High-density Plasma Production Research Articles

Development of a new J-PARC-made internal antenna for the J-PARC RF-driven H− ion source

We have been conducting the test of a new J-PARC-made internal antenna for the J-PARC RF-driven cesiated H− ion source. During the test of high-density plasma production by the antenna, we monitored the outgassing characteristics of the antenna by measuring the mass spectrum of the source gas and optical emission spectrum of the plasma. It is confirmed that no remarkable impurities were detected from the new antenna. The observed emittances of the H− beam extracted by using the new antenna were similar to those by using the SNS-made antenna. To accelerate the endurance test of the new antenna, we applied the antenna for the high-density plasma production to the 5% duty factor (1 ms pulse width with 50 Hz repetition rate) with the 2 MHz RF input power of approximately 60 kW at the ion source test stand. These values are much higher than those in the J-PARC nominal operation; 0.8 ms pulse width with 25 Hz repetition rate (the duty factor of 2%) with the RF input power of approximately 30 kW. The paper describes the results of the characteristics of the new J-PARC-made antenna.

PISCES-RF: a liquid-cooled high-power steady-state helicon plasma device

Radio-frequency (RF) driven helicon plasma sources can produce relatively high-density plasmas (n > 1019 m−3) at relatively moderate powers (<2 kW) in argon. However, to produce similar high-density plasmas for fusion relevant gases such as hydrogen (H), deuterium (D) and helium (He), much higher RF powers are needed. For very high RF powers, thermal issues of the RF-transparent dielectric window, used in the RF source design, limit the plasma operation timescales. To mitigate this constraint, we have designed, built and tested a novel helicon plasma source assembly with a fully liquid-cooled RF-transparent window which allows steady state operations at high power (up to 20 kW) and successfully produces high-density plasma with both argon and H. Deionized (DI) water, flowing between two concentric dielectric RF windows, is used as the coolant. We show that a full azimuthal blanket of DI water does not prevent high-density plasma production. From calorimetry on the DI water, we measure the net heat removed by the coolant at steady state conditions. Using infra-red imaging, we calculate the constant plasma heat deposition and measure the final steady state temperature distribution patterns on the inner surface of the ceramic layer. The heat deposition pattern follows the helical shape of the antenna. We also show the consistency between the heat absorbed by the DI water, as measured by calorimetry, and the total heat due to the combined effect of the plasma heating and the absorbed RF. These results are being used to answer critical engineering questions for the 200 kW RF device materials plasma exposure experiment being designed at the Oak Ridge National Laboratory as a next generation plasma material interaction device.

High-rate, room-temperature synthesis of amorphous silicon carbide films from organo-silicon in high-density helicon wave plasma

In this study, amorphous silicon carbide (α-SiC) films were synthesized on 316L stainless steel by low pressure, high density helicon wave plasma (HWP), using tetramethylsilane (TMS) as the single-source precursor which is organometallic compound. The influence of the substrate bias voltage (Vs) on the surface morphology, structure, chemical composition, and mechanical properties of the α-SiC films is investigated. The increase of VS from 0 to 200 V causes the removal of organic moieties from the film and results in the formation condition for α-SiC. The maximum deposition rate of the coating is up to 250 nm/s, which is related to the high-density (>1019 m−3) plasma production of HWP [1]. The X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared Spectrometer (FTIR) results imply that the film is mainly composed of SiC. The films deposited at VS = 200 V appear to be high-hardness (up to 33.6 GPa) materials with very small surface roughness (∼0.5 nm). Considering the easy control of the bias voltage, our work provides a new method for achieving α-SiC films with high-yield at room temperature.

High-Density Plasma Production in Converging Field Following a Magnetic Beach Plasma Source

High-Density Plasma Production in Converging Field Following a Magnetic Beach Plasma Source

Development of featured high-density helicon sources and their application to electrodeless plasma thruster

Helicon plasma sources using radio frequency (rf) waves are very useful, as they can produce high-density (∼1013 cm−3) plasma easily with a broad range of external operating parameters. Various kinds of featured helicon sources in a wide range of geometrical scales have been developed and characterized to control plasmas as required. Furthermore, particle production efficiency has demonstrated excellent performance over a very wide range of plasma sizes. High-beta (∼1) plasmas can also be easily achieved, showing the importance of the neutrals effect. As one of the many applications in areas ranging from fundamental to application fields, a space propulsion system with an advanced concept of an electrodeless condition (no direct contact between the plasma and electrodes/antennas) has been developed, owing to the expectation of a longer life operation. Among many proposals, two trials of electrodeless, additional acceleration methods are introduced, emphasizing the importance of some diagnostics. Here, we will review and describe the present status of our high-density rf plasma production with additional acceleration in an advanced propulsion field.

A concept of very high ratio gas compression device

A very high ratio gas compression device based on liquid metal conical implosion is described in this paper, which can reach a compression ratio up to 109–12. This device can produce extremely high density, high pressure, and high temperature, thermally equilibrated states by rapid but continuous compression of gaseous materials. The changes in the state parameters (temperature, pressure, density, radiation, line emission, Doppler broadening, dissociation, ionization) of the compressed material can be monitored over a very wide temperature range up to a million Kelvin. Potential applications of the device include many research fields such as chemical molecule property analyses, high density plasma production, high pressure physics, molecular and atomic physics, intermediate density nuclear fusion, sonoluminescence, etc.

Is the bulk mode conversion important in high density helicon plasma?

In a high-density helicon plasma production process, a contribution of Trivelpiece-Gould (TG) wave for surface power deposition is widely accepted. The TG wave can be excited either due to an abrupt density gradient near the plasma edge (surface conversion) or due to linear mode conversion from the helicon wave in a density gradient in the bulk region (bulk mode conversion). By numerically solving the boundary value problem of linear coupling between the helicon and the TG waves in a background with density gradient, we show that the efficiency of the bulk mode conversion strongly depends on the dissipation included in the plasma, and the bulk mode conversion is important when the dissipation is small. Also, by performing FDTD simulation, we show the time evolution of energy flux associated with the helicon and the TG waves.

Production of Low Electron-Temperature and High Density Plasma by Using a Grid-Cage Electrode for RF Discharge

Production of Low Electron-Temperature and High Density Plasma by Using a Grid-Cage Electrode for RF Discharge

High-Density Plasma Production in the GAMMA 10 Central Cell with ICRF Heating on Both Anchor Cells

In the GAMMA 10 tandem mirror, divertor simulation experiments that utilize particle flux toward the west end region (called end-loss flux) have been implemented. Since a positive correlation has been reported between the end-loss flux and the central-cell density, an increase of the central-cell density is important for obtaining a higher end-loss flux on the divertor simulation experiments. By arranging the ion cyclotron range of frequency (ICRF) systems so as to excite strong ICRF waves in both anchor cells simultaneously, we have succeeded in producing high-density plasmas (line density of 1.2 × 1014 cm−2) in both anchor cells. As a result, a higher central-cell density of 4.4 × 1012 cm−3 and a higher end-loss flux of more than 1023 m−2s−1 have been obtained. One of the possible mechanisms of the high density production is a formation of positive potentials on both anchor cells. Plasmas in the central cell are confined due to those potentials.

Carbon Ion Production Using a High-Power Impulse Magnetron Sputtering Glow Plasma

The ionization rate of sputtered carbon species in magnetron sputtering glow plasmas is low because of a low sputtering yield, a high ionization energy and a low reaction rate between the carbon and electron in the plasma. In this paper, efficient ionization of sputtered carbon species is realized in high-power impulse magnetron sputtering (HiPIMS) glow plasma. The arrangement of the permanent magnet placed at the back of the target can recover the above issues, which enables a power consumption as high as over 100 kW with a pulse duration as short as 5.5 μs at a source voltage as high as 2200 V. The magnet arrangement affects the production zone of the HiPIMS glow plasma on the target; the plasma moves outward to the radial direction of the target with an increased number of the inner magnets. When the plasma has a larger diameter on the target, a glow easily transits to an arc discharge even at a lower voltage compared with the case of the small-diameter plasma production, because the distance between the plasma and the grounded plate becomes short. Both the highest target voltage without an arc transition and the highest glow current are obtained at n=1, the least number of the inner magnet. In this case, a source voltage of 2200 V brings into the highest instantaneous power of about 144 kW. It is confirmed that higher the source voltage, higher the intensity of the optical emission spectrometry spectrum of carbon ions is. The high power consumption contributes to the high-density argon plasma production. Hence, the least number of the inner magnet results in a higher acceleration energy to bombard the target to efficiently sputter carbon species and a high ion flux bombarding to the target. The longer pulse duration such as 30 μs results in an arc transition at the source voltage as low as 1200 V. Thus, the highest emission intensity of the carbon optical emission obtained for n=1 at 2200 V with 5.5- μs pulse duration. It is observed that the intensities of the optical emission from argon and carbon ions are proportional to the power consumed in the plasma.

Production of High-Density Radio-Frequency Plasma Source by Ring-Shaped Hollow-Cathode Discharge at Various Trench Shapes

High-density radio-frequency (RF) plasma sources have been produced by ring-shaped hollow-cathode discharge at various trench shapes. The influence of hollow-cathode trench shape on high-density plasma production has been investigated at a wide range of argon gas pressure and various input powers. The trench shapes are selected from well-typed, taper-typed, step-typed, and three improved step-typed trench shapes. It is revealed that, at the lower pressure less than 200 mtorr, the plasma density for the well-typed shape is the highest among the three shapes, while for the step-typed shape, it is the lowest. For the higher pressure more than 200 mtorr, the plasma density for the step-typed shape has the highest value. The results indicate that the plasma density for all typed shapes is almost proportional to RF input power. It is found that the improved step-typed trench shapes can attain a wide range of gas pressure sustaining higher plasma density.

Studies on High Density Plasma Production and Neutral Pressure Control for a Cusp-Type Direct Energy Converter Simulator

As for charge separation capability of cusp-type direct energy converter (CuspDEC), which is expected to be used in an advanced fusion, high density plasma production has been studied with keeping a collision-less condition of the cusp region. Using a pulsed feeding technique, high density plasma production has been achieved and low gas pressure enough to keep collision-less condition has been evaluated by a simple gas dynamics calculation.

Criteria of radio-frequency ring-shaped hollow cathode discharge using H2 and Ar gases for plasma processing

In order to achieve high-density capacitively coupled plasma, a radio-frequency (RF) ring-shaped hollow cathode discharge has been developed as a candidate for processing plasma sources. The plasma density in the hollow cathode discharge reaches a high magnitude of 1010–1011 cm−3. The RF ring-shaped hollow cathode discharge depends on the pressure and mass of the working gas. Criteria required for producing a RF ring-shaped hollow cathode discharge have been investigated for various gas pressures using H2 and Ar gases for high-density plasma production. The results reveal that the criteria for the occurrence of the hollow cathode effect are that the trench width should be approximately equal to the sum of the electron-neutral mean free paths and twice the sheath thickness of the RF powered electrode.

Utilizing upper hybrid resonance for high density plasma production and negative ion generation in a downstream region

Localized wave-induced resonances are created by microwaves launched directly into a multicusp (MC) plasma device in the k ⊥ B mode, where k is the wave vector and B is the static magnetic field. The resonance zone is identified as upper hybrid resonance (UHR), and lies r = ∼22 mm away from the MC boundary. Measurement of radial wave electric field intensity confirms the right hand cutoff of the wave (r = 22.5–32.1 mm) located near the UHR zone. A sharp rise in the corresponding electron temperature in the resonance region by ∼13 eV from its value away from resonance at r = 0, is favorable for the generation of vibrationally excited molecules of hydrogen. A transverse magnetic filter allows cold electrons (∼1–2 eV) to pass into the downstream region where they generate negative ions by dissociative attachment. Measurements of electron energy distribution function (EEDF) support the viewpoint. H− current density of ∼0.26 mA/cm2 is obtained at a wave power density of ∼3 W/cm2 at 2.0 mTorr pressure, which agrees reasonably well with results obtained from a steady state model using particle balance equations.

New oxygen radical source using selective sputtering of oxygen atoms for high rate deposition of TiO2 films

We have developed a new oxygen radical source based on the reactive sputtering phenomena of a titanium target for high rate deposition of TiO2 films. In this oxygen radical source, oxygen radicals are mainly produced by two mechanisms: selective sputter-emission of oxygen atoms from the target surface covered with a titanium oxide layer, and production of high-density oxygen plasma in the space near the magnetron-sputtering cathode. Compared with molecular oxygen ions, the amount of atomic oxygen radicals increased significantly with an increase in discharge current so that atomic oxygen radicals were mainly produced by this radical source. It should be noted that oxygen atoms were selectively sputtered from the target surface, and titanium atoms sputter-emitted from the target cathode were negligibly small. The amount of oxygen radicals supplied from this radical source increased linearly with increasing discharge current, and oxygen radicals of 1 × 1015 atoms/s/cm2 were supplied to the substrate surface at a discharge current of 1.2 A. We conclude that our newly developed oxygen radical source can be a good tool to achieve high rate deposition and to control the structure of TiO2 films for many industrial design applications.

Production of high-density high-temperature plasma by collapsing small solid-density plasma shell with two ultra-intense laser pulses

Three-dimensional particle-in-cell simulations show that the anisotropic collapse of a plasma microshell by impact of two oppositely directed intense laser pulses can create at the center of the shell cavity a submicron-sized plasma of high density and temperature suitable for generating fusion neutrons.

Formation of dust in low-pressure magnetized hydrocarbon plasmas

The rapid formation of large molecules and the subsequent production of solid-state dust particles in a low-pressure discharge is unlikely, because of the low rates of the polymerization reactions and short lifetimes of the species. Here, we suggest that C dust particles can form in atypically low (10− 3 mbar)-pressure hydrocarbon plasmas if the dust charging time is much shorter than the gas residence time in the device; we present supporting experimental evidence for this. Such a condition can be obtained by the production of high-density plasmas. The results show that dust formation from the gaseous phase can occur in a much wider parameter range than is commonly assumed.

A compact ellipsoidal cavity type microwave plasma reactor for diamond film deposition

Electric field distribution in ellipsoidal microwave cavities with different sizes was modeled by the finite difference time-domain method (FDTD). The influence of varying size on the performance of the ellipsoidal cavities was studied. Through the simulations, eight series of resonant patterns were found. Based on this simulation result, a compact ellipsoidal cavity type microwave plasma chemical vapor deposition reactor has been proposed and its performance was predicted. It is shown that such a compact ellipsoidal cavity type reactor retains the same ability to concentrate microwave energy into its focus, facilitating both production of high density plasmas and deposition of diamond films.

Production of high-density radiofrequency plasma under a divergent magnetic field provided by permanent magnets

Production of high-density radiofrequency plasma under a divergent magnetic field provided by permanent magnets

High Density Plasma Production with Phase Controlled ICRF Antennas in the Gamma-10 Central Cell

This manuscript reports the high density plasma production with a pair of phase controlled ion-cyclotron range of frequency antennas in GAMMA 10. For the plasma production, the Radio Frequency (RF) power (~10 MHz) is coupled to the fast Alfvén wave in the central cell. The antenna-plasma coupling depends strongly on the antenna structure. In this study, according to the numerical prediction, a pair of double half-turn and Nagoya Type-III antennas is adopted for the excitation of the fast wave. The antennas are driven at the same frequency with controlling their phase difference. It is observed that an optimum phase difference exists in the present density range. The density increases with the RF power and the gas-fuelling rate, when the phase difference is set to the optimum value. The considerable increase in the density was obtained up to twice as large as the conventional value.