Characterization of plasma ion source utilizing anode spot with positively biased electrode for stable and high-current ion beam extraction

Abstract

The operating conditions of a rf plasma ion source utilizing a positively biased electrode have been investigated to develop a stably operating, high-current ion source. Ion beam characteristics such as currents and energies are measured and compared with bias currents by varying the bias voltages on the electrode immersed in the ambient rf plasma. Current-voltage curves of the bias electrode and photographs confirm that a small and dense plasma, so-called anode spot, is formed near an extraction aperture and plays a key role to enhance the performance of the plasma ion source. The ion beam currents from the anode spot are observed to be maximized at the optimum bias voltage near the knee of the characteristic current-voltage curve of the anode spot. Increased potential barrier to obstruct beam extraction is the reason for the reduction of the ion beam current in spite of the increased bias current indicating the density of the anode spot. The optimum bias voltage is measured to be lower at higher operating pressure, which is favorable for stable operation without severe sputtering damage on the electrode. The ion beam current can be further enhanced by increasing the power for the ambient plasma without increasing the bias voltage. In the same manner, noble gases with higher atomic number as a feedstock gas are preferable for extracting higher beam current more stably. Therefore, performance of the plasma ion source with a positively biased electrode can be enhanced by controlling the operating conditions of the anode spot in various manners.

Measurements of fireball onset

“…6. Fireballs are just one of the several forms of sheath structure that are possible near positively biased electrodes 2 and are of interest due to their application in dust confinement, 7 plasma contactors, 8 as an ion source 9 including those which can be used in the fabrication of nanodots, 10 and as a platform to study plasma self organization 11 and nonlinear processes. 12 Fireballs also bare a resemblance to similar phenomena that occur near hollow cathode plasma sources 13,14 and may contribute to the understanding of their operation.…”

Self-consistent modeling of self-organized patterns of spots on anodes of DC glow discharges

“…The patterns are interesting also from the point of view of their technological applications. As examples, we note that single spots have been utilized as ion sources with a stable and high-current ion beam extraction [17], and recently it has been shown that self-organized patterns on liquid anodes of atmospheric pressure glow microdischarges can reveal a nontrivial cancer-inhibiting capability [18].…”

Theory and simulation of anode spots in low pressure plasmas

“…1. Anode spots are just one of the several forms of sheath structure that are possible near positivly biased electrodes 3 and are particularly of interest due to their application in electron temperature control 6 , dust confinement 7 , plasma contactors 8 , as an ion source 9 , and as a platform to study plasma self organization 10,11 . In this paper, the anode spot onset is studied in particle-incell simulations for the first time and a theory for their onset and equilibrium properties is presented.…”