Inertial confinement fusion
Inertial fusion relies on the particles' inertia to make fusion possible. Since the energies required to achieve fusion are huge (velocities of about 1000km/s are in order), fusion has to take place in the very short time interval between the moment the particles are heated and the moment they fly apart on account of their obtained, large velocity.
Gigantic, powerful lasers are used as the heating source. Shining laser energy on fuel pellets triggers an inward shock wave that allows the temperature and pressure needed for fusion to be reached in the core of the pellet.