Simulation study on the influence of magnetic field in the near-anode region on anode power deposition of ATON-type Hall thruster

The highest deposition of power and temperature is always near the cusp of the ATON-type Hall thruster.This shows that when there are electrons gathering at the cusp,the distribution of heat load will be uniform,which will potentially damage the reliability.Therefore,we optimize the magnetic field near the anode.We changed the magnetic field characteristics in the near-anode region with an additional magnetic screen,and performed numerical simulation with particle-incell simulation.The simulation results show that the magnetic field of the thruster with the additional magnetic screen can alleviate the over-concentration of power deposition on the anode and reduce the power deposition in the anode by 20%,while ensuring that the overall magnetic field characteristics do not change significantly.

Energy dissipation and power deposition of electromagnetic waves in the plasma sheath

Energy dissipation and power deposition of electromagnetic waves(EMW)in the reentry plasma sheath provide an opportunity to investigate‘communication blackout’phenomena.Based on afinite element method(FEM)simulation,we analyze variation of EMW energy dissipation and power deposition profiles dependent on the wave polarization,wave incident angle,plasma density profile and electron collision frequency.Cutoff and resonance of EMW in the plasma sheath are crucial in explaining the regulation of energy dissipation and power deposition.

Influence of magnetic field on power deposition in high magnetic field helicon experiment

Based on high magnetic field helicon experiment(HMHX), HELIC code was used to study the effect of different magnetic fields on the power deposition under parabolic distribution. This paper is divided into three parts: preliminary calculation, actual discharge experiment and calculation. The results of preliminary calculation show that a magnetic field that is too small or too large cannot produce a good power deposition effect. When the magnetic field strength is 1200 Gs,a better power deposition can be obtained. The actual discharge experiment illustrates that the change of the magnetic field will have a certain influence on the discharge phenomenon. Finally, the results of verification calculation successfully verify the accuracy of the results of preliminary simulation. The results show that in the actual discharge experiment, it can achieve the best deposition effect when the magnetic field is 1185 Gs.

Diagnosis of gas phase near the substrate surface in diamond film deposition by high-power DC arc plasma jet CVD

Optical emission spectroscopy （OES） was used to study the gas phase composition near the substrate surface during diamond deposition by high-power DC arc plasma jet chemical vapor deposition （CVD）. C2 radical was determined as the main carbon radical in this plasma atmosphere. The deposition parameters, such as substrate temperature, anode-substrate distance, methane concentration, and gas flow rate, were inspected to find out the influence on the gas phase. A strong dependence of the concentrations and distribution of radicals on substrate temperature was confirmed by the design of experiments （DOE）. An explanation for this dependence could be that radicals near the substrate surface may have additional ionization or dissociation and also have recombination, or are consumed on the substrate surface where chemical reactions occur.

Effect of a negative DC bias on a capacitively coupled Ar plasma operated at different radiofrequency voltages and gas pressures

The effect of a negative DC bias,|V_(dc)|,on the electrical parameters and discharge mode is investigated experimentally in a radiofrequency(RF)capacitively coupled Ar plasma operated at different RF voltage amplitudes and gas pressures.The electron density is measured using a hairpin probe and the spatio-temporal distribution of the electron-impact excitation rate is determined by phase-resolved optical emission spectroscopy.The electrical parameters are obtained based on the waveforms of the electrode voltage and plasma current measured by a voltage probe and a current probe.It was found that at a low|V_(dc)|,i.e.inα-mode,the electron density and RF current decline with increasing|V_(dc)|;meanwhile,the plasma impedance becomes more capacitive due to a widened sheath.Therefore,RF power deposition is suppressed.When|V_(dc)|exceeds a certain value,the plasma changes toα–γhybrid mode(or the discharge becomes dominated by theγ-mode),manifesting a drastically growing electron density and a moderately increasing RF current.Meanwhile,the plasma impedance becomes more resistive,so RF power deposition is enhanced with|V_(dc)|.We also found that the electrical parameters show similar dependence on|V_(dc)|at different RF voltages,andα–γmode transition occurs at a lower|V_(dc)|at a higher RF voltage.By increasing the pressure,plasma impedance becomes more resistive,so RF power deposition and electron density are enhanced.In particular,theα–γmode transition tends to occur at a lower|V_(dc)|with increase in pressure.

Longitudinal impedance measurements and simulations of a three-metal-strip kicker

A kicker is a critical component for beam injection and accumulation in circular particle accelerators. A ceramic slat kicker plated with a TiN conductive coating was applied in the Beijing Electron Positron Collider (BEPCII). However, the ceramic slat kicker has experienced several sudden malfunctions during the operation of the BEPCII in the past. With a reliable kicker structure, a three-metal-strip kicker can substitute the original ceramic slat kicker to maintain the operational stability of the BEPCII. A comparison of the numerical simulation was conducted for three kicker models, demonstrating the comprehensive advantage of the three-metal-strip kicker. Furthermore, impedance bench measurements were conducted on a prototype of a three-metal-strip kicker. The longitudinal beam-coupling impedance was measured using a vector network analyzer via the coaxial wire method. A satisfactory agreement was obtained between the numerical simulations and measurements. Based on the numerical simulation data, the loss factor was 0.01721 V/pC, and the effective impedance was 3.59 mΩ(σ=10 mm).The simulation of the heat deposition on each part of the kicker demonstrated that 84.4%of the parasitic loss of the beam was deposited on the metal strips, and the total heat deposition power on the kicker was between 113.3 and 131.5 W. The obtained heat deposition powers can be considered as a reference for establishing the cooling system.

Microstructure and lateral conductivity control of hydrogenated nanocrystalline silicon oxide and its application in a-Si：H/a-SiGe：H tandem solar cells

Phosphorous-doped hydrogenated nanocrystalline silicon oxide （n-nc-SiOx：H） films are prepared via radio frequency plasma enhanced chemical vapor deposition （RF-PECVD）. Increasing deposition power during n-nc-SiOx：H film growth process can enhance the formation of nanocrystalline and obtain a uniform microstructure of n-nc-SiOx：H film. In addition, in 20s interval before increasing the deposition power, high density small grains are formed in amorphous SiOx matrix with higher crystalline volume fraction （Ic） and have a lower lateral conductivity. This uniform microstructure indicates that the higher Ic can leads to better vertical conductivity, lower refractive index, wider optical band-gap. It improves the back reflection in a-Si：H/a-SiGe：H tandem solar cells acting as an n-nc-SiOx：H back reflector prepared by the gradient power during deposition. Compared with the sample with SiOx back reflector, with a constant power used in deposition process, the sample with gradient power SiOx back reflector can enhance the total short-circuit current density （Jsc） and the initial efficiency of a-Si：H/a-SiGe：H tandem solar cells by 8.3% and 15.5%, respectively.

Two-Dimensional Self-Consistent Kinetic Model for Solenoidal Inductively Coupled Plasma

A two-dimensional self-consistent kinetic model was developed to study the influence of the various factors on the electron energy distribution function. These factors include gas pressure the driving frequency, the radius and length of the inductively coupled plasma equipment, the amplitude of the radio-frequency coil current, and the number of turns of rf coils. The spatial profiles of the rf electric field and power density have also been calculated under the same parameters. Numerical results show that the electron energy distribution functions are significantly modified and the spatial profiles of the rf electric field and rf power density are also demonstrated.

Optimization Study of ICRF Hydrogen Minority Heating in a Deuterium Plasma of EAST

The full wave TORIC code and the Kinetic Fokker-Planck SSFPQL code are com- bined to perform self-consistent simulations of the ICRF heating in the EAST 2D magnetic config- uration. The combined package is applied to the ICRF hydrogen minority heating in a deuterium plasma with the hydrogen concentration up to 10%. The fast wave propagation and absorption properties, power partitions among the plasma species and the RF driven energetic tails have been analyzed. Meanwhile, in order to optimize the ICRF heating, changing the resonance locations has also been considered in EAST plasmas.

A Ray-Tracing Analysis of ICRH in Tokamaks

Power deposition profiles generated by Ion Cyclotron Resonance Heating （ICRH） in non-circular tokamaks are studied using a ray-tracing technique. The simulation results for the Experimental Advanced Superconductor Tokamak （EAST） D-shaped plasma are presented. It is indicated that the spatial distributions of plasma parameters （plasma density, species temperature, minority ion concentration, etc.） have an significant influence on the power deposition profiles. The findings may be highly useful to the planned plasma heating and experiments in EAST.

Plasma–wave interaction in helicon plasmas near the lower hybrid frequency

We study the characteristics of plasma–wave interaction in helicon plasmas near the lower hybrid frequency.The(0D)dispersion relation is derived to analyze the properties of the wave propagation and a 1D cylindrical plasma–wave interaction model is established to investigate the power deposition and to implement the parametric analysis.It is concluded that the lower hybrid resonance is the main mechanism of the power deposition in helicon plasmas when the RF frequency is near the lower hybrid frequency and the power deposition mainly concentrates on a very thin layer near the boundary.Therefore,it causes that the plasma resistance has a large local peak near the lower hybrid frequency and the variation of the plasma density and the parallel wavenumber lead to the frequency shifting of the local peaks.It is found that the magnetic field is still proportional to the plasma density for the local maximum plasma resistance and the slope changes due to the transition.

Analysis of the Pipe Heat Loss of the Water Flow Calorimetry System in EAST Neutral Beam Injector

Neutral beam injection heating is one of the main auxiliary heating methods in controllable nuclear fusion research. In the EAST neutral beam injector, a water flow calorimetry （WFC） system is applied to measure the heat load on the electrode system of the ion source and the heat loading components of the beamline. Due to the heat loss in the return water pipe, there are some measuring errors for the current WFC system. In this paper, the errors were measured experimentally and analyzed theoretically, which lay a basis for the exact calculation of beam power deposition distribution and neutralization efficiency.

Study of the fast electron behavior in electron cyclotron current driven plasma on J-TEXT

In J-TEXT tokamak,fast electron bremsstrahlung diagnostic with 9 chords equipped with multichannel analyzer enables detailed studies of the generation and transport of fast electrons.The spatial profiles and energy spectrum of the fast electrons have been measured in two ECCD cases with either on-axis or off-axis injection,and the profiles processed by Abel-inversion are consistent with the calculated power deposition locations.Moreover,it is observed that the energy of fast electrons increases rapidly after turning off the ECCD,which may be attributed to the acceleration by the recovered loop voltage at low electron density.

The effect of discharge conditions of ICP etching reactor on plasma parameters

This study investigated the inductively coupled plasma etching reactor and RF coils developed by North Microelectronic Corporation. Full three dimensional simulations were made at different discharge conditions. The simulations examined and compared the distribution and non-uniformity of several plasma parameters at a fixed position upon the wafer at different pressures and coil currents. These parameters included electron density, electron temperature and power deposition. The results demonstrate that the electron density, power deposition and uniformity increase with either higher pressure or stronger coil currents, while the electron temperature decreases at this condition. Coil number increase can reduce the non-uniformity of parameters in the spatial distribution. The linear relationship between power deposition and electron density does not always exist. The comparison between simulation results and experiment results is also presented in the paper.

Progress of Project ＂Basic Characteristics of an A=2 Tokamak Reactor-like Plasma＂ during 2006

This report consists of two main research activities ： The first one is the study of MHD ballooning stability of tokamak plasmas, the second is about some fundamental aspect in the ECR wave propagation and power deposition. Main results are summarized here in three parts briefly. In the first part, the instabilities of tokamak plasma in the negative shear regime is studied and characteristics of the unstable mode is described, the scaling law of the growth rate over plasma parameters is given. In the second part, by using the restrict Solov＇ev configuration, the correctness of the usual s,α model in ballooning mode theory is analyzed. In the third part, the deposition of the power density of the ECR ordinary wave in the HL-2A plasma is calculated.

Theoretical Study of ECRH Heating Of HL-2A Tokamak Plasma

Electron cyclotron resonance heating （ECRH） is one of the main auxiliary heating schemes for the HL-2A tokamak. Routinely, the ohmic heating can provide a heating power about 300-450 kW in this device （ estimated from that the total toroidal current is about 300 kA while the totoidal voltage is 1-1.5 V）. The total power for the ECRH now is 1 MW and in future 2 MW.