Quasi-isodynamic stellaratorA quasi-isodynamic (QI) stellarator is a type of stellarator (a magnetic confinement fusion reactor) that satisfies the property of omnigeneity, avoids the potentially hazardous toroidal bootstrap current, and has minimal neoclassical transport in the collisionless regime.[1] Wendelstein 7-X, the largest stellarator in the world, was designed to be roughly quasi-isodynamic (QI). In contrast to quasi-symmetric fields,[2] exactly QI fields on flux surfaces cannot be expressed analytically.[3] However, it has been shown that nearly-exact QI can be extremely well approximated through mathematical optimization,[4] and that the resulting fields enjoy the aforementioned properties. In a QI field, level curves of the magnetic field strength on a flux surface close poloidally (the short way around the torus), and not toroidally (the long way around), causing the stellarator to resemble a series of linked magnetic mirrors. References
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