition: sin α = S/F. α is the pitch angle of the spiral, S(low) and F(ast) are the detonation velocities. The S/F-ratio in this animation is 1/2, hence k = tan(arcsin(1/2)) = 1/3^1/2.

Special thanks to Darel Rex Finley, who was convinced that the outer layer of the Swan Device must be two rotating logarithmic spirals: https://alienryderflex.com/swan_device_1956_probable_shape.shtml So I did the math and it turned out to be correct.

programs used:
- GeoGebra Classic
- MS Paint
- https://ezgif.com

Explosion sequence taken from https://commons.wikimedia.org/wiki/File:Implosion_bomb_animated.gif