Principal physics of rotating magnetic-field current drive of field reversed configurations

• Published in: Physics of plasmas 2006-01, Vol.13 (1)
• Main Authors: Hoffman, A. L., Guo, H. Y., Miller, K. E., Milroy, R. D.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CHARGED-PARTICLE TRANSPORT; ELECTRIC CURRENTS; ELECTRON TEMPERATURE; ELECTRONS; FIELD-REVERSED THETA PINCH DEVICES; ION TEMPERATURE; IONS; MAGNETIC FIELDS; MAGNETOHYDRODYNAMICS; PLASMA; PLASMA CONFINEMENT; PLASMA DENSITY; PLASMA PRESSURE; REVERSE-FIELD PINCH; REVERSED-FIELD PINCH DEVICES; ROTATION
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/1.2162052

After extensive experimentation on the Translation, Confinement, and Sustainment rotating magnetic-field (RMF)-driven field reversed configuration (FRC) device [A. L. Hoffman et al. , Fusion Sci. Technol. 41, 92 (2002)], the principal physics of RMF formation and sustainment of standard prolate FRCs inside a flux conserver is reasonably well understood. If the RMF magnitude B ω at a given frequency ω is high enough compared to other experimental parameters, it will drive the outer electrons of a plasma column into near synchronous rotation, allowing the RMF to penetrate into the plasma. If the resultant azimuthal current is strong enough to reverse an initial axial bias field B o a FRC will be formed. A balance between the RMF applied torque and electron-ion friction will determine the peak plasma density n m ∝ B ω ∕ η 1 ∕ 2 ω 1 ∕ 2 r s , where r s is the FRC separatrix radius and η is an effective weighted plasma resistivity. The plasma total temperature T t is free to be any value allowed by power balance as long as the ratio of FRC diamagnetic current, I ′ dia ≈ 2 B e ∕ μ o , is less than the maximum possible synchronous current, I ′ sync = ⟨ n e ⟩ e ω r s 2 ∕ 2 . The RMF will self-consistently penetrate a distance δ * governed by the ratio ζ = I ′ dia ∕ I ′ sync . Since the FRC is a diamagnetic entity, its peak pressure p m = n m k T t determines its external magnetic field B e ≈ ( 2 μ o p m ) 1 ∕ 2 . Higher FRC currents, magnetic fields, and poloidal fluxes can thus be obtained, with the same RMF parameters, simply by raising the plasma temperature. Higher temperatures have also been noted to reduce the effective plasma resistivity, so that these higher currents can be supported with surprisingly little increase in absorbed RMF power.