High-density Helicon Plasma Source Research Articles

High-Density Helicon Plasma Source for Linear Plasma Generators

High-Density Helicon Plasma Source for Linear Plasma Generators

Radio Frequency Excited Plasma Discharge Simulation for Potential Helicon Plasma Thruster

The development of advanced propulsion is the key element in the implementation of a robust space exploration program. Advance thruster concepts such as the development of electrodeless Plasma thrusters with high-density helicon plasma sources expected to mitigate the existing problems of the finite lifetimes inherent in electric propulsion. Electrodeless plasma thrusters are potentially more durable than conventional thrusters that use electrodes such as a gridded ion, Hall thrusters, arcjets, and resistojets. The goal of the research is to simulate a compact high-power-density helicon plasma source operating, which is under examination for a potential electric propulsion application. Plasma modeling is performed in COMSOL Multiphysics plasma module. A Nagoya type III antenna is placed on the surround of a dielectric tube and electrically excited at 13.56 MHz. Plasma is formed in the ionization chamber, which contains argon gas at low pressure. The plasma is sustained utilizing electromagnetic induction.

Development of Electrodeless Plasma Thrusters With High-Density Helicon Plasma Sources

Helicon plasma sources are very useful in many aspects and are applicable to many fields across science and technology, as they can supply high-density $({\sim}10^{13}~{\rm cm}^{-3})$ plasmas with a broad range of external operating parameters. In this paper, developed, featured sources with various sizes are characterized along with discussions on their particle production efficiency. This paper aims to develop systems that can realize schemes with completely electrodeless plasma production and acceleration. This is expected to mitigate the existing problems of the finite lifetimes inherent in electric plasma propulsion tools. Experimental and theoretical approaches that implement such schemes are presented.

High-Density Helicon Plasma Sources: Basics and Application to Electrodeless Electric Propulsion

The development of unique, high-density helicon plasma sources is described. Characterization of the largest and the smallest source sizes is made along with a discussion of particle production efficiency using Ar gas. Next, we describe an application of helicon sources to plasma propulsion using a new advanced concept without any eroding electrodes, as a review of our Helicon Electrodeless Advanced Thruster (HEAT) project.

Characteristics of low-aspect ratio, large-diameter, high-density helicon plasmas with variable axial boundary conditions

A low-aspect ratio, high-density helicon plasma source with a large-diameter of ∼74 cm that utilizes an end-launch flat-spiral antenna has been characterized under three different axial boundary conditions. Whereas one end of the device is a quartz-glass window through which an excitation rf wave is injected, the other end is a movable plasma terminating plate of three different kinds: (1) metal with small holes, (2) solid metal, and (3) solid insulator. Using this movable plate, the device aspect ratio A (device axial length/device diameter) can be reduced to ∼0.075 corresponding to the device axial length of 5.5 cm. The plasma production efficiency (PPE, defined as the ratio of the total number of electrons in the plasma to the input rf power) and helicon wave structures are examined for plasmas with various aspect ratios and boundary conditions to characterize our helicon device. Even for the lowest aspect ratio case (A ∼0.075), a plasma with the electron density of 7.5 × 1011 cm−3 can be produced. The PPE of our device is higher than that of other helicon devices that utilize winding-type antennas. Discrete axial wave modes, which can be explained by a simple model, have been identified for helicon waves excited in our low-aspect ratio helicon plasmas. A comparison between the experimental results and helicon wave theory suggests that second order radial modes must have been excited when the electron density is sufficiently high.

Large-area high-density helicon plasma sources

High-density (1012–1013 cm−3) helicon plasmas produced using two different but similar devices whose diameters are very large, 40 cm and 74 cm, respectively, have been characterized. A scaling of the particle production efficiency has been investigated in detail into a low aspect ratio (the ratio of the diameter to the axial length) region down to 0.075. It has been found that reducing this ratio manifests the standing wave-like patterns of the excited radio frequency (rf) fields. Spatial profiles of the electron density and the rf wave fields are measured, showing the effectiveness of the control of these profiles by changing the magnetic field configurations near the excitation antenna. Finally, high-beta plasmas with up to β ∼ 0.8, that exhibit diamagnetic character, where β is the ratio of the plasma pressure to the magnetic pressure, have been produced with low magnetic fields.

Development of high-density helicon plasma sources and their applications

We report on the development of unique, high-density helicon plasma sources and describe their applications. Characterization of one of the largest helicon plasma sources yet constructed is made. Scalings of the particle production efficiency are derived from various plasma production devices in open literature and our own data from long and short cylinder devices, i.e., high and low values of the aspect ratio A (the ratio of the axial length to the diameter), considering the power balance in the framework of a simple diffusion model. A high plasma production efficiency is demonstrated, and we clarify the structures of the excited waves in the low A region down to 0.075 (the large device diameter of 73.8 cm with the axial length as short as 5.5 cm). We describe the application to plasma propulsion using a new concept that employs no electrodes. A very small diameter (2.5 cm) helicon plasma with 1013 cm−3 density is produced, and the preliminary results of electromagnetic plasma acceleration are briefly described.

High-density plasma silicon oxide thin films grown at room-temperature

The fabrication at room-temperature of thin (<8nm) silicon oxide films has been achieved, in a high-density helicon plasma source reactor using Ar/O2 mixture, exhibiting relatively low concentratio...

High-density plasma silicon oxide thin films grown at room-temperature

The fabrication at room-temperature of thin (<8nm) silicon oxide films has been achieved, in a high-density helicon plasma source reactor using Ar/O2 mixture, exhibiting relatively low concentration of fixed oxide and interface charges, after annealing. The developed plasma oxidation process was employed in order to fabricate SOI-MOSFETs at low thermal budget with competitive operating characteristics.

Development of a strong field helicon plasma source

We developed a high-density helicon plasma source with a very strong field of up to 10kG. Using a double-loop antenna wound around a quartz tube, 9.5cm in inner diameter and 90cm in axial length, initial plasmas with a high density more than 1013cm−3 were successfully produced with a radio frequency power less than a few kilowatts, and with changing magnetic fields, fill pressures, and gas species.

Characteristics of a large volume, helicon plasma source

A high-density helicon plasma source with very large volume, 75cm in diameter and 486cm in axial length, has been developed, and its characteristics have been investigated. Furthermore, the radial density profile control has been successfully demonstrated by utilizing two techniques: (1) by changing the magnetic field configurations near the antenna and (2) by changing the antenna radiation-field patterns. Using two types of large-diameter spiral antennae, plasma with density exceeding 1012cm−3 has been produced with several hundreds of watts of radio frequency power. By changing the magnetic field configuration near the antenna, the threshold power and the degree of the density change in a density jump can be varied. The electron density reaches the maximum away from the antenna; then decays weakly along the axial direction.

Development of very large helicon plasma source

We have developed a very large volume, high-density helicon plasma source, 75 cm in diameter and 486 cm in axial length; full width at half maximum of the plasma density is up to ∼42 cm with good plasma uniformity along the z axis. By the use of a spiral antenna located just outside the end of the vacuum chamber through a quartz-glass window, plasma can be initiated with a very low value of radio frequency (rf) power (&amp;lt;1 W), and an electron density of more than 1012 cm−3 is successfully produced with less than several hundred Watt; achieving excellent discharge efficiency. It is possible to control the radial density profile in this device by changing the magnetic field configurations near the antenna and/or the antenna radiation-field patterns.

Etching characteristics of magnetic materials (Co, Fe, Ni) using CO/NH 3 gas plasma for hardening mask etching

Etching of magnetic materials, NiFe, CoFe, and Fe, has been studied with a high-density helicon plasma source using non-corrosive CO/NH 3 gas. High etch rates, ranging from 45 to 130 nm/min, were achieved. The etch rate strongly depended on both plasma density and ion energy. The main etching mechanism is interpreted as physical sputtering rather than as chemical reaction. A high selectivity of 6–16 was achieved by using hard masks of Ti or Ta. This is attributed to the hardening surface layer of the masks by nitradation, carbonization, or oxidation in CO/NH 3 gas plasma. This etching process is named as hardening mask etching. This etching process was also applied for tunneling magneto-resistive (TMR) multi-layers that uses magnetic random access memory with a Ta mask. A high anisotropy of about 80° was obtained without residues, sidewall deposition, and corrosion. This process is potentially applicable to the etching of thin magnetic materials in TMR stacks, patterned media, and read/write head.