THE EFFECT OF THE COLLECTOR SHEATH ON THE POTENTIAL RELAXATION INSTABILITY

The potential relaxation instability (PRI) can be excited in the magne tized plasma column of a single-ended Q-machine by drawing an electron current to a collector. This Mn either be the terminating tungsten pl ate (the cold plate (CP) or a grid (G) inserted in between. The freque ncy of the PRI, which according to the standard model should be solely determined by the length of the system, in fact also depends on the c ollector bias, the plasma density and the magnetic field. If, however, the reduction of the system length due to the electron-rich sheath in front of the collector is taken into account, in a certain range the PRI frequency becomes more independent of the external parameters.