The $3.5bn NIF trains 192 pulsed laser beams on to the inner surface of a centimetre-long hollow metal cylinder known as a hohlraum. Inside is a fuel capsule, which is a roughly 2 mm-diameter hollow sphere containing a thin deuterium-tritium layer. Each pulse lasts just a few nanoseconds and the lasers can deliver about 1.8 MJ of energy. This powerful blast causes the capsule to implode rapidly, creating immense temperatures and pressures inside a central “hot spot”, where fusion reactions occur.
The first stage of the plasma at NIF is in the shape of a cylinder. This is because the plasma is confined and compressed by powerful laser beams that are directed at a cylindrical target.
The cylindrical shape allows for more efficient and uniform compression of the plasma. This is important for achieving high temperatures and densities, which are necessary for fusion reactions to occur.
The shape of the plasma is controlled by the precise alignment and timing of the laser beams. This requires advanced optics and sophisticated control systems to ensure the desired shape is achieved.
The cylindrical shape allows for better control and confinement of the plasma, resulting in higher temperatures and densities. It also allows for more efficient use of the laser energy, leading to more successful fusion reactions.
Yes, other shapes such as spheres and cones have been considered and tested. However, the cylindrical shape has proven to be the most effective for achieving fusion reactions at NIF.