Wide gas-ion beam source based on an arc discharge in a nonuniform magnetic field

The construction of an ion source based on a low-pressure arc with a screened cathode spot is described. The source is ignited by an auxiliary glow discharge in a magnetron electrode system. Ions are extracted from the plasma of the anode part of the arc, generated in a reflective electrode system. The effect of the magnetic induction and the emitter electrode potential on the parameters of the anode plasma was investigated, and the conditions required for generation of a dense uniform plasma, ion emission from which gives beams of ions of nitrogen, argon, oxygen, other gases with cross section 100 cm², current density 10 mA/cm² and nonuniformity of the plasma distribution in the beam cross section 10%, were determined. The formation of wide and converging beams with ion energies up to 50 keV by multiple-aperture ion-optic systems were examined. The source operates in the periodic-pulse mode. The repetition frequency of 1-msec pulses can be regulated from 0 to 50 sec^–1 giving an average beam current of up to 50 mA. It is intended for use in technologies for modification of the surface properties of materials and deposition of thin films. A cold cathode makes possible prolonged operation of the source with chemically active gases.Institute of Electrophysics, Ural Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshykh Uchebnykh Zavedenii, Fizika, No. 3, pp. 66–75, March, 1994.     

To the role of positive ions in plasma nitridation

The method similar to that of determining the asymmetric componentf ₁ of electron distribution function was used to prove whether the nitrogen ions produced in discharge may be the very particles which directly influence magnesium nitridation in glow discharge. The amounts of created magnesium nitride on surfaces facing the anode and the cathode, and positive ion current to the plane double-probe were measured. It follows from experimental results that positive ions from bulk plasma are not decisive for nitride formation.The authors would like to thank Dr. V.Krejí and Dr. K.Maek for helpful discussions and critical notices.     

Feasibility study on high current ion beam extraction from anode spot plasma for large area ion implantation

In this paper, we have investigated the feasibility of the high current beam extraction from anode spot plasma as an ion source for large area ion implantation. Experiments have been carried out with the ambient plasma produced by inductive coupling with radio-frequency (RF) power of 200 W at the frequency of 13.56 MHz. Anode spot plasmas are generated near the extraction hole of 2 mm in diameter at the center of a bias electrode whose area exposed to the ambient plasma can be changed. It is found that the maximum ion beam current is extracted at the optimum operating pressure at which the area of bias electrode exposed to ambient plasma is fully covered with the anode spot plasma whose size is dominantly determined by the operating pressure for given gas species. It is also observed that the extracted ion beam current increases nonlinearly with the bias power due to the changes in size and shape of the anode spot plasma. With the well-established anode spot plasma operating at the optimum gas pressure, we have successfully extracted high current ion beam of 6.4 mA (204 mA/cm²) at the bias power of 22 W (∼10% of RF power), which is 43 times larger than that extracted from the plasma without anode spot. Based on the experimental results, criteria for electrode design and operating pressure for ion beam extraction from larger extraction aperture are suggested. In addition, the stability of anode spot plasma in the presence of ion beam extraction through an extraction hole is discussed in terms of the particle balance model.     

Helium ion distributions in a 4 kJ plasma focus device by 1 mm-thick large-size polycarbonate detectors

Helium ion beam profile, angular and iso-ion beam distributions in 4 kJ Amirkabir plasma focus (APF) device were effectively observed by the unaided eyes and studied in single 1 mm-thick large-diameter (20 cm) polycarbonate track detectors (PCTD). The PCTDs were processed by 50 Hz–HV electrochemical etching using a large-size ECE chamber. The results show that helium ions produced in the APF device have a ring-shaped angular distribution peaked at an angle of ∼±60°$\sim \pm 60\mathrm{°}$ with respect to the top of the anode. Some information on the helium ion energy and distributions is also provided. The method is highly effective for ion beam studies.     

Nonlinear interaction of a modulated beam with plasma

Nonlinear evolution of h. f. instabilities excited by a premodulated electron beam in a magnetized plasma is investigated both theoretically and experimentally. Only the erenkov type of excitation (k_¦|v_b) of the upper branch of the electron plasma oscillations has been observed. The dynamics of excitation of the quasistationary fundamental wave (having the frequency of modulation) has been determined numerically. The wave absorption has been included into the theoretical model through an effective collision frequency. Numerical results agree well with the measured evolution of the amplitude and of the phase velocity of the fundamental wave along the system, as well as with the beam distribution functions. The observed bunching of beam electrons and characteristic features of plasma electrons heating are also reported. Broadening of the frequency spectrum and the occurrence of satellite waves with lower phase velocities have been observed downstream. Physical mechanism of spantaneous excitation of these satellites is suggested and their role in the process of the beam relaxation is discussed. More detailed studies of the nonlinearly excited waves have been performed by modulating the beam at two frequencies.It is a pleasure for us to thank Dr .Körbel who has kindly performed the numerical calculations.     

Laser-produced copper ion energy spectrum employing Thomson scattering technique

Investigations were performed on laser-assisted ion emission when a copper target was irradiated with a Nd:YAG laser (1.064 μm 10 mJ and 1.1 MW). Charge states present in the ion core emitted from plasma were determined employing Faraday cup arrangement using a four-channel 500 MHz Digital Storage Oscilloscope YOKOGAWA DL 1740. The Thomson parabola scattering (TPS) technique was used to measure the energy of ions emitted from plasma. Singly charged positive ions were found to be in excessive amount. For the energy analysis, the ion beam was collimated using a pinhole arrangement. The collimated beam was then made to pass through a uniform magnetic field of 0.4 T. A solid-state nuclear track detector PM-355 was used to register the ion tracks. The energy of ions, found to be in the range of 9–50 keV. The ion energy spectra d ² N/dEdΩ show a decreasing trend with increasing ion energy. The empirical relation dN/dE ∞ E ^?n fits well with the experimental data at higher values of energy, i.e., greater than 20 keV.     

Distribution of the amplitude of the magnetic potential of diffractive beams generated in a ferrite slab by a surface spin wave incident on a slit in an opaque screen

The total magnetic potential generated in the far field of a ferrite slab as a result of a plane noncollinear surface spin wave incident on a slit in an opaque screen is investigated. The dependence of the potential amplitude from the polar angle in the plane of a ferrite slab is calculated for different orientations of the screen with relative to an external magnetic field magnetizing the slab. It is found that two diffractive beams are generated in the slab as a result of spin diffraction on the slit. The angular width of each beam depends largely on the slit’s orientation and can be greater or smaller than value λ _n /D (where D is the slit’s width and λ _n is the length of the spin wave corresponding to each beam).     

Generation of soft X rays in a vircator with exploding anode foil

A soft X-ray generator is designed on the basis of a vircator the plasma anode of which is formed by electrical explosion of anode foil. The intensity of soft X-ray radiation (E _γ > 20 eV) produced by vircators with a metal and plasma anode is measured. Microwave pulses indicating the presence of a virtual cathode in the plasma beam are detected.     

Characteristic features of the emission properties of pulsed broad-beam ion and plasma sources utilizing the evaporation of metal by a vacuum arc

An experimental confirmation was obtained of the anode potential fall effect in pulsed broad-beam ion and plasma sources utilizing the evaporation of metal by a vacuum arc. An increase in the overall voltage across the arc discharge was discovered. The investigations demonstrated that the magnitude of the positive anode fall depends on the structural features of the ion source and are determined by the ratio of the plasma flux directed onto the lateral surface of the anode to the total plasma flux from the cathode spot. It was established that the anode fall effect is controlled and makes it possible to influence the homogeneity of the ion current distribution over the beam cross section, the efficiency of extracting ions from the plasma, and the charge composition of the ion flux.Scientific-Research Institute of Nuclear Physics, Polytechnic University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 82–92, February, 1994.     

Neutralization of an ion beam from the end-Hall ion source by a plasma electron source based on a discharge in crossed E × H fields

The possibility of using a plasma electron source (PES) with a discharge in crossed E × H field for compensating the ion beam from an end-Hall ion source (EHIS) is analyzed. The PES used as a neutralizer is mounted in the immediate vicinity of the EHIS ion generation and acceleration region at 90° to the source axis. The behavior of the discharge and emission parameters of the EHIS is determined for operation with a filament neutralizer and a plasma electron source. It is found that the maximal discharge current from the ion source attains a value of 3.8 A for operation with a PES and 4 A for operation with a filament compensator. It is established that the maximal discharge current for the ion source strongly depends on the working gas flow rate for low flow rates (up to 10 ml/min) in the EHIS; for higher flow rates, the maximum discharge current in the EHIS depends only on the emissivity of the PES. Analysis of the emission parameters of EHISs with filament and plasma neutralizers shows that the ion beam current and the ion current density distribution profile are independent of the type of the electron source and the ion current density can be as high as 0.2 mA/cm² at a distance of 25 cm from the EHIS anode. The balance of currents in the ion source-electron source system is considered on the basis of analysis of operation of EHISs with various sources of electrons. It is concluded that the neutralization current required for operation of an ion source in the discharge compensation mode must be equal to or larger than the discharge current of the ion source. The use of PES for compensating the ion beam from an end-Hall ion source proved to be effective in processes of ion-assisted deposition of thin films using reactive gases like O₂ or N₂. The application of the PES technique makes it possible to increase the lifetime of the ion-assisted deposition system by an order of magnitude (the lifetime with a Ti cathode is at least 60 h and is limited by the replacement life of the deposited cathode insertion).     

Corpuscular diagnostics of a hollow-cathode discharge-III. The metal-ions-regime evolution

The variations in time of mass spectra of ions, extracted from the hollow-cathode discharge in the regime of the intensive sputtering of the cathode material were measured. The mass spectrum changes in time conspicuously. From the results of measurements a distinct anisotropy of ion beam is inferred. The discharge turns into a metal-ions regime.The helpful discussions with Dr. J. Musil are gratefully acknowledged.     

Pulse intense metal-ion diode with a vacuum arc plasma anode

An intense pulsed ion beam of metal was extracted from a magnetically insulated ion diode operated in a mode of plasma prefill generated from a vacuum arc discharge, anode plasma source. With this ion diode, an intense metal-ion beam of a high melting-point metal (Ta) was obtained. A variety of operational modes appeared, depending on the amount of plasma in the diode gap at the initiation of the high-voltage pulse. The energy, current, and duration time of the ion beam were 20~100 keV, ~1 kA, and 1 μs, respectively. Measurements of ions were performed with an ion energy analyzer or a biased ion collector located at the end of a long drift tube and a Thomson parabola ion spectrometer. The Ta ions in the first to fifth states of ionization were detected accompanied by C⁺, O⁺, F⁺, and H⁺ . A Ta ion beam current of about half the total ion flux was obtained in this experiment     

Simulation of the Field Emission Arrays with Parallel Wedge Emitter, Gates and Co-Planar Lens

Using the particle-in-cell (PIC) simulation code MAGIC, the wedge emitter, parallel gate and anode with and without co-planar lens have been simulated. The electron beam streamlines and the X-V_x phase space have been evaluated, which show that the co-planar lens focuses the electron. Simulation results are presented for a single FEA's cell with the anode biased at 500V and spaced 100m from the cathode, which indicated that the electron beam width at anode is about 60.2m for without lens FEAs, after add the lens with –70V, the electron beam width will be decrease to 8.1m, meanwhile the maximum transverse velocity will decrease from ±1×10⁶m/s to ±1.46×10⁵m/s.     

FDTD Simulation of Electromagnetic Pulse Interaction with a Switched Plasma Slab

This paper deals with the Finite Difference Time Domain (FDTD) simulation of interaction of an electromagnetic wave with a switched plasma slab. In formulating the simulation the well-known concepts of (a) total-field/scattered-field formulation (b) and PML lattice truncation are adapted to suit the simulation under consideration.FDTD is particularly well suited to handle the switched (time-varying) medium (including sudden switching) since the time varying parameters of the medium can be easily interpreted in the algorithm. The technique is applied to the difficult problem of interaction of an electromagnetic pulse source wave of frequency ₀ and a gaussian envelope with a newly created plasma slab of time-varying and space varying electron density profile. The creation of a pulse of Wiggler magnetic field in the slab is illustrated.     

Heavy Ion Beam Probe Plasma Diagnostic System for the Deep Magnetic Well Lite Device

A heavy ion beam probe plasma diagnostic system has been developed for the Laser Initiated Target Experiment (LITE) at UTRC. This is the first application of ion beam probing to a plasma confined by a strongly three dimensional magnetic field. The deep magnetic well, minimum-B field produced by the "baseball" magnet coil results in complex trajectories and severe defocusing of both the injected primary beam and detected secondary beam. Spatial resolution can be maintained by aperturing the entrance slit to the detector or installing compensating ion optics. The system is capable of space and time resolved measurements of plasma density and space potential near the central region of the mirror-confined plasma.     

Anode plasma structure in a gas discharge with neutral density depleted by ionization

We consider the anode plasma structure in a gas discharge with density of neutral atoms (neutrals) depleted by strong ionization. We obtain analytical solutions of the quasi-neutrality equation for the potential distribution and a condition for the existence of anode plasma in the one-dimensional case for arbitrary potential dependences of the neutral depletion frequency and the electron density. We consider the special cases of a constant neutral depletion frequency, ionization by Maxwellian electrons, and ionization by an intense electron beam under the conditions of collisionless ion motion and Boltzmann thermal electron distribution. The solutions for the first two cases at zero depletion parameter, i.e., at constant gas density, match those obtained in [1] by a power series expansion. In the case of ionization by Maxwellian electrons, the formation of anode plasma at reasonable working-gas flow rates is shown to be possible only at a fairly high electron temperature (if, e.g., xenon is used as the working gas, then T _e ≥ 5 eV). Steady-state solutions of the quasi-neutrality equation under ionization by an intense electron beam exist only if the ratio of the electron beam density to the maximum thermal electron density does not exceed a certain limiting value.     

Generation of a submillisecond electron beam with a high-density current in a plasma-emitter diode under the conditions of open plasma boundary emission

The generation of a 250-μs-wide electron beam in a plasma-emitter diode is studied experimentally. A plasma was produced by a pulsed arc discharge in hydrogen. The electron beam is extracted from a circular emission hole 3.8 mm in diameter under open plasma boundary conditions. The beam accelerated in the diode gap enters into a drift space in the absence of an external magnetic field through a hole 4.1 mm in diameter made in the anode. The influence of electron current deposition at the edge of the anode hole on the beam’s maximum attainable current, above which the diode gap breaks down, is studied for different accelerating voltages and diode gaps. The role of processes occurring on the surface of the electrodes is shown. For an accelerating voltage of 32 kV, a mean emission current density of 130 A/cm² is achieved. The respective mean strength of the electric field in the acceleration gap is 140 kV/cm. Using the POISSON-2 software package, the numerical simulation of the diode performance is carried out and the shape of steady plasma emission boundaries in the cathode and anode holes is calculated. The influence of the density of the ion current from the anode plasma surface on the maximum attainable current of the electron beam is demonstrated.     

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介绍了一种低功率圆柱形阳极层离子源的工作特性和束流分布特性。离子源正常工作参数范围为工作电压200～1200V,放电电流0.1～1.4A,工作气压1.9×10-2～1.7×10-1Pa,气体流量5～20sccm。离子源有两个工作状态：发散状态和准直性状态。     

Plasma Emission Mechanism from Duoplasmatron Hydrogen Arc?theoretical Model of the Arc

The mechanism of plasma emission from the duoplasmatron (DPT) is studied in terms of a model involving a "potential hump" and following the course of an ion (along the magnetic-field lines which are obtained by computational simulation) in moving towards and through the anode nozzle. The analysis of this model indicated the necessity for the "potential hump" in the arc and this corroborated the plasma potential measurements by single probe [14]. The plasma output is determined by the rate of production of ions, which is confined into the region defined by magnetic-field line on the anode side of the "potential hump." In view of this, estimated and measured values of the total output seem to be in good agreement. Therefore post-ionization in the anode cup as proposed by some researchers [8], [16] seems not to be necessary to account for the plasma output.     

Generation of Multiply Charged Ions in the Plasma of a Vacuum Arc Discharge

This paper presents the results of a study on the generation of multiply charged ions in the plasma of a vacuum arc discharge. The average charge of ions in the plasma is increased by using a strong magnetic field, a current burst, or an accelerated electron beam. The results of measurements of the ion charge distribution for each case are reported.