Dielectric resonator antenna for high power RF plasma applications

Abstract

Some of the numerous applications of the inductively coupled plasma, at both atmospheric and low pressure, include plasma manufacturing, optical and mass spectroscopy, gasification and plasma reforming, semiconductor fabrication, in-space propulsion, gas lasers, ion sources, and fusion. A coil of copper or silver-plated tubing is typically used to couple the radio-frequency power into the plasma. Although this technology has been used extensively for many decades, an RF coil suffers from limitations which negatively affect the quality of the generated plasma and increase the complexity of the plasma source. These limitations include high ohmic losses in the antenna conductor which necessitate fluid cooling, high levels of capacitive coupling which necessitate RF shielding, high inter-turn voltage which limits the maximum power due to electric breakdown, external tuning capacitors which add to the size and cost, material properties of copper which demand a vacuum or thermal barrier between the coil and the plasma, etc.We will present a remarkable alternative to an RF coil which addresses all of the limitations mentioned above. It increases the maximum power limit by an order of magnitude while operating at a very high efficiency and producing high quality uniform plasma, without the need for RF shielding, and is fully compatible with high vacuum, high purity, and high temperature environment. This is possible due to the outstanding electrical, thermal, and mechanical properties of the advanced technical ceramics. We have used such ceramic materials to construct ring shaped dielectric resonators whose dielectric polarization currents replace the conduction currents of a copper coil.Polarization currents offer many advantages over conduction currents in plasma applications. One of the most outstanding properties of a dielectric resonator is that it completely eliminates capacitive coupling as the resonator maintains exactly zero RF potential even under full power. We will describe the construction and optical plasma diagnostics of prototype plasma sources for both atmospheric pressure thermal plasma at 2.45GHz in air and Nitrogen 1 and low pressure cold plasma at 430MHz in Argon at power levels up to 1kW. In addition, we will show conceptual solutions for the implementation of dielectric resonator antennas in many of the inductively coupled plasma applications.1.

Characterizing a nitrogen microwave inductively coupled atmospheric-pressure plasma ion source for element mass spectrometry

“…2. The rst group ( 7 Li, 23 Na, 24 Mg, 39 K, 85 Rb, 88 Sr, 115 In, 133 Cs, 137 Ba, and 175 Lu) is governed by elements with a low rst IE, whose sensitivity increases with higher gas ow rates due to the higher sampling efficiency. Since many analytes in this group have a low mass, a higher operating power decreases the sensitivity through increased radial diffusion and possibly space charge effects at higher temperatures.…”

“…19,20 Such microwave induced plasmas have also been described with elemental MS, [21][22][23] which however did not receive much attention. Most recently a new conguration of an inductively coupled microwave plasma source was introduced, 24 which can be operated with nitrogen as plasma gas while being capable of delivering a power of up to 1.5 kW, which compares favourably with common Ar ICPs. This novel microwave inductively coupled atmospheric pressure plasma (MICAP) has already been successfully employed as a plasma source for ICP optical emission spectrometry 25 and an initial study 26 using a prototype time-of-ight MS has revealed that with solution nebulization, the sensitivities were lower by a factor of two than those of an Ar ICP coupled to the same MS. Desolvation of the aerosol was found to enhance the sensitivity signicantly and most recently solution nebulization and laser ablation sampling were employed with an ion source coupled to a quadrupole MS (QMS), where similar gures of merit to those obtained with an Ar ICP were obtained.…”

New inductively coupled plasma for atomic spectrometry: the microwave-sustained, inductively coupled, atmospheric-pressure plasma (MICAP)

“…Theory and design of the MICAP have been described earlier, [20][21][22][23] so only qualitative descriptions of the operating principles and waveguide will be provided here. A crosssectional view of the waveguide, resonator, and torch of the MICAP is shown in Fig.…”

Merits of microwave plasmas for optical emission spectrometry – characterization of an axially viewed microwave-sustained, inductively coupled, atmospheric-pressure plasma (MICAP)

“…The most recent contribution to the eld of microwave plasmas in analytical chemistry is the microwave-sustained, inductively coupled, atmospheric-pressure plasma (MICAP) developed by Jevtic, Menon and Pikelja in 2016. 22 The MICAP uses a microwave-driven dielectric resonator formed by an aluminum oxide ring. Inside this ring, a standard ICP quartz torch is installed.…”