Diamagnetic “bubble” equilibria in linear traps

• Published in: Physics of plasmas 2016-08, Vol.23 (8)
• Main Author: Beklemishev, A. D.
• Format: Article
• Language: English
• Subjects: Bubbles; Confinement; Diamagnetism; Fusion reactors; Magnetic flux; Measuring instruments; Plasma; Plasma equilibrium; Plasma physics; Stability; Transport equations; Tubes
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/1.4960129

The plasma equilibrium in a linear trap at β ≈ 1 (or above the mirror-instability threshold) under the topology-conservation constraint evolves into a kind of diamagnetic “bubble.” This can take two forms: either the plasma body greatly expands in radius while containing the same magnetic flux, or, if the plasma radius is limited, the plasma distribution across flux-tubes changes, so that the same cross-section contains a greatly reduced flux. If the magnetic field of the trap is quasi-uniform around its minimum, the bubble can be made roughly cylindrical, with radius much larger than the radius of the corresponding vacuum flux-tube, and with non-paraxial ends. Then the effective mirror ratio of the diamagnetic trap becomes very large, but the cross-field transport increases. The confinement time can be found from solution of the system of equilibrium and transport equations and is shown to be τ E ≈ τ ∥ τ ⊥ . If the cross-field confinement is not too degraded by turbulence, this estimate in principle allows construction of relatively compact fusion reactors with lengths in the range of a few tens of meters. In many ways, the described diamagnetic confinement and the corresponding reactor parameters are similar to those claimed by the field-reversed configurations.