Gas discharge source of metal vapor and fast gas atoms

A source of metal atom flow coinciding in time and space with a flow of fast gas atoms has been studied and the study results are presented. The fast particles are produced due to charge exchange collisions of ions accelerated by potential difference between a plasma emitter inside the source and secondary plasma inside a process vacuum chamber. The emitter is the glow discharge plasma, whose electrons are confined in an electrostatic trap formed by a cold hollow cathode and an emissive grid the latter being negative both to the cathode and the chamber. The metal atoms are produced due to sputtering a target placed at the hollow cathode bottom by ions from the plasma emitter with energy up to 3 keV. Sputtered atoms cross the emitter, together with accelerated ions enter the chamber through the emissive grid and deposit on pieces placed therein. When a mixture of argon and nitrogen is used, the metal nitride coatings are being synthesized and interruptedly bombarded during the synthesis by atoms and molecules with energy variable from ～10 to ～300 eV.     

Low-energy linear oxygen plasma source

A new version of a constricted plasma source is described, characterized by all metal-ceramic construction, a linear slit exit of 180 mm length, and cw operation (typically 50 kHz) at an average power of 1.5 kW. The plasma source is here operated with oxygen gas, producing streaming plasma that contains mainly positive molecular and atomic ions, and to a much lesser degree, negative ions. The maximum total ion current obtained was about 0.5 A. The fraction of atomic ions reached more than 10% of all ions when the flow rate was less then 10 SCCM O(2), corresponding to a chamber pressure of about 0.5 Pa for the selected pumping speed. The energy distribution functions of the different ion species were measured with a combined mass spectrometer and energy analyzer. The time-averaged distribution functions were broad and ranged from about 30 to 90 eV at 200 kHz and higher frequencies, while they were only several eV broad at 50 kHz and lower frequencies, with the maximum located at about 40 eV for the grounded anode case. This maximum was shifted down to about 7 eV when the anode was floating, indicating the important role of the plasma potential for the ion energy for a given substrate potential. The source could be scaled to greater length and may be useful for functionalization of surfaces and plasma-assisted deposition of compound films.     

电感耦合等离子体离子源分析性能的影响因素探究

ICP(电感耦合等离子体)离子源是目前质谱分析中最常用的离子源之一,具有电离效率高、分析产物主要为单电荷离子等特点。因其优良的性能,现已广泛应用于不同行业中。为了继续提升ICP-MS(电感耦合等离子体质谱)的分析性能,拓宽应用领域,许多学者通过实验研究,建模仿真对ICP离子源进行了深入研究。本文对这些工作进行了阐述,介绍了不同的影响因素对等离子体特性的影响。如气体流速、功率大小、采样深度等,并对有无质谱采样接口时的等离子体的特性进行比较,为优化等离子体离子源提供思路。     

A subnanosecond pulsed ion source for micrometer focused ion beams

A new, compact design of an ion source delivers nanosecond pulsed ion beams with low emittance, which can be focused to micrometer size. By using a high-power, 25 fs laser pulse focused into a gas region of 10(-6) mbar, ions at very low temperatures are produced in the small laser focal volume of 5 mum diameter by 20 mum length through multiphoton ionization. These ions are created in a cold environment, not in a hot plasma, and, since the ionization process itself does not significantly heat them, have as a result essentially room temperature. The generated ion pulse, up to several thousand ions per pulse, is extracted from the source volume with ion optical elements that have been carefully designed by simulation calculations. Externally triggered, its subnanosecond duration and even smaller time jitter allow it to be superimposed with other pulsed particle or laser beams. It therefore can be combined with any type of collision experiment where the size and the time structure of the projectile beam crucially affect the achievable experimental resolution.     

Ion beam capture and charge breeding in electron cyclotron resonance ion source plasmas

Beam capture of injected ions and charge breeding in electron cyclotron resonance (ECR) charge breeder ion source plasmas has been investigated utilizing an ECR plasma modeling code, the generalized ECR ion source model, and a Monte Carlo beam capture code. Beam capturing dynamics, charge breeding in the plasma, and the extracted charged ion states are described. Optimization of ion beam energy is performed for (1) high beam capture efficiency and (2) high charge state ion beam extractions. A sample case study for ANL-ECR has been performed. Ions entering ECR ion source plasma are slowed down mostly by the background ions. Assuming Maxwellian plasma ions, maximum beam energy loss occurs when the beam velocity is around the background thermal velocity in magnitude. It is also found that beam capture location affects charge state distribution. For instance, with a majority of beam ions captured near the middle of the device higher currents for higher charge states are obtained. The beam ions captured near the entry have a higher probability of backstreaming after they are captured. For this reason, the optimum beam energy of the injected Ar(+) beam ions for charge breeding is generally higher than the optimum input beam energy for maximum beam energy loss.     

High-energy metal ion implantation for reduction of surface resistivity of alumina ceramic

In this work, the possibility to increase the surface conductivity of ceramic insulators through their treatment with accelerated metal ion beams produced by a MevvaV.Ru vacuum arc source is demonstrated. The increase in surface conductivity is made possible due to experimental conditions in which an insulated collector is charged by beam ions to a potential many times lower than the accelerating voltage, and hence, than the average beam ion energy. The observed effect of charge neutralization of the accelerated ion beam is presumably associated with electrons knocked out of the electrodes of the accelerating system of the source and of the walls of the vacuum chamber by the accelerated ions.     

高能量离子束诊断质谱仪的研制及性能表征

本研究开发了一台应用于高能量离子束诊断的直线式飞行时间质谱仪,实现了其与高能真空弧放电离子源的联用。该仪器加速电压30 kV,飞行腔有效飞行距离1.5 m,通过短脉冲离子门精确截取,ICCD高速相机优化聚焦,仪器分辨率优于90 FWHM,对放电过程中产生的等离子体可实现不同时间的离子成分分析。将该方法用于真空弧放电离子源放电过程中离子成分的检测,放电2 μs时,电离成分以气态离子C⁺、O⁺、C²⁺、O²⁺为主;放电6 μs后,除气体成分外,还可以检测到Fe⁺、Cu⁺及其同位素金属离子峰。该仪器能够给出离子源放电产生离子的种类、价态以及相对含量等信息,可实现整个放电过程产生离子成分信息的准确诊断。     

Sheath structure in negative ion sources for fusion (invited)

In fusion negative ion sources, the negative ions are formed on the caesiated plasma grid predominantly by hydrogen atoms from the plasma. The space charge of the negative ions leaving the wall is not fully compensated by incoming positive ions and at high enough emission a virtual cathode is formed. This virtual cathode limits the flux of negative ions transported across the sheath to the plasma. A 1D collisionless model of the sheath is presented taking into account the virtual cathode. The model will be applied to examples of the ion source operation. Extension of the model to the bulk plasma shows good agreement with experimental data. A possible role for fast ions is discussed.     

A method for monitoring the parameters of a stripping target in neutral particle analyzers for the ITER

A method is described, which will be used as a basis for designing a system for monitoring the parameters of a stripping target in neutral particle analyzers being developed for neutral particle diagnostics of the ITER plasma. This method is based on examining the target by a beam of alkali ions and measuring the energy spectrum of the beam passed through it. Results of testing of this method at the experimental facility—a model of the monitoring system—are presented. Based on analysis of the experimental data obtained in the study, conclusions are drawn on the applicability of this method to monitoring of the stripping target parameters.     

气体流量与射频功率对电感耦合等离子体温度分布的影响

针对以电感耦合等离子体（ICP）为激发光源的分析仪器，研究ICP的温度空间分布对样品电离和激发具有重要意义。本研究建立了ICP的二维轴对称模型，利用有限元方法解算磁流体力学方程组，得到ICP的最高温度和温度空间分布，并研究了气体（辅助气、冷却气）流量和射频功率对ICP的最高温度和温度空间分布的影响。结果表明，辅助气、冷却气的流量及射频功率几乎不会改变ICP的最高温度（约10 000 K），但会改变ICP的温度空间分布；辅助气流量的增大有助于ICP中心通道的形成，样品通过中心通道，有利于样品的原子化和电离；对于矩管直径为20 mm的ICP，未通入样品时，运行时的射频功率在理论上不能超过1 600 W，而实际上空载功率可能更低。     

A High-Current Pulse Generator SIGNAL with an Inductive Energy Storage and a Microsecond Plasma Opening Switch

The primary energy storage in the SIGNAL installation is a 4.7-F capacitor bank with a stored energy of up to 24 kJ switched by a gas-discharge gap switch of the trigatron type. The plasma source and the design of the microsecond plasma opening switch ensure current flow through this switch and inductive storage for a time of up to 1.7 s. The current amplitude reaches 330 kA. The current switched to the load is 20–300 kA in various modes with a rise time of 10–200 ns. The voltage across the feedthrough insulator reaches 400 kV. The installation is used in experimental studies of linear pinches, capillary discharge, and microsecond plasma opening switches.     

Analysis and modelling of edm parameters

Metal removal in electro-discharge machining (edm) is basically a thermal erosion process where the heat transfer is predominantly through conduction. In this paper, a two-dimensional heat transfer model, assuming the plasma channel to be a disc heat source, has been employed to study the effects of edm input parameters, such as pulse duration, pulse energy and material properties, on metal removal and crater shape. Reasons for somewhat poor correlation between theoretical and experimental data are discussed.     

Design of a cavity ring-down spectroscopy diagnostic for negative ion rf source SPIDER

The rf source test facility SPIDER will test and optimize the source of the 1 MV neutral beam injection systems for ITER. Cavity ring-down spectroscopy (CRDS) will measure the absolute line-of-sight integrated density of negative (H(-) and D(-)) ions, produced in the extraction region of the source. CRDS takes advantage of the photodetachment process: negative ions are converted to neutral hydrogen atoms by electron stripping through absorption of a photon from a laser. The design of this diagnostic is presented with the corresponding simulation of the expected performance. A prototype operated without plasma has provided CRDS reference signals, design validation, and results concerning the signal-to-noise ratio.     

Electrostatic energy analyzer measurements of low energy zirconium beam parameters in a plasma sputter-type negative ion source

A plasma sputter-type negative ion source is utilized to produce and detect negative Zr ions with energies between 150 and 450 eV via a retarding potential-type electrostatic energy analyzer. Traditional and modified semi-cylindrical Faraday cups (FC) inside the analyzer are employed to sample negative Zr ions and measure corresponding ion currents. The traditional FC registered indistinct ion current readings which are attributed to backscattering of ions and secondary electron emissions. The modified Faraday cup with biased repeller guard ring, cut out these signal distortions leaving only ringings as issues which are theoretically compensated by fitting a sigmoidal function into the data. The mean energy and energy spread are calculated using the ion current versus retarding potential data while the beam width values are determined from the data of the transverse measurement of ion current. The most energetic negative Zr ions yield tighter energy spread at 4.11 eV compared to the least energetic negative Zr ions at 4.79 eV. The smallest calculated beam width is 1.04 cm for the negative Zr ions with the highest mean energy indicating a more focused beam in contrast to the less energetic negative Zr ions due to space charge forces.     

Fast ion beam-plasma interaction system

A device has been constructed for the study of the interaction between a fast ion beam and a target plasma of separately controllable parameters. The beam of either hydrogen or helium ions has an energy of 1-4 keV and a total current of 0.5-2 A. The beam energy and beam current can be varied separately. The ion source plasma is created by a pulsed (0.2-10-ms pulse length) discharge in neutral gas at up to 3 x 10(-3) Torr. The neutrals are pulsed into the source chamber, allowing the neutral pressure in the target region to remain less than 5 x 10(-5) Torr at a 2-Hz repetition rate. The creation of the source plasma can be described by a simple set of equations which predict optimum source design parameters. The target plasma is also produced by a pulsed discharge. Between the target and source chambers the beam is neutralized by electrons drawn from a set of hot filaments. Currently under study is an unstable wave in a field-free plasma excited when the beam velocity is nearly equal to the target electron thermal velocity (v(beam) approximately 3.5 x 10(7) cm/s, Te = 0.5 eV).     

XUV laser-plasma source based on solid Ar filament

We present a laser driven soft x-ray source based on a novel solid argon filament. The continuously flowing micron-sized filament (diameter approximately 56 microm, flow speed approximately 5 mms) was used as a laser target in order to generate a plasma source of high brightness in the "water window" (2.2-4.4 nm) spectral range. The emission properties of the source were characterized in detail with respect to crucial parameters such as positional and energy stability using an extreme ultraviolet (XUV) sensitive pinhole camera and an XUV spectrometer. The results are compared with an argon plasma based on a gas puff target operated under the same experimental conditions showing an increase of the brilliance by a factor of 84. By changing the capillary geometry from a constant diameter to a convergent shape the flow speed of the filament was significantly increased up to 250 mms, facilitating the operation at higher repetition rates.     

Extraction of ions from a plasma source and formation of beams

The current of ions extracted from a plasma source has been measured as a function of extraction voltage U _e . Comparison of the obtained characteristics to theoretical predictions has shown that the experimental data agree with the Child-Langmuir theory only within a certain range of U _e . The results of our measurements and computer simulation of the ion-beam profile allowed the assessment of the parameters of the ion-emitting surface and the average ion energy in the plasma of the source under study.     

Surface analysis using a new plasma assisted desorption/ionisation source for mass spectrometry in ambient air

The authors report on a modified micro-plasma assisted desorption/ionisation (PADI) device which creates plasma through the breakdown of ambient air rather than utilising an independent noble gas flow. This new micro-PADI device is used as an ion source for ambient mass spectrometry to analyse species released from the surfaces of polytetrafluoroethylene, and generic ibuprofen and paracetamol tablets through remote activation of the surface by the plasma. The mass spectra from these surfaces compare favourably to those produced by a PADI device constructed using an earlier design and confirm that the new ion source is an effective device which can be used to achieve ambient mass spectrometry with improved spatial resolution.