Fluctuation in a helicon plasma with additional immersed antenna

Fluctuations in the floating potential are measured in a cylindrical magnetised plasma, as the phase between a "primary" Helicon antenna and a "secondary" immersed antenna is varied. The two antennas are powered by separate radio frequency (RF) generators of 13.56 MHz controlled by a single oscillator and phase shifter. The Helicon antenna is separated from the plasma by a glass tube, while the immersed copper antenna is in direct contact with the plasma. The image presented here shows floating potential fluctuations of ∼100 Hz where the amplitude of the fluctuations vary dramatically with the phase between the two RF generators.