Study of plasma parameters of coaxial plasma source using triple Langmuir probe and Faraday cup diagnostics

Coaxial plasma guns are a type of plasma source that produces plasma which propagates radially and axially controlled by the shape of the ground electrode, which has attracted much interest in several applications. In this work, a 120° opening angle of CPG nozzle is used as a plasma gun configuration that operates at the energy of 150 J. The ionization of polyethylene insulator between the electrodes of the gun produces a cloud of hydrogen and carbon plasma.The triple Langmuir probe and Faraday cup are used to measure plasma density and plasma temperature. These methods are used to measure the on-axis and off-axis plasma divergence of the coaxial plasma gun. The peak values of ion densities measured at a distance of 25 mm on-axis from the plasma gun are(1.6±0.5)×10^(19)m^(-3)and(2.8±0.6)×10^(19)m^(-3)for hydrogen and carbon plasma respectively and the peak temperature is 3.02±0.5 eV. The mean propagation velocity of plasma is calculated using the transit times of plasma at different distances from the plasma gun and is found to be 4.54±0.25 cm/μs and 1.81±0.18 cm/μs for hydrogen and carbon plasma respectively. The Debye radius is obtained from the measured experimental data that satisfies the thin sheath approximation. The shot-to-shot stability of plasma parameters facilitates the use of plasma guns in laboratory experiments. These types of plasma sources can be used in many applications like plasma opening switches, plasma devices, and as plasma sources.

Finite element analysis of keyhole plasma arc welding based on an adaptive heat source mode

An adaptive heat source mode is proposed to account for the keyhole effect and the characteristics of volumetric distribution along the direction of the workpiece thickness. Finite element analysis of the temperature field in keyhole plasma arc welding is conducted and the weld geometry is obtained. The predicted results are in agreement with the measured ones.

Diagnosis of Hydrogen Plasma in a Miniature Penning Ion Source by Double Probes

Parameters of hydrogen plasma in a miniature Penning discharge ion source, including the electron temperature and the electron density, were measured by using double probes. The results indicate that the electron density increases and the electron temperature decreases with the increase in gas pressure and the discharge current. The electron temperature is about 5 - 9 eV and the electron density is 6.0× 10^13 ～ 1.2 × 10^14 m^-3 while the discharge current is in a range of 50 - 120 μA.

Interaction between plasma and electromagnetic field in ion source of 10 cm ECR ion thruster

Through diagnosing the plasma density and calculating the intensity of microwave electric field,four 10 cm electron cyclotron resonance(ECR)ion sources with different magnetic field structures are studied to reveal the inside interaction between the plasma,magnetic field and microwave electric field.From the diagnosing result it can be found that the plasma density distribution is controlled by the plasma generation and electron loss volumes associated with the magnetic field and microwave power level.Based on the cold plasma hypothesis and diagnosing result,the microwave electric field intensity distribution in the plasma is calculated.The result shows that the plasma will significantly change the distribution of the microwave electric field intensity to form a bow shape.From the boundary region of the shape to the center,the electric field intensity varies from higher to lower and the diagnosed density inversely changes.If the bow and its inside lower electric field intensity region are close to the screen grid,the performance of ion beam extracting will be better.The study can provide useful information for the creating of 10 cm ECR ion source and understanding its mechanism.

Development of Powerful RF Plasma Sources for Present and Future NBI Systems

This paper deals with the topic of RF plasma sources and their application inhigh-power neutral beam heating systems for nuclear fusion devices. RF sources represent aninteresting alternative to the conventional arc discharge sources. Due to the absence of hotfilaments they exhibit an inherent simplicity both in mechanical and electrical aspects andconsequently offer advantages in terms of cost savings, gain in availability and reliability andreduced maintenance. This renders the RF plasma source attractive for any long pulse (> 10 sec) NBIsystem and in particular for the ITER NBI system. The latter, however, requires that the RF plasmasource is also capable of delivering negative rather than positive hydrogen ions. In the first partof the paper the types, characteristics and operation experience of RF plasma sources for positiveions in operation are described. The second part is devoted to the development for ITER NBI: thebasic requirements, physics and technology issues and the present status are discussed.

Experimental Study of a Minitype Atmospheric Non-equilibrium Plasma Source

A mini-type of plasma source was studied experimentally. The results showed that the plasma density, which was generated by an atmospheric non-equilibrium plasma source, rises with the increase in driving electric-field and the momentum of gas particles. For a driving electricfield of 56 kV/cm and a gas particles＇ momentum of 10^9 × 10^-22 g·m/s, the ion density can exceed 10^10/cm^3 while the effective volume of the plasma source is only 2.5 cm^2. This study may help develop a method to generate a minitype plasma source with low energy consumption but high ion concentration. This source can be used in chemical industry, environmental engineering and military applications.

Oxide Coated Cathode Plasma Source of Linear Magnetized Plasma Device

Plasma source is the most important part of the laboratory plasma platform for fundamental plasma experimental research. Barium oxide coated cathode plasma source is well recognized as an effective technique due to its high electron emission current. An indirectly heated oxide coated cathode plasma source has been constructed on a linear magnetized plasma device. The electron emission current density can reach 2 A/cm2 to 6 A/cm2 in pulsed mode within pulse length 5-20 ms. A 10 cm diameter, 2 m long plasma column with density 10is m-3 to 1019 m3 and electron temperature Te --~ 3-7 eV is produced. The spatial uniformity of the emission ability is less than 4% and the discharge reproducibility is better than 97%. With a wide range of the plasma parameters, this kind of plasma source provides great flexibility for many basic plasma investigations. The detail of construction and initial characterization of oxide coated cathode are described in this paper.

Linear Plasma Sources for Large Area Film Deposition:A Brief Review

By utilization of different excitation power sources, linear plasma sources can be differentiated into DC, RF, VHF, microwave and dual frequency types. Through installing several linear plasma sources in parallel or adopting the so-called roll-to-roll （air-to-air） process, scale uniform linear plasma sources were realized and successfully applied to the deposition of large area uniform dielectric thin films, Furthermore, the magnetic field system can effectively reduce the recombination losses on the wall of the vacuum chamber and enhance the plasma density. Linear plasma sources with approximately one square meter deposition area with the plasma density of 1011 cm 3 have been developed, some of which have been used for the deposition of dielectric layers and large area plasma etching.

Laser-produced plasma helium-like titanium Kα x-ray source and its application to Rayleigh-Taylor instability study

Several experiments are performed on the ShenGuang-Ⅱ laser facility to investigate an x-ray source and test radiography concepts. X-ray lines emitted from laser-produced plasmas are the most practical means of generating these high intensity sources. By using a time-integrated space-resolved keV spectroscope and pinhole camera, potential helium-like titanium Kα x-ray backlighting （radiography） line source is studied as a function of laser wavelength, ratio of pre-pulse intensity to main pulse intensity, and laser intensity （from 7.25 to ～ 11.3 × 10^15 W/cm2）. One-dimensional radiography using a grid consisting of 5 #m Au wires on 16 μm period and the pinhole-assisted point projection is tested. The measurements show that the size of the helium-like titanium Ka source from a simple foil target is larger than 100 ~m, and relative x-ray line emission conversion efficiency ~x from the incident laser light energy to helium- like titanium K-shell spectrum increases significantly with pre-pulse intensity increasing, increases rapidly with laser wavelength decreasing, and increases moderately with main laser intensity increasing. It is also found that a gold gird foils can reach an imaging resolution better than 5-μm featured with high contrast. It is further demonstrated that the pinhole-assisted point projection at such a level will be a novel two-dimensional imaging diagnostic technique for inertial confinement fusion experiments.

Plasma density measurement and downstream etching of silicon and silicon oxide in Ar/NF3 mixture remote plasma source

In this study,plasma density measurements were performed near the plume region of the remote plasma source (RPS) in Ar/NF3 gas mixtures using a microwave cutoff probe.The measured plasma density is in the range of 1010-1011 cm-3 in the discharge conditions with RPS powers of 2-4 kW and gas pressures of 0.87-4 Torr.The plasma density decreased with increasing gas pressures and RPS powers under various Ar/NF3 mixing ratios.This decrease in the plasma density measured at the fixed measurement position (plume region) can be understood by the reduction of the electron energy relaxation length with increases in the gas pressures and mixing ratio of NF3/(Ar/NF3).We also performed downstream etching of silicon and silicon oxide films in this system.The etch rate of the silicon films significantly increases while the silicon oxide is slightly etched with the gas pressures and powers.It was also found that the etch rate strongly depends on the wafer position on the processing chamber electrode,and that the etch selectivity reached 96-131 in the discharge conditions of RF powers (3730-4180 W) and gas pressures (3.6-4 Torr).

Development of plasma sources for Dipole Research EXperiment(DREX)

Dipole Research EXperiment（DREX） is a new terrella device as part of the Space Plasma Environment Research Facility（SPERF） for laboratory studies of space physics relevant to the inner magnetospheric plasmas. Adequate plasma sources are very important for DREX to achieve its scientific goals. According to different research requirements, there are two density regimes for DREX. The low density regime will be achieved by an electron cyclotron resonance（ECR） system for the ‘whistler/chorus＇ wave investigation, while the high density regime will be achieved by biased cold cathode discharge for the desired ‘Alfvén＇ wave study. The parameters of ‘whistler/chorus＇ waves and ‘Alfvén＇ waves are determined by the scaling law between space and laboratory plasmas in the current device. In this paper, the initial design of these two plasma sources for DREX is described. Focus is placed on the chosen frequency and operation mode of the ECR system which will produce relatively low density ‘artificial radiation belt＇ plasmas and the seed electrons, followed by the design of biased cold cathode discharge to generate plasma with high density.

Experimental investigation of laser-produced-plasma EUV source based on liquid target

A laser-produced plasma(LPP) source was built using liquid as target and a Nd:YAG laser as the irradiation laser, and the LPP source's radiation with ethanol and acetone target respectively was measured by an AXUV100 silicon photodiode combined with a McPHERSON model 247 grazing incidence monochromator of the resolution Δλ≤0.075 nm and the wavelength scanning interval 0.5 nm. Both ethanol and acetone target LPP source had EUV emission at 11～20 nm wavelength. The comparison between the spectra of the two kinds of target materials shows that all the two kinds of target source's spectra are the result of oxygen ions' transitions under current source's parameters, but the spectrum intensity from different target sources is different. The spectra intensity from the ethanol target is higher than that from the acetone target. In addition, the target liquid is forced into the vacuum chamber by the background pressure supported by the connected external high pressure gas, and the influence of the background pressure on the source's intensity is investigated.

Comparison of different plasma chambers in microwave ion source for the intense neutron tube

The microwave absorption efficiency, which is relevant to magnet field and its distribution, is a major parameter of the microwave ion source (MWIS) for the intense neutron tube. Based on previous work, the relations between microwave absorption efficiency and plasma chamber structure and thickness of the microwave introduction window are studied. The microwave absorption efficiency reaches to 100% when plasma chamber is 100mm long and the window thickness is 30mm. The microwave absorption efficiency as a function of pressure is also presented.

Temperature elevated N ion implantation of Ti6A14V alloys using the plasma source

Specimens of Ti6A14V alloy were implanted with nitrogen ions of 4× 1018 cm-2 at temperatures from 100 to 600℃. Auger Electron Spectroscopy (AES), microhardness measurements and pin-on-disk wear testing, Scanning Electron Mi- croscopy (SEM), and Glancing angle X-ray Diffraction. (XRD) were utilized to evaluate the surface property improvements. The thickness of implanted layers increased by about an order of magnitude when the temperature was elevated from 100 to 6000℃. Higher surface hardness and wear resistance were also obtained in the high tempera-ture implantation. The XRD image showed the presence of nitrides of titanium at the implanted surface.

X－Ray from Laser Produced Plasma as an Excitation Source in Spectroscopy Study

Spectral and temporal characteristics of soft X-ray from the laser-produced plasma (LPX)were studied under different conditions.The obtained LPX spectrum showed a little different from the black-body distribution in some other references,which is analysed theoretically.It is shown that LPX can be used as a convenient exciting method in spectroscopy study.

The Gridless Plasma Ion Source (GIS)for Plasma Ion Assisted Optical Coating

High-quality optical coating is a key technology for modern optics. lon-assisted deposition technology was used to improve the vaporized coating in 1980's. The GIS (gridless ion source), which is an advanced plasma source for producing a high-quality optical coating in large area, can produce a large area uniformity>1000 mm(diameter), a high ion current density - 0.5mA/cm2, 20 eV - 200 eV energetic plasma ions and can activate reactive gas and film atoms. Now we have developed a GIS system. The GIS and the plasma ion-assisted deposition technology are investigated to achieve a high-quality optical coating. The GIS is a high power and high current source with a power of l kW - 7.5 kW, a current of 10 A - 70 A and an ion density of 200 μA/cm2 - 500 μA/cm2. Because of the special magnetic structure, the plasma-ion extraction efficiency has been improved to obtain a maximum ion density of 500 μA/cm2 in the medium power (- 4kW) level. The GIS applied is of a special cathode structure, so that the GIS operation can be maintained under a rather low power and the lifetime of cathode will be extended. The GIS has been installed in the LPSX-1200 type box coating system. The coated TiO2, SiO2 films such as antireflective films with the system have the same performance reported by Leybold Co, 1992, along with a controllable refractive index and film structure.

Performance of a New Ion Source for KSTAR Tokamak Plasma Heating

In the experimental campaign of 2010 and 2011 on KSTAR, the NBI-1 system was equipped with one prototype ion source and operated successfully, providing a neutral beam power of 0.7-1.6 MW to the tokamak plasma. The new ion source planned for the 2012 KSTAR campaign had a much more advanced performance compared with the previous one. The target performance of the new ion source was to provide a neutral deuterium beam of 2 MW to the tokamak plasma. The ion source was newly designed, fabricated, and assembled in 2011. The new ion source was then conditioned up to 64 A/100 keV over a 2-hour beam extraction and performance tested at the NB test stand （NBTS） at the Korea Atomic Energy Research Institute （KAERI） in 2012. The measured optimum perveance at which the beam divergence is a minimum was about 2.5μP, and the minimum beam divergent angle was under 1.0° at 60 keV. These results indicate that the 2.0 MW neutral beam power at 100 keV required for the heating of plasma in KSTAR can be delivered by the installation of the new ion source in the KSTAR NBI-1 system.

Low Energy Plasma Focus as an Intense X-ray Source for Radiography

Study on X-ray emission from a low energy (1.8 kJ) plasma focus devicepowered by a 9 μF capacitor bank, charged at 20 kV and giving peak discharge current of about 175kA by using a lead-inserted copper-tapered anode is reported. The X-ray yield in different energywindows is measured as a function of hydrogen filling pressure. The maximum yield in 4π-geometry isfound to be (27.3+-1.1) J and corresponding wall plug efficiency for X-ray generation is 1.52+-0.06%. X-ray emission, presumably due to bombarding activity of electrons in current sheath at theanode tip was dominant, which is confirmed by the pinhole images. The feasibility of the device asan intense X-ray source for radiography is demonstrated.

Two-dimensional particle-in-cell plasma source ion implantation of a prolate spheroid target

A two-dimensional particle-in-cell simulation is used to study the time-dependent evolution of the sheath surrounding a prolate spheroid target during a high voltage pulse in plasma source ion implantation. Our study shows that the potential contour lines pack more closely in the plasma sheath near the vertex of the major axis, i.e. where a thinner sheath is formed, and a non-uniform total ion dose distribution is incident along the surface of the prolate spheroid target due to the focusing of ions by the potential structure. Ion focusing takes place not only at the vertex of the major axis, where dense potential contour lines exist, but also at the vertex of the minor axis, where sparse contour lines exist. This results in two peaks of the received ion dose, locating at the vertices of the major and minor axes of the prolate spheroid target, and an ion dose valley, staying always between the vertices, rather than at the vertex of the minor axis.

Atomic-Oxygen Beam Source with Compact ECR Plasma

An atomic-oxygen beam source with compact ECR plasma was successfully investigated. The microwave was produced and transmitted in a coaxial mode, and coupled with the loop. The plasma was produced at a higher asymmetry magnetic mirror field, and neutralized with the molybdenum target at a lower asymmetry magnetic mirror field. The magnetic field was constituted with permanent magnets. This source has a higher flux density of atom beam, a lower operating pressure, a smaller power consumption and low-cost. When it was installed at the equipment to study the interaction of the beam with the surface, the operation was carried out very easily and with a good stability.