Exploration of RF-Controlled High Current Density Hollow Cathode Concepts

Abstract

Exploration of a novel RF-Controlled HollowCathode concept is presented using finite element analysis. Commercial software is used to model the extent of RF power absorption in one configuration of such a cathode in order to describe whether the RF power is localized as in a "stinger" concept or is projected downstream to lower the emission current density while maintaining a constant discharge current. Plasma conductivity along the major axis is calculated from a baseline high current density lanthanum hexaboride hollow cathode and is used in the modeling of RF power absorption by the internal plasma. It was found that within a maximum axial distance from the orifice, a direct coaxial-cathode mating can lead to high percentages (>96%) of localized microwave power absorption. The configuration analyzed acted more as a stinger, as approximately 62% of the RF power was absorbed within 2 mm of the inner coaxial conductor tip. Xenon gas breakdown using RF waves was explored and deemed practical for the cathode parameters studied. RF heating of the emitter prior to plasma ignition was also examined, but low RF power absorption (<5%) without a lossy plasma suggested poor feasibility of this potential function.

Modeling and Development of the RF-Controlled Hollow Cathode Concept

“…The emitter region, where the thermionic emission plasma is generated, is shown as purple LaB 6 in Figure 4 and as an example two-dimensional plot of the simulated plasma density in Figure 5. As mentioned in our previous paper, 13 with the addition of a microwave source comes the addition of a source cathode which could become a life limitation. However, currently available space-qualified microwave sources (e.g.…”

Towards Next-Generation Small-Size Boron Ion Implanting Apparatus

“…In 2012, the coupling of a RF ICP or RF CCP actuator with a HC was reported by Christensen (2012) and Plasek et al (2012). It is well known that hollow cathode technologies are in high demand in analytical spectroscopy in the form of atomic resonance spectra sources for the majority of elements in Mendeleyev's periodic table.…”

Numerical simulation and experimental research on an inductively coupled RF plasma cathode

“…Therefore, an empirical value g = 0.25 i was set. R i s, detailed in [38] is the rate of surface reaction on the wall in the first term on the right side of equation (18), and the second term is the ionic migration on account of the electric field acting toward the wall, which is satisfied if the expression ( • ) > Z E n 0.…”

“…Godyak et al [3] found that in the RF plasma discharge experiments, the maximum emission efficiency of the ICP was higher than that of microwave and helicon. Other studies concerning the RF ignition of hollow cathodes can also be found in their papers [18][19][20]. Jahanbakhsh et al discussed the relationship between the electron extraction capacity and the gas flow rate, the size of the extraction aperture, and the absorbed RF power [10,21].…”