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[ALT] Stellarator Fusion (Abandoned & Revived)

The stellarator is a magnetic confinement fusion device that uses a complex twisted external magnetic field to confine plasma, as opposed to the tokamak which relies on an internally generated plasma current. Invented by Lyman Spitzer (Princeton) in 1951, it was the first serious fusion machine — but was abandoned in the 1960s when the tokamak appeared simpler and more promising. It is now staging a major revival.

The Fork

What won: The tokamak — invented at the Kurchatov Institute (Artsimovich, 1958), a toroidal device in which the magnetic field for plasma confinement is partly generated by an internal plasma current driven by a transformer. Simpler to build in the 1960s; Soviet tokamak results in 1968 (T-3, Tc~10 million K) were dramatically better than contemporary stellarators, causing the US to abandon the stellarator programme.

What was abandoned: The stellarator — Spitzer's Model C at Princeton was converted to a tokamak (PLT) in 1970. The key disadvantage in the 1960s: the complex twisted coil geometry required precision engineering that was then impossible to manufacture.

Why the Stellarator May Actually Be Superior

  • Steady-state operation: Tokamaks are inherently pulsed (the plasma current must be periodically rebuilt); stellarators operate continuously without any plasma current.
  • No disruptions: Tokamak plasma can disrupt catastrophically (current collapses instantaneously), causing mechanical damage. Stellarators have no disruptions — they are inherently stable.
  • No current drive: No need for complex auxiliary current-drive systems.
  • Higher plasma density potential: Can confine denser plasmas.

The Revival: Wendelstein 7-X

Germany's Wendelstein 7-X (W7-X, Max Planck Institute, operational 2015) is the world's largest and most advanced stellarator. Its 50 non-planar superconducting coils were designed by supercomputers and manufactured to tolerances of 0.1 mm — the same precision CAD/CAM machining that was impossible in 1970. W7-X demonstrated plasma temperatures of 40 million K (2016), and energy confinement time matching predictions. In 2022, it achieved 1.3 GJ of plasma energy — a world record for stellarators. It does not produce net energy but demonstrates the physics.

Current Status

Actively revived — Helically Symmetric Experiment (HSX, Wisconsin), Quasi-Poloidal Stellarator (QPS), and private ventures (Type One Energy, Commonwealth Fusion exploring hybrid designs). If W7-X continues to validate stellarator confinement, the steady-state and disruption-free advantages could make it the preferred design for commercial fusion plants.

Discovery Character

Surprise level: High — the stellarator's abandonment in the 1970s seemed final; its revival as a computationally optimised, precision-manufactured device was not predicted.

Mode: Abandoned by empirical comparison (T-3 tokamak vs. Model C stellarator, 1968); revived by computational design — the fork was closed by Moore's Law enabling the precision manufacturing the original design required.