Investigation and application of hollow anode glow discharge ion source

In the present work, a new shape of a glow discharge ion source has been designed, fabricated and constructed at Accelerators and Ion Sources Department, Nuclear Research Center, Egyptian Atomic Energy Authority, Egypt. The discharge and output beam characteristics of the ion source at different operating gas pressures have been measured at the optimum distance between the anode and the cathode (3.5 mm) using hydrogen and nitrogen gases. Furthermore, mixture of different gases was studied, e.g., addition of H₂ gas to N₂ gas with different ratios has been investigated. Finally, as an application of this new ion source, ion beam modification of insulators (glass) which depends on glass structure has been achieved. It has been found that, the transmission of light is decreased by coating the glass surface with Ar ion beam more than coating with plasma of Ar gas at the same pressure and the same exposure time. So we could use this ion source as a coating tool for borate glass surface. The parameters affected the glow discharge ion source efficiency have been examined carefully using a mixture of gases. Using helium gas, the glow discharge is in a turbulent state due to instabilities. An investigated H₂-N₂ mixture has been used in order to obtain an optimum percentage of the mixture of the two gases to increase the electric field necessary for ionization balance.     

A direct current glow discharge plasma source for inner surface modification of metallic tube

A dc glow discharge plasma source was developed for inner surface modification of metallic tubes with an inner diameter of 10 mm. A tungsten wire of 30 μm thick was stretched inside the tube to form coaxial electrodes. DC glow discharge plasma was generated inside the tube by applying a negative high dc voltage to the tube. It was found that the length of the cylindrical plasma bulk depends linearly on the applied voltage. The electron excitation temperature of Ar plasma was measured as 12830 ± 550 K by optical emission spectroscopy method. As a preliminary application, diamond-like carbon (DLC) films were deposited onto the inner surface of stainless steel tube of 100 mm in length and 10 mm in inner diameter by using CH₄/Ar mixture with 40% CH₄ at 40 Pa pressure. The chemical structure of the DLC film deposited on the substrate was analyzed by Raman spectroscopy. The integrated intensity ratio (I_D:I_G) was obtained as 1.62 from the Raman spectra. The thickness of the DLC film deposited on the substrate was estimated as 1.5 μm by scanning electron microscopy (SEM) observation.     

Study on the ablation modification effects for EB-PVD ceramic coatings considering the microstructure of the surface

Based on the surface microstructure of EB-PVD ZrO₂ coatings, the ablation effects of a novel method for ceramic modification technique by high-intensity pulsed ion beam irradiation have been studied numerically. Taking the nonlinear depositing energy of ions in the coatings calculated by Monte Carlo methods as the thermal source term in heat transfer equations, the surface melting process and the evolution of temperature of ZrO₂ specimens induced by HIPIB irradiation were obtained. About 1 μm in thickness of ZrO₂ ceramic was re-solidified after melting, a dense modification coat layer formed, and near the top surface an even denser layer formed. During the calculation the latent heat of ZrO₂ is introduced to consider the additional heat due to the phase change between solid-liquid and liquid-gas states. The numerical result about the ablation melted thickness of surface layer is in reasonable agreement with those measured by HIPIB irradiation experiments.     

Design and Development of a Power Supply System for NBI Test Stand of EAST

A neutral beam injector (NBI) test stand was constructed to develop a multi-megawatt prototype ion source as an auxiliary heating system on experimental advanced superconducting tokamak. A power supply system for the NBI test stand components such as a set of dc power supplies for plasma generator, a dc high voltage power supply of a tetrode accelerator, a transmission line and a surge energy suppressor. Stable arc discharges of the plasma generator with hydrogen gases for 100 s long pulse have been produced by six Langmuir probes feedback loop regulation mode to control the arc power supply. The 4 MW hydrogen ion beam of 1 s is extracted with beam energy of 80 keV and the beam current of 52 A. The dc high voltage power supply for the plasma grid of the prototype ion source was designed to contribute maximum voltage of 100 kV and current of 100 A. The high voltage power output is continuously adjustable to satisfy with plasma physics experiment in operation frequency of 10 Hz. To prevent damage of the beam source at high voltage breakdown, core snubber using deltamax soft magnetic materials have been adopted to satisfy the input energy into the accelerator from the power supply can be reduced to about 5 J in the case of breakdown at 80 kV. For the transmission line, a disc shape multi cable coaxial configuration was adopted and which the dimension of the diameter is 140 mm at the core snubber. The major issues of discharge characteristics with long pulse and beam extraction with high power for the prototype ion source were investigated on the NBI test stand.     

低能高束流氩离子源的结构及性能

离子源技术是等离子体研究中的一项重要内容,而低能大束流源则是离子源技术研究中的一个重要方向,因为这样的源在离子束刻蚀、离子束溅射镀膜以及荷能粒子与物质相互作用方面都有广泛的应用;本文采用空心阴极空心阳极结构,用热阴极电子发射弧放电驱动并用磁场约束产生等离子体,用曲面发射引出离子束,研制成了氩气放电溅射离子源;研究了灯丝加热电流、弧压对弧流的影响和弧流与工作气体压力对离子束引出的影响规律.离子源的引出电压在0-4.0 kV之间连续可调,最大引出束流为100 mA,束斑面积为φ6.0 cm,以Ti为溅射靶时的最大溅射沉积率为0.45 nm/s,离子源可连续工作160 h.     

A scoping study of the application of neutral beam heating on the TCV tokamak

The TCV tokamak contributes to the physics understanding of fusion plasmas, broadening the parameter range of reactor relevant regimes, by investigations based on an extensive use of the existing main experimental tools: flexible shaping and high power real time-controllable electron cyclotron heating (ECH) and current drive (ECCD) systems. A proposed implementation of direct ion heating on the TCV by the installation of a 20–35 keV neutral beam injection (NBI) with a total power of 1–3 MW would permit an extension of the accessible range of ion to electron temperatures (T_i/T_e ～ 0.1–0.8) to well beyond unity, depending on the NBI/ECH mix and the plasma density. A NBI system would provide TCV with a tool for plasma study at reactor relevant T_i/T_e ratios ～1 and in investigating fast ion and MHD physics together with the effects of plasma rotation and high plasma β scenarios. The feasibility studies for a NBI heating on TCV presented in this paper were undertaken to construct a specification for the neutral beam injectors together with an experimental geometry for possible operational scenarios.     

Low Pressure Hexamethyldisiloxane (HMDSO)/Nitrogen Plasma Treatment on the Wettability and Surface Free Energy of Biaxial-Oriented Polypropylene (BOPP) Films

In this paper the influence of DC glow discharge HMDSO-N₂ plasma on wettability and surface properties of Biaxial-oriented polypropylene (BOPP) polymeric surfaces, has been investigated. The effects of plasma exposure time and HMDSO percent on the surface energy and wettability of the BOPP films were characterized using Fourier transform infrared spectroscopy (FTIR), Atomic force microscopy (AFM) and contact angle measurement. A clear change in the surface energy of BOPP films due to plasma treatment was observed. In this work we report changing surface properties of BOPP films instead of plasma treatment time and HMDSO ratios.     

高压脉冲辉光放电内表面注入及等离子体特征研究

为了提高内表面注入的剂量及深度均匀性,作者将脉冲高压辉光放电机制引入到内表面改性的研究中.利用发射光谱法及静电探针法对该方法获得的离子体参数进行了诊断,并在特定的内筒中采用氮气为工作气,进行了离子注入实验.结果显示,采用这种方法可以在内筒获得连续存在的等离子体.Ar等离子中含有大量激发态原子,而N等离子体中N2+离子占离子数量的绝大多数.等离子密度随着电压的提高显著提高,当电压从10kV增加到15kV时,Ar等离子体中离子密度增加约4倍,N等离子中离子密度增加约2倍.内表面获得均匀性良好的改性层,对于直径56mm的圆筒在电压20kV、气压1.5Pa条件下注入深度达到16.9nm,剂量均匀性可达到87.3%.     

Simulation of Radial Electric Field and Internal Transport Barrier Formation in Small Size Divertor Tokamak Plasma Edge

The simulation of the radial electric field shear, which is responsible for L-H transition by means B2SOLPS0.5.2D transport code, gives the dependence of this shear on plasma parameters. Also, as result of uni-directional neutral beam heating, internal transport barrier is formed and ion radial heat flux q _ir starts to decrease. Furthermore, the dependence of radial electric field shear on ion temperature gradient ITG has also investigated.     

Flow Dynamics and Plasma Heating of Spheromaks in SSX

We report several new experimental results related to flow dynamics and heating from single dipole-trapped spheromaks and spheromak merging studies at SSX. Single spheromaks (stabilized with a pair of external coils, see Brown, Phys. Plasmas 13 102503 (2006)) and merged FRC-like configurations (see Brown, Phys. Plasmas 13, 056503 (2006)) are trapped in our prolate (R = 0.2 m, L = 0.6 m) copper flux conserver. Local spheromak flow is studied with two Mach probes (r ₁ ≤ ρ _i , r ₂ ≥ ρ _i ) calibrated by time-of-flight with a fast set of magnetic probes at the edge of the device. Both Mach probes feature six ion collectors housed in a boron nitride sheath. The larger Mach probe will ultimately be used in the MST reversed field pinch. Line averaged flow is measured by ion Doppler spectroscopy (IDS) at the midplane. The SSX IDS instrument measures with 1 μs or better time resolution the width and Doppler shift of the C _III impurity (H plasma) 229.7 nm line to determine the temperature and line-averaged flow velocity (see Cothran, RSI 77, 063504 (2006)). We find axial flows up to 100 km/s during formation of the dipole trapped spheromak. Flow returns at the wall to form a large vortex. Recent high-resolution IDS velocity measurements during spheromak merging show bi-directional outflow jets at ±40 km/s (nearly the Alfvén speed). We also measure T _i ≥ 80 eV and T _e ≥ 20 eV during spheromak merging events after all plasma facing surfaces are cleaned with helium glow discharge conditioning. Transient electron heating is inferred from bursts on a four-channel soft x-ray array. The spheromaks are also characterized by a suite of magnetic probe arrays for magnetic structure B(r,t), and interferometry for n _e . Finally, we are designing a new oblate, trapezoidal flux conserver for FRC studies. Equilibrium and dynamical simulations suggest that a tilt-stable, oblate FRC can be formed by spheromak merging in the new flux conserver.     

In-depth analysis of ITER-like samples composition using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopic in-depth measurements were undertaken for two ITER-like calibrated multi-layered samples made of W-Mo or W/C layers on Ti-substrates. The samples were previously characterized by glow discharge optical emission spectroscopy. For laser-induced breakdown spectroscopic measurements, pulses generated by Nd:YAG laser sources with 1064 nm, 532 nm, 355 nm and 266 nm wavelengths were applied. The effects of laser beam shaping, fluence and wavelength as well as the gas nature (air, Ar, He) and pressure were investigated. The results obtained with laser-induced breakdown spectroscopic in-depth measurements were compared to those obtained with glow discharge optical emission spectroscopy and found to be in agreement. However, a mixing of the layers was observed and attributed to diffusion through the melted material and to the non-homogeneity of the laser beam spatial distribution. The depth resolution was found of the order of several thermal diffusion lengths but should be improved by using picosecond laser pulse duration.The results promote applications to tritium concentration measurements with depth resolution in the deposited layers of Tokamak first walls, as in the case of the future fusion reactor ITER.     

A study of low-energy ion induced radiolysis of thiol-containing amino acid cysteine in the solid and aqueous solution states

The radiolysis of cysteine under plasma discharge and irradiation of low-energy ion beam was investigated. The damage of cysteine in aqueous solution under discharge was assessed via the acid ninhydrin reagent and the yield of cystine produced from the reaction was analyzed by FTIR. In addition, the generation of hydrogen sulfide was also identified. The destruction of solid cysteine under low-energy ion beam irradiation was estimated via monitoring IR bands of different functional groups (–SH, –NH₃, –COO^?) of cysteine, and the production of cystine from ion-irradiated solid cysteine after dissolution in water was also verified. These results may help us to understand the inactivation of sulphydryl enzymes under direct and indirect interaction with the low-energy ion irradiation.     

Simulation of the Radial Electric Field Shear in the Edge Plasma of Small Size Divertor Tokamak

The simulation of the radial electric field shear, which is responsible for L-H transition by means B2SOLPS0.5.2D transport code, gives the dependence of this shear on plasma parameters. Also, as result of uni-directional neutral beam heating, internal transport barrier is formed and ion radial heat flux q _ir starts to decrease. Furthermore, the dependence of radial electric field shear on ion temperature gradient ITG has also investigated.     

Irradiation Test of Stainless Steel by High Power CO2 Laser

Electron beam, plasma arc and ion beam are often employed to simulate the high heat flux applied to the first wall or the divertor plate in a fusion reactor. In this study, an irradiation test with high heat flux was carried out under atmospheric condition by using high power CO₂ laser. The test material is SUS316 and the temperature change and the melting amount were measured. A thermal analysis code to take melting and evaporation behavior into account was developed. The laser absorption coefficient can be raised up to 95% before melting if special paint is coated on specimen surface. After melting, this coefficient is estimated to be 60% by thermal analysis. However, it was revealed that a precise modification of this model was indispensable. Although the effect of irradiation environment or heat source on material damage was also examined, there is no significant difference one another. In conclusion, it is found that CO₂ laser is quite suitable for use as a heat source to simulate a high heat flux.     

Control of Beam Energy and Flux Ratio in an Ion-Beam-Background Plasma System Produced in a Double Plasma Device

Plasmas containing ion beams have various applications both in plasma technology and in fundamental research. The ion beam energy and flux are the two factors characterizing the beam properties. Previous studies have not achieved the independent adjustment of these two parameters. In this paper, an ion-beam-background-plasma system was produced with hotcathode discharge in a double plasma device separated by two adjacent grids, with which the beam energy and flux ratio(the ratio between the beam flux and total ion flux) can be controlled independently. It is shown that the discharge voltage(i.e., voltage across the hot-cathode and anode) and the voltage drop between the two separation grids can be used to effectively control the beam energy while the flux ratio is not affected by these voltages. The flux ratio depends sensitively on hot-filaments heating current whose influence on the beam energy is relatively weak,and thus enabling approximate control of the flux ratio     

Development and testing of 140 GHz absorber coatings for the water baffle of W7-X cryopumps

Due to the relatively high strayfield radiation (140 GHz) from the electron cyclotron radio frequency heating system to which the W7-X cryopumps are expected to be subjected, coating systems acting as an efficient absorber for 140 GHz radiation have been developed for the water-cooled baffle shield in order to reduce the thermal load on the liquid N shield and the liquid He cryopanel.Several types of oxide ceramic coatings were applied on planar copper substrates by Atmospheric Plasma Spraying. The influence of the process parameters on the coating properties and microwave absorbing capability was analysed. It was found that film thickness and microstructure of the sprayed coatings have a significant influence on microwave absorption behaviour. For Al₂O₃/TiO₂ coatings, absorption values over 90% were obtained for the 140 GHz probing beam.After optimisation of the coating structure for maximum microwave absorption, the coating procedure was adapted by special robot trajectories to the complex water baffle geometry. The selected spray parameters and kinematics were then used for the complete coating of four mock-ups, which have been tested in the W7-X strayfield test facility Mistral. The mock-ups showed absorption values of 75%.     

Radiation damage (blistering) in Al,Cu, Si by exposure to a plasma focus discharge

Plates of Al, Cu (polycrystalline) and Si (monocrystal) have been irradiated with beams of D⁺ ions (keV to MeV) and other radiation by exposure to a single discharge of a 5–10-kJ Plasma Focus in deuterium. Scanning electron microscope and elemental X-ray energy dispersive analysis are used for diagnostics. The nonuniformity of the ion beam causes a nonuniform damage with formation of clusters of blisters. A statistical analysis of blister parameters (diameter and skin thickness) is used to investigate the internal structure of a deuteron beam ejected from the plasma. The value K ～ 10–20 keV is obtained as the typical ion energy for the bulk of the deuterons and an ion energy E ～ 200–230 keV is typical for individual ion groups (ion strings) forming the high-energy deuteron beam.     

Effect of Low Pressure Nitrogen DC Plasma on Optical Properties of Biaxial-Oriented Polypropylene (BOPP), Poly Methyl Methacrylate (PMMA) and Poly Vinyl Chloride (PVC) Films

In this paper properties of Biaxial-Oriented Polypropylene, Poly Vinyl Chloride and Poly Methyl Methacrylate samples treated by DC glow discharge of N₂ plasma have been investigated by UV–Vis_NIR spectrophotometer. It was found that plasma treatment change chemical structure of polymer surfaces. In addition, absorption coefficient, refractive index and extinction coefficient of all treated samples have been slightly changed.     

Formation of Electron Internal Transport Barrier in Edge Plasma of Small Size Divertor Tokamak

The formation of electron internal transport barrier (EITB) during using counter-neutral beam injection (NBI) heating in the edge plasma of small size divertor tokamak can be simulated by using fluid transport code B2SOLPS0.5.2D. The results of simulations give us the following: (1) Plasma heating with counter-neutral beam injection leads to, strong, parabola type electron internal transport barrier (EITB) was formed in the edge plasma of small size divertor tokamak. (2) In case of plasma heating by counter-neutral beam injection, the radial electric field shear (E _r –gradient) was increased, while electron transport coefficients were reduced in conjunction with the formation of electron internal transport barrier (EITB). (3) The plasma heating by counter-neutral beam injection play significantly role in redistribution of parallel (toroidal) velocity in edge plasma of small size divertor tokamak.