Houyang Guo

Formation and steady-state maintenance of field reversed configuration using rotating magnetic field current drive

Rotating magnetic fields (RMF) have been used to both form and maintain field reversed configurations (FRC) in quasisteady state. These experiments differ from steady-state rotamaks in that the FRCs are similar to those formed in theta-pinch devices, that is elongated and confined inside a flux conserver. The RMF creates an FRC by driving an azimuthal current which reverses an initial positive bias field. The FRC then expands radially, compressing the initial axial bias flux and raising the plasma density, until a balance is reached between the RMF drive force and the electron–ion friction. This generally results in a very high ratio of separatrix to flux conserver radius. The achievable final conditions are compared with simple analytic models to estimate the effective plasma resistivity. The RMF torque on the electrons is quickly transferred to the ions, but ion spin-up is limited in these low density experiments, presumably by ion-neutral friction, and does not influence the basic current drive process...

Sustainment of elongated field reversed configurations with localized rotating magnetic field current drive

The effects of rotating magnetic field (RMF) antenna length on the sustainment of RMF driven field reversed configurations (FRC) have been investigated in the Translation, Confinement, and Sustainment (TCS) facility. FRCs could be sustained with axial lengths well beyond the RMF antenna, presumably due to induced axial flow. The FRC length, ls, in TCS was weakly dependent on the antenna length, la, with ls∼2la being achieved for the shortest antenna employed. Reducing antenna length led to more stable operation, with the FRCs less prone to rotational instabilities. Shorter antenna lengths also resulted in increases in the plasma temperature. At larger ratios of ls/la the RMF had to supply a greater torque per unit length, and it did this by increasing its penetration into the FRC, brought about automatically by a slight decrease in plasma density. Optimal overall current drive efficiency occurred at values of la/2rs of about 1.3, where rs is the separatrix radius, and values of ls/la of about 1.5. In cont...