The route of the implosion bomb begins from the Trinity test. And it continues in modern thermonuclear weapons.

Image 1) Castle Romea was a high-yield thermonuclear weapon detonated 27 March 1954 Pacific time. The yield of that device was 11 mt. 

Implosion bomb or fission bomb is an innovation of Dr. J. Robert Oppenheimer. When we are looking at the history of nuclear weapons many physicists like Max Planck and Albert Einstein didn't believe that the implosion bomb will explode. The story tells that when the implosion weapon detonated in New Mexico Albert Einstein said, "I'm only human". 

The implosion mechanism means. That the bites of plutonium are pushed together by using the explosive lenses. Another way to detonate a fission bomb is by pumping it with electromagnetic radiation. Also, nuclear weapons can create by using uranium. But that requires extremely large chemical factories. Modern nuclear weapons are using the solid fusion stage. Normally that stage is created by using lithium. 

The detonation of that fusion or hydrogen bomb happens by using a small fission bomb that is creating the energy as the form of fusion. In a hydrogen bomb or "Teller-Ulam" design or thermonuclear weapon, the implosion bomb will send neutrons to the uranium stick inside the lithium tank. And then that natural uranium 238 turns to plutonium 239. 

That detonation sends neutrons to lithium that transforms to deuterium and tritium. The intensive heat would launch the fusion. There is no limit to the size of a fusion bomb and the most powerful of them had the yield of 50-60 megatons (Wikipedia says that the power of Tsar bomba was 50-58 megatons (Wikipedia, Tsar Bomba). That bomb code-named  Ivan the codename for the test was"Tsar" or RDS-220 detonated near Novaja-Zemlja on 30 October, 1961But the limit of the fission bomb is about 500 kiloton.

Image 2) Diagram of a gun-type fission weapon.

Image 3) Diagram of an implosion-type fission weapon.

Images: (Wikipedia/Nuclear weapon design)

Image 4) Teller Ulam design.

(Wikipedia/Thermonuclear weapon)

The power in nuclear weapons comes from radiation that comes from nuclear fission or nuclear fusion. When implosion or fusion creates high-energy particles and pumps energy in neutrons. That thing causes the radiation impact that is known as a nuclear explosion. 

The shockwave is the electromagnetic impulse. When particles are coming out from the fissile and fusion material they form the highly intensive and powerful Doppler wave. So when the nuclear reaction reaches the edge of fusion or fissile material the movement of those particles continues in the form of wave movement. 

Diagram 1)

In diagram 1: you can see how energy travels in the nuclear system. When nuclear fission (or nuclear fusion) (arrow number 1) reaches the edge of nuclear material energy continues in the form of wave movement (arrow number 2). 

Diagram 2)

Diagram 2) shows how energy travel in the regular implosion bomb arrows marked by 2  showing the direction of the bites. That is causing an implosion where the direction of the energy is portraying arrows marked number 1. If the implosion continues to one distance. That will increase the power of nuclear fission (Diagram 3). 

The situation in diagram 3 requires that the fission starts in the middle of the fission material. So that's why there is a small neutron initiator in the fission material. The mission of that system is to cause asymmetry in the fission in the fission material. 

Diagram 3)

The implosion bomb

The name of the first implosion bomb test was "Trinity". The detonation happened in Alamogordo, New Mexico.  The codename of the bomb was "Gadget", And the Trinity test was accomplished on July 16, 1945. The yield of that bomb was about 25 kt., and it was the prototype of all other nuclear weapons. 

The implosion's speed or non-controlled nuclear fission is conducted with the surface area of touching plutonium bites. If the size of the contacting surfaces is large. The implosion starts in a larger area that is increasing the power of nuclear fission. Also, the spices in fissile material like radium play a great role in nuclear fission. 

There is also possible to use the "cannon method" for launching nuclear weapons. The problem with the cannon device is that the fission material bites can move inside it. When we look at the implosion system we see that nuclear fission begins between the layers of the fission material. And that thing makes the "waste of power". The implosion or fission reaction will travel in two directions to outside and inside the ball of the fissile material. 

Animation of the action of the implosion mechanism

(Wikipedia/ Nuclear weapon design)

So if the fission begins in the middle of the plutonium ball the front of neutrons will travel as the front in one direction. That thing can be created by stressing the small bite of highly radioactive material like einsteinium. In the middle of the fission material by using laser rays. That thing allows making the implosion bomb where the neutrons and energy are traveling in one direction. 

When we are thinking about the most powerful fission device in the world, "Ivy King". This device yield was 540 Kt. That is the limit of fission devices. The reason for that was that. There were four fission units in the bomb. The radiation or energy impact of the bomb began in four points. And that caused the situation the wave movement disturbed itself. The neutron radiation pushes neutrons away from their trajectory. That effect causes the situation where the speed of fission is slowing. 

https://rarehistoricalphotos.com/gadget-first-atomic-bomb/

https://en.wikipedia.org/wiki/Einsteinium

https://en.wikipedia.org/wiki/Ivy_King

https://en.wikipedia.org/wiki/Nuclear_weapon_design

https://en.wikipedia.org/wiki/Thermonuclear_weapon

https://en.wikipedia.org/wiki/Trinity_(nuclear_test)

https://en.wikipedia.org/wiki/Tsar_Bomba

Image 1)http://www.nuclearweaponarchive.org/Usa/Tests/Castle.html

Other mages: https://en.wikipedia.org/wiki/Nuclear_weapon_design