Temperature diagnostics of ECR plasma by measurement of electron bremsstrahlung

The x-ray bremsstrahlung spectrum emitted by the electron population in a 14.5 GHz ECR plasma source has been measured using a NaI(Tl) detector, and hence the electron temperature of the higher energy electron population in the plasma has been determined. The x-ray spectra for Ne and Ar gases have been systematically studied as a function of inlet gas pressure from 7 × 10(-7) mbar to 7 × 10(-5) mbar and for input microwave power ～1 W to ～300 W. At the highest input power and optimum pressure conditions, the end point bremsstrahlung energies are seen to reach ～700 keV. The estimated electron temperatures (T(e)) were found to be in the range 20 keV-80 keV. The T(e) is found to be peaking at a pressure of 1 × 10(-5) mbar for both gases. The T(e) is seen to increase with increasing input power in the intermediate power region, i.e., between 100 and 200 W, but shows different behaviour for different gases in the low and high power regions. Both gases show very weak dependence of electron temperature on inlet gas pressure, but the trends in each gas are different.     

A tetrode based fast pulsed microwave source for electron cyclotron resonance breakdown experiments

To study electron cylotron resonance (ECR) breakdown and afterglow plasma in an experimental linear plasma system, a pulsed microwave source with rapid rise and fall of microwave power is desired. A pulsed microwave source with fast rise and fall capability for ECR breakdown experiments has been designed and tested for performance in the system. A tetrode, controlled by a modulator card, is used as a fast switch to initiate microwave power from a conventional magnetron operating at 2.45 GHz. The typical rise time of microwave power is approximately 3 micros and a fall time of approximately 10 micros. Using this scheme in a realistic pulsed microwave source at 800 W power, ECR breakdown of neutral gas is achieved and the plasma delay and fall time are observed from the plasma density measurements using a Langmuir probe. The design details of the fast rise pulsed microwave source are presented in this article with initial experimental results.     

Characterization of plasma parameters, first beam results, and status of electron cyclotron resonance source

Electron cyclotron resonance (ECR) plasma source at 50 keV, 30 mA proton current has been designed, fabricated, and assembled. Its plasma study has been done. Plasma chamber was excited with 350 W of microwave power at 2450 MHz, along with nitrogen and hydrogen gases. Microwave power was fed to the plasma chamber through waveguide. Plasma density and electron temperature were studied under various operating conditions, such as magnetic field, gas pressure, and transversal distance. Langmuir probe was used for plasma characterization using current-voltage variation. The nitrogen plasma density calculated was approximately 4.5 x 10(11) cm(-3), and electron temperatures of 3-10 eV (cold) and 45-85 eV (hot) were obtained. The total ion beam current of 2.5 mA was extracted, with two-electrode extraction geometry, at 15 keV beam energy. The optimization of the source is under progress to extract 30 mA proton beam current at 50 keV beam energy, using three-electrode extraction geometry. This source will be used as an injector to continuous wave radio frequency quadrupole, a part of 100 MeV proton linac. The required root-mean-square normalized beam emittance is less than 0.2pi mm mrad. This article presents the study of plasma parameters, first beam results, and status of ECR proton source.     

同步辐射光电离质谱检测氟原子在二氧化硅表面反应产物

采用微波放电等离子体源产生高密度F原子,结合同步辐射真空紫外光电离质谱全面检测F原子在二氧化硅表面刻蚀反应的产物,并探究其反应机理。通过扫描同步辐射光子能量,获得具有特定质量选择的离子光电离效率谱,测量了反应产物的电离能及碎片离子的出现势等基本参数;同时结合量子化学理论计算质谱中离子的来源,即对光电离和光解离过程进行了区分。结果表明,F原子在二氧化硅表面会反应生成一系列的氟氧硅化合物 (Si_xO_yF_z),主要包括SiF₄、SiF₃OSiF₃和SiFOSiF₂OF等,质谱中观察到的SiF₃⁺、SiF₃OSiF₂⁺等离子信号来源于其对应母体离子的解离碎片。实验测得SiF₄的电离能为15.85 eV,SiF₃⁺和SiF₃OSiF₂⁺碎片离子的出现势分别为16.20、16.40 eV。该方法实现了高效检测F原子刻蚀反应的产物,由于F原子具有较高的化学反应活性,该实验装置也可用于开展气相自由基反应研究,模拟大气化学和燃烧火焰等体系中的化学反应过程。     

Microwave ion source for high-current implanter

A long-life, high-current, microwave ion source for an electromagnetic mass separator is described. Ionization takes place due to the 2.45-GHz microwave discharge at a magnetic field intensity which is higher than the electron cyclotron resonance magnetic field. The discharge chamber is a ridged circular waveguide. The discharge region is restricted to a rectangular volume between the ridged electrodes by filling the remaining portions with dielectric. This source operates under low pressure (10(-2)-10(-3) Torr) and with high power efficiency. The incident microwave power is only several hundred watts at maximum output. When PH(3) gas is introduced, the total extracted current is about 40 mA with a 2x40-mm extraction slit. A P(+) ion implantation current of more than 10 mA is obtained by combining the source with a 40-cm radius, 60 degrees deflection magnetic mass separator.     

New design for a microwave discharge lamp

A simple discharge lamp with a microwave cavity fitting inside provides an intense source of VUV resonance radiation for photochemical work inside a vacuum chamber. Good coupling and minimum reabsorption result in better efficiency ( greater, similar1%) and more intense output power (up to 2.5x10(16) quanta s(-1)) than have been achieved previously.     

ECR sources of calcium plasma

The structure of the designed calcium plasma source for an installation for separating calcium isotopes based on the ion cyclotron resonance in plasma (ICR separation method) is described. Two variants of the source are presented: a source with a standalone calcium evaporator and a source with a solid calcium surface facing the discharge region. In both variants, an ECR discharge can be used to ionize calcium atoms (microwave discharge in a magnetic field at the electron cyclotron frequency).     

A high voltage pulsed power supply for capillary discharge waveguide applications

We present an all solid-state, high voltage pulsed power supply for inducing stable plasma formation (density ～10(18) cm(-3)) in gas-filled capillary discharge waveguides. The pulser (pulse duration of 1 μs) is based on transistor switching and wound transmission line transformer technology. For a capillary of length 40 mm and diameter 265 μm and gas backing pressure of 100 mbar, a fast voltage pulse risetime of 95 ns initiates breakdown at 13 kV along the capillary. A peak current of ～280 A indicates near complete ionization, and the r.m.s. temporal jitter in the current pulse is only 4 ns. Temporally stable plasma formation is crucial for deploying capillary waveguides as plasma channels in laser-plasma interaction experiments, such as the laser wakefield accelerator.     

Multigan®: first experimental results

A new design of a multicharged ion source based on the MONO1000 ECRIS has been presented at the last ECR ion source (ECRIS) Workshop 2010. [L. Maunoury et al., in Proceedings of the XIXth International Workshop on ECR Ion Sources, Grenoble, France, 23-26 August 2010] This source has not only two opening at both ends but also a large space in the middle of the source enabling a direct contact with the ECR plasma. The source has been assembled mechanically and put on a test bench at the Pantechnik company. The primary tests have shown that the plasma ignition occurred at low pressure (10(-6) mbar) and low RF power (10 W). The first experimental results ( = 1.30 for Ar and 1.85 for Xe) demonstrated the potential of this ion source in production of multicharged ion beams.     

Comparison between off-resonance and electron Bernstein waves heating regime in a microwave discharge ion source

A microwave discharge ion source (MDIS) operating at the Laboratori Nazionali del Sud of INFN, Catania has been used to compare the traditional electron cyclotron resonance (ECR) heating with an innovative mechanisms of plasma ignition based on the electrostatic Bernstein waves (EBW). EBW are obtained via the inner plasma electromagnetic-to-electrostatic wave conversion and they are absorbed by the plasma at cyclotron resonance harmonics. The heating of plasma by means of EBW at particular frequencies enabled us to reach densities much larger than the cutoff ones. Evidences of EBW generation and absorption together with X-ray emissions due to high energy electrons will be shown. A characterization of the discharge heating process in MDISs as a generalization of the ECR heating mechanism by means of ray tracing will be shown in order to highlight the fundamental physical differences between ECR and EBW heating.     

Low energy stable plasma calibration facility

We have designed and fabricated a low energy plasma calibration facility for testing and calibration of rocket-borne charged-particle detectors and for the investigation of plasma sheath formation in an environment with ionospheric plasma energies, densities, and Debye lengths. We describe the vacuum system and associated plasma source, which was modified from a Naval Research Laboratory design [Bowles et al. Rev. Sci. Instrum. 67, 455 (1996)]. Mechanical and electrical modifications to this cylindrical microwave resonant source are outlined together with a different method of operating the magnetron that achieves a stable discharge. This facility produces unmagnetized plasmas with densities from 1x10(3)/cm(3) to 6x10(5)/cm(3), electron temperatures from 0.1 to 1.7 eV, and plasma potentials from 0.5 to 8 V depending on varying input microwave power and neutral gas flow. For the range of input microwave power explored (350-600 W), the energy density of the plasma remains constant because of an inverse relationship between density and temperature. This relationship allows a wide range of Debye lengths (0.3-8.4 cm) to be investigated, which is ideal for simulating the ionospheric plasma sheaths we explore.     

Characterization of a linear device developed for research on advanced plasma imaging and dynamics

Within the scope of long term research on imaging diagnostics for steady-state plasmas and understanding of edge plasma physics through diagnostics with conventional spectroscopic methods, we have constructed a linear electron cyclotron resonance (ECR) plasma device named Research on Advanced Plasma Imaging and Dynamics (RAPID). It has a variety of axial magnetic field profiles provided by eight water-cooled magnetic coils and two dc power supplies. The positions of the magnetic coils are freely adjustable along the axial direction and the power supplies can be operated with many combinations of electrical wiring to the coils. Here, a 6 kW 2.45 GHz magnetron is used to produce steady-state hydrogen, helium, and argon plasmas with central magnetic fields of 875 and/or 437.5 G (second harmonic). In order to achieve the highest possible plasma performance within the limited input parameters, wall conditioning experiments were carried out. Chamber bake-out was achieved with heating coils that were wound covering the vessel, and long-pulse electron cyclotron heating discharge cleaning was also followed after 4 days of bake-out. A uniform bake-out temperature (150?°C) was achieved by wrapping the vessel in high temperature thermal insulation textile and by controlling the heating coil current using a digital control system. The partial pressure changes were observed using a residual gas analyzer, and a total system pressure of 5×10(-8)?Torr was finally reached. Diagnostic systems including a millimeter-wave interferometer, a high resolution survey spectrometer, a Langmuir probe, and an ultrasoft x-ray detector were used to provide the evidence that the plasma performance was improved as we desired. In this work, we present characterization of the RAPID device for various system conditions and configurations.     

微小等离子体反应器的制作及性能测试

设计了基于并行探针驱动的扫描刻蚀加工系统,用于微纳米尺度的刻蚀加工.研究了系统的核心器件—微小等离子体反应器的电学特性和发射光谱特性,以了解反应器中产生的反应等离子体性能的变化规律.基于微机电系统(MEMS)加工工艺制备了中间带有倒金字塔形状微型空腔的金属-绝缘体-金属3层结构的微小等离子体反应器.搭建了可测量等离子体伏安特性和发射光谱特性的实验系统,对放电气体为SF6,工作气压在5～12 kPa,直流驱动模式下的微小等离子体反应器的电学和光谱特性进行了测试.实验结果表明,放电电流随着放电电压的增加而近似线性递增,放电电流由5 kPa时的2.1～2.82 μA递增到12 kPa时的3.6～4.2 μA,表明所产生的微小等离子体处于异常辉光放电模态.当器件特征尺寸由150 μm减小至30 μm时,微小等离子体发射光谱中氟原子特征谱线(703.7 nm)峰值增大了约56％,表明微小等离子体的浓度随尺度缩小而增强.实验结果表明,设计的微小等离子体反应器基本满足扫描刻蚀加工所需的高浓度等离子体源的性能要求.     

Extraction of negative hydrogen ions from a compact 14 GHz microwave ion source

A pair of permanent magnets has formed enough intensity to realize electron cyclotron resonance condition for a 14 GHz microwave in a 2 cm diameter 9 cm long alumina discharge chamber. A three-electrode extraction system assembled in a magnetic shielding has formed a stable beam of negative hydrogen ions (H(-)) in a direction perpendicular to the magnetic field. The measured H(-) current density was about 1 mA∕cm(2) with only 50 W of discharge power, but the beam intensity had shown saturation against further increase in microwave power. The beam current decreased monotonically against increasing pressure.     

A microwave plasmatron

A waveguide-type plasmatron based on a waveguide-to-coaxial adapter (WCA) has been developed. Nitrogen is used as a plasma-forming medium. The microwave discharge initiator based on a disordered stacking of tungsten spirals placed on the end wall of the inner conductor of the coaxial line of WCA has been designed and experimentally tested. A sustained plasma torch is obtained at the atmospheric pressure and a microwave generator power of 1.5 kW. The designed plasmatron is oriented to application in plants for utilizing associated petroleum gas and producing a methane-hydrogen mixture and a carbon nanomaterial.     

Cold plasma brush generated at atmospheric pressure

A cold plasma brush is generated at atmospheric pressure with low power consumption in the level of several watts (as low as 4 W) up to tens of watts (up to 45 W). The plasma can be ignited and sustained in both continuous and pulsed modes with different plasma gases such as argon or helium, but argon was selected as a primary gas for use in this work. The brush-shaped plasma is formed and extended outside of the discharge chamber with typical dimension of 10-15 mm in width and less than 1.0 mm in thickness, which are adjustable by changing the discharge chamber design and operating conditions. The brush-shaped plasma provides some unique features and distinct nonequilibrium plasma characteristics. Temperature measurements using a thermocouple thermometer showed that the gas phase temperatures of the plasma brush are close to room temperature (as low as 42 degrees C) when running with a relatively high gas flow rate of about 3500 ml/min. For an argon plasma brush, the operating voltage from less than 500 V to about 2500 V was tested, with an argon gas flow rate varied from less than 1000 to 3500 ml/min. The cold plasma brush can most efficiently use the discharge power as well as the plasma gas for material and surface treatment. The very low power consumption of such an atmospheric argon plasma brush provides many unique advantages in practical applications including battery-powered operation and use in large-scale applications. Several polymer film samples were tested for surface treatment with the newly developed device, and successful changes of the wettability property from hydrophobic to hydrophilic were achieved within a few seconds.     

Subcutoff microwave driven plasma ion sources for multielemental focused ion beam systems

A compact microwave driven plasma ion source for focused ion beam applications has been developed. Several gas species have been experimented including argon, krypton, and hydrogen. The plasma, confined by a minimum B multicusp magnetic field, has good radial and axial uniformity. The octupole multicusp configuration shows a superior performance in terms of plasma density (~1.3 x 10(11) cm(-3)) and electron temperature (7-15 eV) at a power density of 5-10 Wcm(2). Ion current densities ranging from a few hundreds to over 1000 mA/cm(2) have been obtained with different plasma electrode apertures. The ion source will be combined with electrostatic Einzel lenses and should be capable of producing multielemental focused ion beams for nanostructuring and implantations. The initial simulation results for the focused beams have been presented.     

Microsecond time-resolved Fourier transform infrared analytics in a low pressure glow discharge reactor

A low pressure glow discharge reactor has been designed to allow time-resolved infrared spectroscopic investigation of the discharge zone in practical conditions. The benefits of such reactor are demonstrated through the study of the evolution in the infrared spectra of air/CO(2) gas mixture at the microsecond time-scale. It has been shown that the spectra are greatly affected by the electrical discharge in the 2400-2200?cm(-1) region, where the asymmetric stretch mode of CO(2) falls. The CO(2) molecules are excited through a collision with excited N(2) molecules, where the transfer of energy occurs by a resonant effect. The mechanisms involved are reversible and following plasma pulses.     

N2分子二聚物在352.3 nm处增益特性研究

利用微波放电激励高纯氮,并采用放大自发辐射法,研究了不同微波激励功率和不同N₂气压条件下N₂分子二聚物352.3nm辐射的增益特性。给出了沿放电管轴线N₂分子二聚物352.3nm辐射的小信号增益系数随微波激励功率和充入放电管N₂气压变化的规律。研究结果表明当微波功率大于100W时,充入N₂气压在330~1 800Pa范围内,N₂分子二聚物在352.3nm处存在受激辐射特性。当微波功率为500W,充入放电管的N₂气压为1 100Pa时,N₂分子二聚物352.3nm辐射的小信号增益系数最大为1.08%cm^-1。另外,还给出了N₂分子二聚物352.3nm辐射增益沿放电管径向分布情况。 N₂分子二聚物352.3nm辐射的增益系数在放电管中心最小,接近管壁时最大。     

A pulse-periodic gyroresonant plasma accelerator

A plasma electron accelerator based on the gyromagnetic autoresonance effect is described. Electrons of the initially cold internal-injection plasma (a classical ECR discharge) are accelerated in the magnetic field of a magnetic mirror trap under a one-stage effect of the resonant microwave field and an additional pulsed magnetic field. The synchronism in maintaining the resonance conditions is ensured by a smooth increase in the pulsed magnetic field in the course of a microwave pulse. At the moderate values of the input microwave power (up to 2.5 kW) and the steady-state and pulsed magnetic fields (each up to 1 kG), it is possible to obtain stable relativistic plasma bunches, in which the energy of the electron components is a few hundred keV. The measured X-ray bremsstrahlung spectra have features characteristic of the energy distribution of photons, and the high-energy tails are recorded in the region of 600–800 keV. The dependences of the bremsstrahlung characteristics on the experimental conditions—the value of the steady-state magnetic field and the amplitude of the pulsed magnetic field—are investigated. The experimental data are in good agreement in the quantitative sense with the results of the computer simulation and with the earlier studies.