National Ignition Facility reaction chamber. (Source: Wikipedia.org)

A spherical vacuum chamber in the centre of which the inertial fusion is ignited. The chamber has apertures in its walls for the passage of laser beams. A target in the centre of the chamber is compressed by the lasers. After successful compression, the thermonuclear fusion is initiated in the centre of the peppercorn-sized target. The chamber must be sufficiently large, about 10 metres in diameter, to avoid damage from the energy generated and from the flying remnants of the target. The reaction chamber is made of concrete covered on the inside with a few centimetres of aluminium, with penetrations for lasers, diagnostics, a target-holding arm, and vacuum pumps, which must maintain a vacuum throughout the interior of the reaction chamber.