system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why haven't we developed energy applications based on fusion, yet we can make weapons that use fusion quite effectively (i.e. hydrogen bombs)?
gpt
Thermonuclear (fusion) weapons create a very fast and violent reaction that puts out a huge amount of energy very quickly, but are over the second after they begin. The fusion portion of the weapon actually needs a fission bomb to get it started.

Fusion reactors on the other hand, need a slow stable reaction that keeps going. Research is constantly being done, but there are some challenges:

1) Starting the reaction - detonating an atomic warhead in your reactor is a poor way to kickstart your reactor. Better methods are in the works.

2) Maintaining the reaction - as the fusion reaction goes on, the fuel wants to separate, ending the reaction. A method is needed to keep the hydrogen isotopes packed together.

3) Containing and using the reaction - most materials do not hold up well to the extreme heat generated by the reaction. A method to contain the reaction while drawing heat from it is necessary, without having to constantly turn the reactor off for maintenance.