CONTROLLING THE APPEARANCE AND DYNAMICS OF A PLASMA BALL OF FIRE BY USING AN ADDITIONAL ELECTRODE

摘要

By applying a positive potential in respect with the plasma potential on a disk electrode immersed in plasma, we obtained a quasi-spherical, intense luminous body, attached to the electrode, known as ball of fire ox fireball. Experimental investigations have proved that this body is a complex space charge configuration consisting of a positive nucleus (plasma enriched in positive ions) bordered by a double layer. At high potential on the electrode, this structure performs a proper dynamics, sustained by periodic formations and disruptions of the double layer. In order to control the appearance and the dynamics of such a structure, we used an additional ring electrode surrounding the disk electrode. The obtained experimental results proved that the potential threshold of the appearance of the structure strongly depends on the negative bias of this additional electrode. With the increasing of the negative potential on the ring electrode, the stability domain of the structure can be reduced to only one point, which means that the structure becomes unstable immediately after its appearance. In the oscillatory mode, the frequency of the oscillations is also strongly influenced by the potential of the ring electrode. This happens because the oscillation frequency depends on the dc component of the current collected by the disk electrode, and this current depends on the potential of the ring electrode. The results can stay at the basis of an efficient method to control the appearance and the dynamics of complex phenomena in plasma. This method can be successfully used to control or even eliminate, if necessary, plasma instabilities.