Confinement of a dense plasma by a static magnetic and stationary electromagnetic fields

Abstract

The confinement of a plasma by the radiation pressure of a stationary electromagnetic wave has been proposed and made the subject of experiments by different authors. In these various projects and devices, the HF field creates and confines the plasma. In the device described here one starts with a cavity containing a plasma that is pre-formed and pre-heated in order to fix the mode, to facilitate the tuning of the oscillators exciting the cavity and to permit investigation of the reduction in frequency resulting from the evolution of the plasma. The initial plasma in the form of a spindle is strongly ionized (>> 50%) and of high density (> 1013 e/cm3). The spherical cavity, in the absence of plasma, is resonant at ∼1130 MHz in the mode H101. The depth of penetration (< 2 mm) is a small fraction of the diameter of the plasma (∼6 cm). The plasma behaves like a metallic conductor. Use of two H101 modes perpendicular to one another in space gives a confinement with no gap. The initial plasma is created by means of a pulsed reflex discharge (pulse length ∼100 μsec) of which the cavity constitutes the interanode section. Controllable densities from 1012 to 1014 e/cm3 are readily obtained. The portion of the discharge situated outside the cavity allows the determination of the parameters of the discharge. A system of eight pulsed auto-oscillators (total power 200 kW, pulse length ∼100 μsec) are coupled to the cavity and regulated in such a manner that oscillation frequency will be near the theoretical resonance frequency of the cavity containing the plasma. In this way the radiation pressure is maintained in spite of the variations in diameter and form of the plasma. The power delivered increases progressively as the resistivity of the plasma diminishes. The couplings of the oscillators to the cavity are capable of being oriented in an arbitrary manner. One can thus either fix the axis of the mode or choose an operational regime with one or two modes. Windows are provided for the application of various diagnostic techniques: ultra-fast cinematography and image convertor for the study of the evolution of the plasma optical interferometry with time resolution (Perrot-Fabry) for the measurement of ion temperature UHF interferometry at 8 and 4 mm for the determination of the electron density Langmuir probes placed in the wall thickness and along the axis of a mode for the measurement of radial leakage flux.