Deposition of Diamond-Like Carbon on Inner Surface by Hollow Cathode Discharge

A cylindrical hollow cathode discharge （HCD） in CH4/Ar gas mixture at pressure of 20-30 Pa was used to deposit diamond-like carbon （DLC） films on the inner surface of a stainless steel tube. The characteristics of the HCD including the voltage-current curves, the plasma im- ages and the optical emission spectrum （OES） were measured in Ar and CHn/Ar mixtures. The properties of DLC films prepared under different conditions were analyzed by means of Raman spectroscopy and scanning electron microscopy （SEM）. The results show that the electron exci- tation temperature of HCD plasma is about 2400 K. DLC films can be deposited on the inner surface of tubes. The ratio of sp3/sp2 bonds decreases with the applied voltage and the deposition time. The optimizing CH4 content was found to be around CH4/Ar =1/5 for good quality of DLC films in the present system.

The Effect of Gas Flow Rate on Radio-Frequency Hollow Cathode Discharge Characteristics

It is known that gas flow rate is a key factor in controlling industrial plasma processing. In this paper, a 2D PIC/MCC model is developed for an rf hollow cathode discharge with an axial nitrogen gas flow. The effects of the gas flow rate on the plasma parameters are calculated and the results show that： with an increasing flow rate, the total ion（N＋2, N＋） density decreases, the mean sheath thickness becomes wider, the radial electric field in the sheath and the axial electric field show an increase, and the energies of both kinds of nitrogen ions increase;and, as the axial ion current density that is moving toward the ground electrode increases, the ion current density near the ground electrode increases. The simulation results will provide a useful reference for plasma jet technology involving rf hollow cathode discharges in N2.

Determinations of plasma density and decay time in the hollow cathode discharge by microwave transmission

The microwave （MW） transmission method is employed to measure both the plasma density and the plasma decay time in the hollow cathode discharge （HCD） in argon at low pressure. The plasma density in DC-driven or pulsed HCD is on the order of 1012 cm-3, which can block the X-band MW effectively. In the case of pulsed HCD, the MW transmittance shows the same waveform as the pulsed current during the rising edge if the driving frequency is low, but with a longer delay during the falling edge. The MW transmittance reaches a constant low level when the driving frequency is high enough. The plasma decay time in the HCD system is measured to be about 100 μs around a pressure of 120 Pa. The ambipolar diffusion is considered to be the major mechanism in the decay process.

PIC/MCC Simulation of Radio Frequency Hollow Cathode Discharge in Nitrogen

A two-dimensional PIC/MCC model is developed to simulate the nitrogen radio frequency hollow cathode discharge（rf-HCD）.It is found that both the sheath oscillation heating and the secondary electron heating together play a role to maintain the rf-HCD under the simulated conditions.The mean energy of ions（N＋_2,N＋）in the negative glow region is greater than the thermal kinetic energy of the molecular gas（N2）,which is an important characteristic of rf-HCD.During the negative portion of the hollow electrode voltage cycle,electrons mainly follow pendulum movement and produce a large number of ionization collisions in the plasma region.During the positive voltage of the rf cycle,the axial electric field becomes stronger and its direction is pointing to the anode（substrate）,therefore the ions move toward the anode（substrate）via the axial electric field acceleration.Compared with dc-HCD,rf-HCD is more suitable for serving as a plasma jet nozzle at low pressure.

A N_2 Plasma Light Source Generated in Hollow Cathode Discharge and Its Application in Lithographic Plate Making

Computer to conventional plate （CTCP） technology is getting more and more attention in printing industries. In this paper we report a nitrogen plasma light source generated in hollow cathode discharge （HCD）, Which is used for pre-sensitivity （PS） plate exposure. The N2 molecule emits abundant spectrum ranging from 350 nm to 460 nm. With the voltage of 580 V, current of 1.8 A and pressure of 70 Pa in the discharge an optical power density of 0.46 mW/cm2 is obtained. The optical power density could be further increased with optimizing the lens system. The phototonus efficiency of this source is discussed in detail based upon the chemical principle and the FTIR analysis on the coating material.

Experimental Study on RF Hollow Cathode Discharge

By using a longitudinal static magnetic field, we have shown that it is possible to excite an intensive plasma in a simple stainless steel tube which is connected with a RF power supply. Under certain conditions, the very bright Ar II lines were excited. The emission intensities of Ar II lines were increased with the increase in RF power, magnetic field, and the decrease in argon pressure. As the plasma-sheath boundary oscillating under the RF voltage, the plasma column is periodically compressed by the oscillating boundary.

Effects of discharge parameters on the micro-hollow cathode sustained glow discharge

The effects of parameters such as pressure,first anode radius,and the cavity diameter on the micro-hollow cathode sustained glow discharge are investigated by using a two-dimensional self-consistent fluid model in pure argon.The results indicate that the three parameters influence the discharge in the regions inside and outside of the cavity.Under a fixed voltage on each electrode,a larger volume of high density plasma can be produced in the region between the first and the second anodes by selecting the appropriate pressure,the higher first anode,and the appropriate cavity diameter.As the pressure increases,the electron density inside the hollow cathode,the high density plasma volume between the first anode and second anodes,and the radial electric field in the cathode cavity initially increase and subsequently decrease.As the cavity diameter increases,the high-density plasma volume between the first and second anodes initially increases and subsequently decreases;whereas the electron density inside the hollow cathode decreases.As the first anode radius increases,the electron density increases both inside and outside of the cavity.Moreover,the increase of the electron density is more obvious in the microcathode sustained region than in the micro cavity region.The results reveal that the discharge inside the cavity interacts with that outside the cavity.The strong hollow cathode effect and the high-density plasma inside the cavity favor the formation of a sustained discharge between the first anode and the second anodes.Results also show that the radial boundary conditions exert a considerably weaker influence on the discharge except for a little change in the region close to the radial boundary.

Microstructure and Deuterium Retention of Tungsten Deposited by Hollow Cathode Discharge in Deuterium Plasma

Tungsten has been chosen as one of the most promising candidates as the plasma-facing material in future fusion reactors. Although tungsten has numerous advantages compared with other materials, issues including dust are rather difficult to deal with. Dust is produced in fusion devices by energetic plasma-surface interaction. The re-deposition of dust particles could cause the retention of fuel atoms. In this work, tungsten is deposited with deuterium plasma by hollow cathode discharge to simulate the dust production in a tokamak. The morphology of the deposited tungsten can be described as a film with spherical particles on it. Thermal desorption spectra of the deposited tungsten show extremely high desorption of the peak positions. It is also found that there is a maximum retention of deuterium in the deposited tungsten samples due to the dynamic equilibrium of the deposition and sputtering process on the substrates.

Best Magnetic Condition to Generate Hollow Cathode Glow Plasma in High Vacuum

Based on magnetron hollow cathode discharge, the magnetic condition of glow plasma generation in high vacuum, including both direction and magnitude of the applied mag- netic field, is theoretically derived and experimentally evaluated in this paper. Single particle orbital theory is introduced to discuss the possibilities to generate glow plasma at gas pressure under 10-2 Pa when the magnetic field direction is parallel or perpendicular or oblique to the electric field direction. A quantitative estimation criterion of magnetic induction intensity is also proposed in theory. The comparison with experiments suggests that glow plasma in high vacuum will form more easily in oblique magnetic field condition and that the criterion is accurate enough to estimate magnetic induction intensity at a certain gas pressure.

The Interaction of C-Band Microwaves with Large Plasma Sheets

A large plasma sheet 60 cm×60 cm×2 cm in size was generated using a hollow cathode, and measurements were conducted for interactions including transmission, reflection and absorption. With different discharge parameters, plasma sheets can vary and influence microwave strength. Microwave reflection decreases when the discharge current rises, and the opposite occurs in transmission. The C-band microwave is absorbed when it is propagated through large plasma sheets at higher pressure. When plasma density and collision frequency are fitted with incident microwave frequency, a large amount of microwave energy is consumed. Reflection, transmission and absorption all exist simultaneously. Plasma sheets are an attractive alternative to microwave steering at low pressure, and the microwave reflection used in receiving radar can be altered by changing the discharge parameters.

Different Shapes of Nano-ZnO Crystals Grown in Catalyst-Free DC Plasma

Nano-ZnO crystals grown in hollow-cathode discharge （HCD） driven by direct current （DC） power on p-silicon （100） substrates were presented. With Ar as the diluted gas, 02 as the reactive gas and high purity zinc powder as the metallic source, the nano-ZnO structure was grown in a catalyst-free process. The crystal ZnO morphology was measured by scanning electron microscopy （SEM）. Photoluminescence （PL） spectroscopy was employed to evaluate the crystal nano-ZnO＇s properties. Effect of several parameters, such as the temperature, 02 ratio, deposition time and polarity during nanostructure growth, was also investigated.

Discharge characteristics of the DUHOCAMIS with a high magnetic bottle-shaped field

For the purpose of producing high intensity, multiply charged metal ion beams, the dual hollow cathode ion source for metal ions （DUHOCAMIS） was derived from the hot cathode Penning ion source combined with the hollow cathode sputtering experiments in 2007. To investigate the behavior of this discharge geometry in a stronger magnetic bottle-shaped field, a new test bench for DUHOCAMIS with a high magnetic bottle-shaped field up to 0.6 T has been set up at the Peking University. The experiments with magnetic fields from 0.13 T to 0.52 T have indicated that the discharge behavior is very sensitive to the magnetic flux densities. The slope of discharge curves in a very wide range can be controlled by changing the magnetic field as well as regulated by adjusting the cathode heating power; the production of metallic ions would be much greater than gas ions with the increased magnetic flux density; and the magnetic field has a much higher influence on the DHCD mode than on the PIG mode.