Stability Of Field-reversed Configurations Research Articles

Formation, spin-up, and stability of field-reversed configurations.

Formation, spontaneous spin-up, and stability of θ-pinch formed field-reversed configurations are studied self-consistently in three dimensions with a multiscale hybrid model that treats all plasma ions as full-orbit collisional macroparticles and the electrons as a massless quasineutral fluid. The end-to-end hybrid simulations reveal poloidal profiles of implosion-driven fast toroidal plasma rotation and demonstrate three well-known discharge regimes as a function of experimental parameters: the decaying stable configuration, the tilt unstable configuration, and the nonlinear evolution of a fast growing tearing mode.

Advances in singly connected closed field line plasma devices and extrapolation to POP level experiments and reactors

Recent advances in creating stable, hot, steady-state field-reversed-configuration (FRC) plasmas using rotating magnetic fields (RMFs) have made this an appropriate time for re-examining the old field-reversed-mirror concept. The reactor advantages of such a linear, naturally high beta configuration would be enormous, but previous attempts to produce field reversal using tangential neutral beam injection (TNBI) alone were unsuccessful. Simple scalable extensions of present RMF produced FRCs can result in ideal traps for TNBI produced energetic ions, and detailed calculations show high efficiencies of TNBI production of energetic ion rings within such FRCs. If non-standard MHD effects such as strong flow and highly energetic ions are able to extend FRC stability to larger sizes, then the principal need will be to reduce present high values of anomalous cross-field resistivity. Experimental trends show how this may be achieved, and the present experimental and theoretical status of the most basic issues of FRC stability, confinement, and current drive are summarized, along with the new calculations on TNBI. The parameters for a modest sized ‘proof-of-principle’ (POP) device which can address these basic issues, as well as provide enough flux for efficient TNBI trapping, are given.

Physics Basis and Progress for a Translating FRC for MTF

We describe a physics scaling model used to design the high density field reversed configuration (FRC) at LANL that will translate into a mirror bounded compression region, and undergo Magnetized Target Fusion compression to a high energy density plasma. At Kirtland AFRL the FRC will be compressed inside a flux conserving cylindrical shell. The theta pinch formed FRC will be expelled from inside a conical theta coil. Even though the ideal FRC has zero helicity and toroidal magnetic field, significant non-ideal properties follow from formation within a conical (not cylindrical) theta coil. The FRC stability and lifetime properties may improve. Several experimental features will also allow unique scientific investigations of this high Lundquist number but collisional plasma.

Recent Advances in the SPIRIT (Self-organized Plasma with Induction, Reconnection, and Injection Techniques) Concept

Since its inception at the 1997 Innovative Confinement Concept meeting, the Self-organized Plasma with Induction, Reconnection, and Injection Techniques (SPIRIT) concept has been continuously advanced both theoretically and experimentally. The main features of this concept are: (1) formation of large-flux Field Reversed Configuration (FRC) plasmas by merging two spheromaks with opposite helicities; (2) flexibility to assess FRC stability by varying the plasma shape and kinetic parameter, by using passive stabilizers, and by injecting energetic ions; (3) sustainment of the FRC for a time significantly longer than the energy confinement time using an ohmic transformer and/or neutral beam injection. Experiments carried out in TS-3/4 and SSX and more recently in Magnetic Reconnection Experiment (MRX) have further verified the effectiveness of this formation scheme for large-flux FRCs. An improved understanding of FRC stability over plasma shape and kinetic parameter has been obtained in MRX. New numerical simulations showed that FRC plasmas can be globally stabilized by injecting energetic ions. Many of these aspects of the SPIRIT concept can be further studied in the current MRX device.

Ideal stability of a toroidal confinement system without a toroidal magnetic field*

New results show that a toroidal plasma can be ideally stable to gross modes without a toroidal magnetic field. Previous ideal-magnetohydrodynamic (MHD) studies for such systems [commonly called field-reversed configurations (FRC)] have consistently predicted instability to the tilting mode (lowest-order kink mode). However, a new range of equilibria not previously considered are found, which are stable to tilting in ideal-MHD theory. The equilibrium properties that promote stability are hollow current profile, and racetrack separatrix shape. Stable equilibria may not be possible in a θ-pinch system, but could be achieved with a properly designed vertical field coil set. The stability of FRC’s in past θ-pinch experiments arises partly from nonideal effects, but benefits considerably from hollow current profile and racetrack separatrix shape.

Field-reversed configuration research at Los Alamos

Exploratory field-reversed-configuration (FRC) experiments, initiated at Los Alamos in the midseventies, demonstrated FRC lifetimes substantially longer than predicted from MHD stability theory. Subsequent experimental and theoretical advances have provided considerable understanding of FRC stability physics, the characteristics of the configuration loss processes, and the particle confinement scaling with size. The critical FRC physics issues, which directly relate to the development of an FRC fusion reactor and need to be addressed in a new generation of experiments, have been clearly identified.

Magnetohydrodynamic equilibrium and stability of field-reversed configurations

Magnetohydrodynamic equilibrium and stability studies of field-reversed configurations are presented. Experimentally realistic equilibria are calculated numerically for a plasma inside a conducting cylinder. Stability studies indicate that equilibria ranging from elliptical to highly racetrack-shaped are all unstable to the internal tilting mode.