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.     

A forevacuum plasma source of pulsed electron beams

A plasma electron source designed for generation of a pulsed wide-aperture electron beam in the forevacuum pressure range (5–20 Pa) is described. The source is based on the use of a hollow-cathode glow discharge. At an accelerating voltage of 20 kV, a current pulse length of 100 μs, and a pulse repetition rate of 10 Hz, the electron beam current is 100 A, and the maximum density of the beam pulse power is 10 J/cm². The obtained parameters of the electron beam and the features of the source functioning in the forevacuum pressure range show that this source can be used to good effect to modify the surface properties of nonconducting materials.     

Novel methods for improvement of a Penning ion source for neutron generator applications

Penning ion source performance for neutron generator applications is characterized by the atomic ion fraction and beam current density, providing two paths by which source performance can be improved for increased neutron yields. We have fabricated a Penning ion source to investigate novel methods for improving source performance, including optimization of wall materials and electrode geometry, advanced magnetic confinement, and integration of field emitter arrays for electron injection. Effects of several electrode geometries on discharge characteristics and extracted ion current were studied. Additional magnetic confinement resulted in a factor of two increase in beam current density. First results indicate unchanged proton fraction and increased beam current density due to electron injection from carbon nanofiber arrays.     

Generation of high charge state metal ion beams by electron cyclotron resonance heating of vacuum arc plasma in cusp trap

A method for generating high charge state heavy metal ion beams based on high power microwave heating of vacuum arc plasma confined in a magnetic trap under electron cyclotron resonance conditions has been developed. A feature of the work described here is the use of a cusp magnetic field with inherent "minimum-B" structure as the confinement geometry, as opposed to a simple mirror device as we have reported on previously. The cusp configuration has been successfully used for microwave heating of gas discharge plasma and extraction from the plasma of highly charged, high current, gaseous ion beams. Now we use the trap for heavy metal ion beam generation. Two different approaches were used for injecting the vacuum arc metal plasma into the trap--axial injection from a miniature arc source located on-axis near the microwave window, and radial injection from sources mounted radially at the midplane of the trap. Here, we describe preliminary results of heating vacuum arc plasma in a cusp magnetic trap by pulsed (400 μs) high power (up to 100 kW) microwave radiation at 37.5 GHz for the generation of highly charged heavy metal ion beams.     

Magnetic multipole line-cusp plasma generator for neutral beam injectors

The magnetic multipole line-cusp device developed by MacKenzie and associates has been adapted for use as a neutral beam ion source. It has produced high-density, large volume, quiescent, uniform hydrogen plasmas, which makes it a potential candidate for use as a plasma generator for neutral beam injectors. The device is a water-cooled cylindrical copper discharge chamber (25 cm in diameter by 36 cm long) with one end enclosed by a set of extraction grids with a 15-cm-diam multi-aperture pattern. The chamber wall serves as an anode and is surrounded by an external system of rare-earth cobalt magnets arranged in a line-cusp geometry of 12 cusps; plasma is produced by electron emission from a hot cathode assembly. This source has achieved extracted beam currents of 12 A at 18.5 kV, radial plasma density uniformities of +/-5% over a 15-cm diameter, noise levels of less than +/-0.5%, and arc efficiencies (beam current/arc power) of 0.6 A/kW.     

Increase in the Charge State of the Uranium Ion Beam Generated by the MEVVA Ion Source

The Metal Vapor Vacuum Arc (MEVVA) ion source and its modifications are investigated at the Institute of Theoretical and Experimental Physics (ITEP). In a series of the experiments, the possibility of increasing the charge state of the generated uranium ion beam was revealed. The charge state increases as a result of developing a high-current vapor vacuum arc discharge from the source cathode to an auxiliary anode located in an increasing axial magnetic field. The uranium ion beam with a total current of 150 mA was obtained, U⁷⁺ uranium ions being 10% of the current.     

Development of a low-energy and high-current pulsed neutral beam injector with a washer-gun plasma source for high-beta plasma experiments

We have developed a novel and economical neutral-beam injection system by employing a washer-gun plasma source. It provides a low-cost and maintenance-free ion beam, thus eliminating the need for the filaments and water-cooling systems employed conventionally. In our primary experiments, the washer gun produced a source plasma with an electron temperature of approximately 5 eV and an electron density of 5 × 10(17) m(-3), i.e., conditions suitable for ion-beam extraction. The dependence of the extracted beam current on the acceleration voltage is consistent with space-charge current limitation, because the observed current density is almost proportional to the 3∕2 power of the acceleration voltage below approximately 8 kV. By optimizing plasma formation, we successfully achieved beam extraction of up to 40 A at 15 kV and a pulse length in excess of 0.25 ms. Its low-voltage and high-current pulsed-beam properties enable us to apply this high-power neutral beam injection into a high-beta compact torus plasma characterized by a low magnetic field.     

An experimental setup for exciting semiconductors and dielectrics with picosecond electron-beam and electric-field pulses

An experimental facility for forming high-voltage pulses with amplitudes of 30–250 kV and durations of 100–500 ps and electron beams with a current density of up to 1000 A/cm² is described. The facility was built using the principle of energy compression of a pulse from a nanosecond high-voltage generator accompanied by the subsequent pulse sharpening and cutting. The setup is equipped with two test coaxial chambers for exciting radiation in semiconductor crystals by an electron beam or an electric field in air at atmospheric pressure and T = 300 K. Generation of laser radiation in the visible range under field and electron pumping was attained in ZnSSe, ZnSe, ZnCdS, and CdS (462, 480, 515, and 525 nm, respectively). Under the exposure to an electric field (up to 10⁶ V cm^?1), the lasing region was as large as 300–500μm. The radiation divergence was within 5°. The maximum integral radiation power (6 kW at λ = 480 nm) was obtained under field pumping of a zinc selenide sample with a single dielectric mirror.     

Gas discharge ion source. I. Duoplasmatron

The effects of the plasma expansion cup on the operation of a duoplasmatron ion source have been investigated by measuring the total ion current and the distributions of the ion energy, mass, and current density. A copper expansion cup did not affect the magnetic field near the anode of the ion source and consequently the ion current density distribution was sharply peaked near the center of the cup. Ion energy distributions were approximately symmetrical about anode potential. The dominant ionic species were D(+) (3) and D(+) at low and high arc currents, respectively. Changes in the electrical potential of the copper cup with respect to the anode produced negligible changes in the above data. A mild steel plasma expansion cup caused the magnetic field to diverge and intercept the cup walls, resulting in ion current density distributions that were flatter and more amenable to focusing than the ones with the copper cup. With the steel cup at anode potential, the ion mass distribution was similar to that from the copper cup; however, the ion energy distribution was asymmetrical about the anode potential with a peak about 10-20 V above anode potential. The total ion current from this mode of operation was about one-third the value from the copper cup. If the steel cup assumed floating potential, about 50 V below anode potential, the total current increased to the level observed from the copper cup and the ion energy distribution was similar to that observed with the copper cup but the current density distribution was much flatter than that of the copper cup. The ion mass distribution was 60%-70% atomic ions over the entire arc current range investigated. Based on these data, a modified plasma expansion cup was designed with tapered steel walls lined with a boron nitride insert. The overall performance of the duoplasmatron ion source with this cup was superior to any of the previous three modes of operation. The improved design uses a molybdenum anode insert which is far superior to copper in regard to erosion over extended operating times. A total beam current of 200 mA was produced at an arc current of 24 A.     

A source of broad homogeneous beams of low-energy (∼0.5 keV) gas ions

A source of gas ions (argon, oxygen, nitrogen, etc.), the operating principle of which is based on the use of a glow discharge in an electrode system of a wide-aperture hollow cathode and anode in a magnetic field, is described. The exit aperture diameter of the hollow cathode, increased up to a size close to the ion beam diameter (10 cm), ensures the uniform ion emission of the plasma generated in the discharge region near the anode. A decreased angular divergence or increased ultimate ion-beam current density is achieved by a change in the potential drop in the space charge sheath between the plasma and the ion optics. The source generates broad (50 cm²) slightly diverging (ω/2∼3°–5°) ion beams with energies of 300–1000 eV at a beam current density of ∼0.5 mA/cm².     

A Plasma-Cathode Electron Source for Focused-Beam Generation in the Fore-Pump Pressure Range

A plasma electron source is described that forms a focused beam in the range of fore-pump pressures. Plasma is generated in a hollow-cathode discharge. Electrons are extracted through a single emission hole in the anode. The source provides an electron-beam current of up to 0.1 A and an energy of up to 20 keV. The beam diameter at the half-height of the current-density distribution is ≤1.4 mm, and the beam-power density is as high as 1.5 kW/mm².     

A facility for metal surface treatment with an electron beam

A design for a facility for the surface treatment of metal samples is described, and the results from investigating the source of a high-current low-energy electron beam are presented. The electron beam, which has a current as high as 300 A, a pulse duration of 30 µs, and a pulse repetition rate of up to 10 Hz, is formed in a plasma-cathode gas-filled diode at an accelerating voltage of 20 kV. The space-charge compensated electron beam is transported a distance of 20 cm in a longitudinal magnetic field to the region of its interaction with a solid body. At a current density as high as 100 A/cm², the power density produced by the beam is sufficient for the metal surface to be melted in the duration of one or several pulses. Samples can be replaced in the facility without breaking the vacuum.Translated from Pribory i Tekhnika Eksperimenta, No. 1, 2005, pp. 135–140.Original Russian Text Copyright © 2004 by Koval, Shchanin, Devyatkov, Tolkachev, Vintizenko.     

Density measurements using coherence imaging spectroscopy based on Stark broadening

A coherence imaging camera has been set up at Pilot-PSI. The system is to be used for imaging the plasma density through the Stark effect broadening of the H(γ) line. Local density values are then obtained by the Abel inversion of the measured interferometric fringe contrast. This report will present the instrument setup and proof-of-principle demonstration. The inverted spatial electron density profiles obtained near the cascaded arc source of Pilot-PSI in discharges with axial magnetic field of B=0.4?T are compared with an independent measurement of electron density by Thomson scattering and good agreement is found.     

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.     

A source of broad electron beams with a self-heated hollow cathode for plasma nitriding of stainless steel

The principle of operation and characteristics of a broad electron beam source based on the discharge with a self-heated hollow cathode and widened anode part are described. The source is intended for the ion nitriding of metals in the electron beam plasma. The influence of the current density (1–7 mA/cm²) and ion energy (0.1–0.3 keV) on the nitriding rate of the 12X18H10T austenitic stainless steel is studied. It is shown that the maximal nitriding rate is reached by the combining of the minimal bias voltage across the samples (100 V) and maximal ion current density, which ensures the dynamic oxide layer sputtering on the sample surface. The electron source, in which electrons are extracted through a stabilizing grid in the direction normal to the axis of the hollow cathode, ensures the radially divergent electron beam formation with a 700-cm² initial cross section, a current of up to 30 A, and initial electron energy of 0.1–0.5 keV. The source stably operates at nitrogen-argon mixture pressures of up to 3 Pa.     

The design of an electron gun switchable between immersed and Brillouin flow

An electron gun, which can be switched from immersed flow to Brillouin flow during operation, may have advantages for charge breeders as well as for electron beam ion sources and traps (EBISTs). For EBISTs this allows to change the current density according to the repetition frequency and charge state, for charge breeders and EBISTs a lower current density in immersed flow provides higher acceptance for injected ions, while the higher current density in Brillouin flow results in shorter breeding times and a lower emittance for the extracted beam. Therefore, we have designed such a gun for an EBIS with 5 T central magnetic field and without the use of iron and moving the gun. The gun was placed in the axial fringing field of the 5 T solenoid in such a position that a gate valve can be placed between the gun and the cryostat to allow for simple maintenance. The field at the cathode surface turned out to be only 0.05 T, which is not enough to focus 50 A∕cm(2) at a few kV. However, if a small normal conducting solenoid is placed over the vacuum tube in position of the gun, a field of 0.1 T may be obtained. With this the use of LaB(6) as cathode material results in a magnetic compression of 44 and therewith in a focused current density in the trap region of more than 2000 A∕cm(2). By reversing the current in the gun solenoid the cathode field can easily compensated to zero. By proper design of the electrodes and the compression region, the gun will be able to deliver a beam in Brillouin flow. While this is interesting by itself--remember the "super-compression" reported on CRYEBIS-I--any magnetic field between zero and the value for immersed flow will result in an electron beam with a wide range of adjustable high current densities. The design tools used have been INTMAG(C) for the calculation of magnetic fields, EGN2(C) for the simulation of the gun and ANALYSE(C) for detailed analysis of the results (for more information see www.egun-igun.com).     

焊接电流影响GMAW双丝焊电弧等离子体的数值模拟研究

基于电磁学理论和流体力学理论,建立熔化极气体保护焊(Gas metal arc welding,GMAW)双丝焊焊接电弧等离子体三维数学模型,利用流体力学软件Fluent对其进行求解。重点研究焊接电流对GMAW双丝焊电弧等离子体行为的影响规律,获得了电弧温度、电流密度、热通量、磁场分布等结果。研究发现,随着焊接电流的变化,电弧等离子体形状变化显著。随着焊接电流的增大,电弧最高温度和电弧偏转角随之增大,电流密度和工件表面热通量由双峰分布转变为单峰分布,并且热通量峰值随焊接电流的增大而增大。此外,随着焊接电流的增大,磁感应强度和磁场力随之最大,磁场分布由独立两个磁场向耦合磁场转变。为有效、定量地证明模拟结果准确性,开展焊接试验,利用高速摄像监测电弧行为,利用光谱测温测量电弧温度。结果表明模拟结果同试验结果吻合良好,研究结果为合理选择GMAW双丝焊焊接电流参数提供理论依据。     

Calculation of the variable-profile electron beam for electron coolers

Interaction of an electron beam with a cooled ion beam makes it possible to reduce its phase volume, perform accumulation of particles, and suppress various “heating” effects. The electron beam can also be used as a target for an electron-ion recombination reaction, which offers a chance to carry out atomic physics experiments and ensure slow uniform extraction of the ion beam from the storage ring. A high-perveance electron beam with a variable profile is required for effective cooling, while a high current density and a low energy of transverse motion of electrons in the beam is needed for extraction by means of recombination. It is shown that a convex cathode placed in a magnetic field can be used to form such a beam. A high current density can be attained with this shape of the cathode, but additional efforts must be focused on optimizing the gun’s optics in order to obtain a low energy of transverse motion of particles. Since ions repeatedly pass through the cooling section during their lifetime at different values of the betatron oscillation phase, the rates of recombination and cooling are dependent on the rms electron velocity averaged over the volume in which the beam interaction occurs. The proposed design of the gun with a convex cathode 10.2 mm in diameter ensures formation of a variable-profile electron beam with a nominal current of 1 A and a current density of 1.2 A/cm². The rms energy of Larmor gyration of electrons at the exit from the gun, averaged over the beam cross section (the “transverse” temperature) is 1 eV. A focusing electrode that forms the Pierce optics near the edge of the cathode, an electrode controlling the beam profile, and an anode are included in the optics of the electron gun.     

Electrical shielding box measurement of the negative hydrogen beam from Penning ion gauge ion source

The cold-cathode Penning ion gauge (PIG) type ion source has been used for generation of negative hydrogen (H(-)) ions as the internal ion source of a compact cyclotron. A novel method called electrical shielding box dc beam measurement is described in this paper, and the beam intensity was measured under dc extraction inside an electrical shielding box. The results of the trajectory simulation and dc H(-) beam extraction measurement were presented. The effect of gas flow rate, magnetic field strength, arc current, and extraction voltage were also discussed. In conclusion, the dc H(-) beam current of about 4 mA from the PIG ion source with the puller voltage of 40 kV and arc current of 1.31 A was extrapolated from the measurement at low extraction dc voltages.     

Development of a plasma generator for a long pulse ion source for neutral beam injectors

A plasma generator for a long pulse H(+)/D(+) ion source has been developed. The plasma generator was designed to produce 65 A H(+)/D(+) beams at an energy of 120 keV from an ion extraction area of 12 cm in width and 45 cm in length. Configuration of the plasma generator is a multi-cusp bucket type with SmCo permanent magnets. Dimension of a plasma chamber is 25 cm in width, 59 cm in length, and 32.5 cm in depth. The plasma generator was designed and fabricated at Japan Atomic Energy Agency. Source plasma generation and beam extraction tests for hydrogen coupling with an accelerator of the KSTAR ion source have been performed at the KSTAR neutral beam test stand under the agreement of Japan-Korea collaborative experiment. Spatial uniformity of the source plasma at the extraction region was measured using Langmuir probes and ±7% of the deviation from an averaged ion saturation current density was obtained. A long pulse test of the plasma generation up to 200 s with an arc discharge power of 70 kW has been successfully demonstrated. The arc discharge power satisfies the requirement of the beam production for the KSTAR NBI. A 70 keV, 41 A, 5 s hydrogen ion beam has been extracted with a high arc efficiency of 0.9 -1.1 A/kW at a beam extraction experiment. A deuteron yield of 77% was measured even at a low beam current density of 73 mA/cm(2).