DENSITY CONTROL OF A FIELD-REVERSED CONFIGURATION

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The electron density of a field-reversed configuration(FRC) plasma must be reduced about one order of the magnitude on the present experiment to make effective a neutral beam heating in an FRC reactor. Operating density in an FRC is controlled bya Paschen's law concerning to gas breakdown letween elecrodes. So it is difficult to produce the plasma at the pressure lower than the minimum of the gas breakdown.We propose a new method to generate an FRC with the density below the minimum. It is that the initial plasma which is produced above the minimum is decreased by a loss from the coil ends. The low density plasma produced by this method is used to form the FRC.The density limit of the FRC is changed from 2X10^<21>m^<-3> to 9x10^<20>m^<-3> in our experiment. If this method is applied to a large machine which was operated till now. it is possible that the target plasma to a neutral beam heating can be prepared at a density of 4x10^<20>m^<-3>. The plasma temperature goes up from 400eV to … More 900eV by ablove density change. This strong corellation between the temperature and the density is easily explained by a beta-1 condition on the FRC plasma.As the plasma parameter range treated in our machine becomes broad, other subjects to be needed in a FRC reactor are studied. These are a formation of an FRC with a high poloidal flux, a translation and a merging of FRCs. A new rheta-coil, named a control coil, is installed between the discharge tube and the rheta-pinch-coil for these experiments. The FRC becomes fat by application of a magnetic pressure of the control coil to the both ends of the FRC and has a twice of the poloidal flux without the control coil. On the translation experiment it becomes possible that an FRC can be moved at speed of 50km/s inthe same field strength as the formation region. Two FRCs are accerelated to collide each other by the control coil and are merged into one FRC.The merging process is quickly completed for 10-15mu s, of which time is preferable to a refuering in a reactor. These experiments will be tried again in quasistatic field, of which machine is constructed now. Less