A method of producing a localized concentration of energy includes providing a series of projectiles and firing the projectiles at a target. An apparatus for producing localized concentration of energy includes: a mechanism to provide a series of projectiles and a mechanism to fire the projectiles at a target. The target is configured such that upon striking the target, a projectile traps and compresses a volume of gas between the projectile and the target. The target and the projectile are also configured such that impact of the projectile onto the target gives rise to a converging shockwave inside the trapped volume of gas.