Radial Compression of a Compact Toroid Caused by Induction of a Paramagnetic Field

Abstract

Partially ionized and weakly magnetized plasma (typical for MHD generators) flows along the outer spherical chamber, and is placed around the inner chamber where an field reversed configuration (FRC) is injected. Inside the outer chamber, the azimuthal E_r × B drift induces a paramagnetic field B_p, with an intensity of tens of Teslas. The intensity of the B_p field is controlled by the inwardly directed radial electric field E_r. Inside the inner chamber the B_p field becomes anti-parallel to the external magnetic field B_em. After establishing the magnetic mirror configuration of magnetic field intensity B_p ~ 20T (in the mid-plane), the FRC (target plasma) is injected into the magnetic mirror with the help of a magnetic wave generator. Inside the magnetic mirror (inner chamber), the rotating magnetic field (RMF) induces the azimuthal current j_ω inside the FRC. This current gives the magnetic field B_j an intensity of dozens of Teslas. This field is antiparallel to the B_p field. Interaction between magnetic fields, B_p and B_j, causes radial compression of the injected FRC. As a result of the magnetic compression, the product of density and the energy confinement time amounts to 1.72 × 10¹⁹ s/m³, which is close to the level expected for the working reactor (~10²⁰ s/m³). Detailed analyses reveal that the compressed plasma (compact toroid) is very stable, the kinetic stability condition is fulfilled (S*/ε≅0.28), and the ratio α is very low: (~8.6×10^-2). This makes the most destructive rotational modes, n=1 and n=2, harmless.