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Shiva laser
The Shiva laser was a powerful 20-beam infrared neodymium glass (silica glass) laser built at Lawrence Livermore National Laboratory in 1977 for the study of inertial confinement fusion (ICF) and long-scale-length laser-plasma interactions. The device was named after the multi-armed form of the Hindu god Shiva, due to the laser's multi-beamed structure. Shiva was instrumental in demonstrating a particular problem in compressing targets with lasers, leading to a major new device being constructed to address these problems, the Nova laser.
==Background==
The basic idea of any ICF device is to rapidly heat the outer layers of a "target", normally a small plastic sphere containing a few milligrams of fusion fuel, typically a mix of deuterium and tritium. The heat burns the plastic into a plasma, which explodes off the surface. Due to Newton's Third Law, the remaining portion of the target is driven inwards, eventually collapsing into a small point of very high density. The rapid blowoff also creates a shock wave that travels towards the center of the compressed fuel. When it meets itself in the center of the fuel, the energy in the shock wave further heats and compresses the tiny volume around it. If the temperature and density of that small spot is raised high enough, fusion reactions will occur.
The fusion reactions release high-energy particles, which collide with the high density fuel around it and slow down. This heats the fuel further, 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 where the shock wave started the reaction. 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 in order to compress the core before it disassembles, as well as creating a suitable shock wave. The laser beams must also be focussed evenly across the target's outer surface in order to collapse the fuel into a symmetric core. Although other "drivers" have been suggested, lasers are currently the only devices with the right combination of features.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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