The High Power laser Energy Research facility (HiPER), is a proposed experimental laser-driven inertial confinement fusion (ICF) device undergoing preliminary design for possible construction in the European Union. As of 2019, the effort appears to be inactive. HiPER was designed to study the "fast ignition" approach to generating nuclear fusion, which uses much smaller lasers than conventional ICF designs, yet produces fusion power outputs of about the same magnitude. This offers a total "fusion gain" that is much higher than devices like the National Ignition Facility (NIF), and a reduction in construction costs of about ten times. This opened a window for a small machine to be rapidly built that would reach ignition before NIF. HiPER and the Japanese FIREX designs intended to explore this approach. However, research into the fast ignition approach on smaller machines like the Omega laser in the US demonstrated a number of problems with the concept. Another alternative approach, shock ignition, began to take over future development starting around 2012. HiPER and FIREX both appear to have seen no additional development since that time. HiPER should not be confused with an earlier ICF device in Japan known as "HIPER", which has not been operational for some time.
Background
Inertial confinement fusion (ICF) devices use "drivers" to rapidly heat the outer layers of a "target" to compress it. The target is a small spherical pellet containing a few milligrams of fusion fuel, typically a mix of deuterium and tritium, or "D-T". The heat of the laser burns the surface of the pellet into a plasma, which explodes off the surface. The remaining portion of the target is driven inward due to Newton's third law, collapsing into a small point of very high density. The rapid blowoff also creates a shock wave that travels toward the center of the compressed fuel. When it reaches the center of the fuel and meets the shock from the other side of the target, the energy in the center further heats and compresses the tiny volume around it. If the temperature and density of that small spot can be raised high enough, fusion reactions will occur. This approach is now known as "hot-spot ignition" to distinguish it from new approaches. The fusion reactions release high-energy particles, some of which (primarily alpha particles) collide with the high density fuel around it and slow down. This heats the surrounding fuel, and can potentially cause that fuel to undergo fusion as well. Given the right overall conditions of the compressed fuel – high enough density and temperature – this heating process can result in a chain reaction, burning outward from the center. This is a condition known as "ignition", which can lead to a significant portion of the fuel in the target undergoing fusion, and the release of significant amounts of energy. To date most ICF experiments have used lasers to heat the targets. Calculations show that the energy must be delivered quickly to compress the core before it disassembles, as well as creating a suitable shock wave. The energy must also be focused extremely evenly across the target's outer surface to collapse the fuel into a symmetric core. Although other drivers have been suggested, notably heavy ions driven in particle accelerators, lasers are currently the only devices with the right combination of features.
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