Theoretical study on production of super high beta plasmas by rotating magnetic field

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The stability of the rotation of the ion and electron fluids is studied on the balance of the forces exerted on the electrons by the resistive friction and the Rotating Magnetic Field (RMF) applied for the sake of maintaining Field Reversed Configuration (FRC) in steady state. The simple analytical model such as infinite-long plasma, rigidly rotating ions and electrons and uniform plasma density are used. The linear stability analysis of the equilibrium rotation is carried out in the reduced zero-dimensional model which includes the effects of ion rotation, radial plasma flow and separatrix radius change due to the flux conservation within the flux conserver. The analytical expression which gives the stability criterion is derived from the eigenvalues of the linearized equations. Based upon the stability criterion, an interpretation of the present experimental results and comments of the future experiments are given as for the penetration of the RMF into the FRC.The transient behaviors … More of current drive with an RMF in an FRC are studied by numerically solving the rate equations for the ion and electron rotations with the non-equilibrium initial values. The dynamic responses are investigated by introducing the perturbation into the equilibrium ion and electron rotations in order to examine the stability around the equilibrium of the shallow penetration of an RMF. The electron rotation on the stable equilibrium of the shallow penetration remains to be near the initial equilibrium so long as the perturbation is small. On the other hand, the electron rotation in the unstable equilibrium increases to be synchronous with an RMF and to result in the full penetration for the positive perturbation and decreases further behind an RMF for the negative one. The results are consistent with the linear stability analysis.The criterion for the penetration of an RMF in an FRC is derived theoretically on a physical base that the driving force of an RMF acting directly on an electron fluid must exceed the ion drag force throughout the process for the electron fluid to reach the synchronous rotation with the RMF, resulting in the full penetration of RMF in an FRC. The criterion explains the numerical simulation results and the experimental observations better than those previously used. The criterion is also useful for the guide of the experiments of making a hot FRC in a steady state by applying a rotating magnetic field. Less