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The mechanism of ion extraction from flowing plasma using an external electrostatic field is investigated experimentally and computationally. The plasma is generated by electron impact ionization of a copper atomic beam. The plasma, along with the atomic beam vapor, flows upward and ions from the plasma are extracted using an external electrostatic field set up by a pair of parallel-plate electrodes. The extraction mechanism is studied using in-house developed hybrid 2D Particle-In-Cell (2D-PIC) code. The experimental results are found to be in good agreement with the computationally obtained values.

Ripple in HV power supply is inevitable. In this current work, the effect of ripple present in the accelerating voltage on the dynamics of an electron beam from a strip-type electron gun is investigated. A comparative study has been performed by 3D simulation of the electron trajectories from the strip electron gun using SIMION 7 for AC and DC modes of filament-heating. In both the cases, it has been found that the average width of the electron beam increases considerably due to its width-wise oscillation leading to a decrease in its average power density even in the presence of about 1.2% rms ripple in the accelerating voltage. In the AC mode of filament-heating, the beam oscillates along the length due to the filament current-generated magnetic field. Thus, in case of AC filament-heating, length- and width-wise oscillations result in the formation of a larger molten pool required for processing large raw material for metal purification purposes. The inherent ripple in the accelerating voltage is shown to be useful in avoiding material sputtering, yet maintaining a high evaporation rate.

The method of Electron Beam-Physical Vapour Deposition (EB-PVD) for handling large substrates is well established in the metallurgical industry, where sweeping axisymmetric electron guns or multiple pencil guns are routinely used to cover a large target area. The non-uniformity in current density in those methods can be overcome, to a large extent, by using the strip-type electron gun. In this paper, we propose to use an AC-heated strip-type electron gun to cover large target areas. The magnetic field generated by the alternating filament current oscillates the beam in a direction parallel to the filament length, thereby eliminating the need for applying an external electric or magnetic field for sweeping the beam. The non-uniformity in the current density within the strip electron beam, arising due to finite length of the filament, is reduced by the use of dummy filaments on both ends of the active filament. These results are supported by electron trajectory simulations.

A 3-D Direct Simulation Monte Carlo (DSMC) code has been developed to study the vapour characteristics of atomic species. This model needs to be verified with experimental results. Experiments have been conducted with free jet of copper using electron beam source and the flux distribution data have been obtained under different experimental conditions. For better statistics, the Direct Simulation Monte Carlo (DSMC) code was parallelised to run on parallel system. The experimental results from circular and a slit source (Kn varies from 0.47 to 0.083) have been compared with Direct Simulation Monte Carlo (DSMC) results. The results have shown excellent agreement. From the trend of the flux distribution curves, it is clear that with lower Kn, more uniform coating can be expected.

Photoplasma is produced through multi-step resonant photoionization method by shining the laser pulses onto a collimated atomic beam. It has finite size having a sharp density gradient at its boundary. It is created within the duration of laser pulse (~10 ns) while it lasts for few tens of micro-seconds. During its decay in an external electrostatic field, the photoplasma passes through various physical phenomena happened along the direction of the electric field. The transient responses of photoplasma to the external electric field and its temporal evolutions are studied using a one dimensional model based on standard particle-in-cell (PIC) technique. The various processes like relaxation of mono-energetic electrons, spatial and temporal variations in plasma potential, plasma-sheath formation, charge particles distribution near the plasma-sheath boundary, motion of plasma-sheath boundary, expansion of the finite-width photoplasma and collections of charge particles at the boundaries (i.e. electrodes) are investigated and discussed.

We present results on the spatial distribution of copper vapour as a function of temperature, from a 2D evaporating source generated using 130 mm strip electron beam at aspect ratio >3. At this aspect ratio vapour flow is expected to appear approximately as a point source flow. The 2D evaporating source during these studies can be described in terms of inverse Knudsen number (1/ K n ) that is proportional to source temperature, ranging from 0.75 to 6.67. These experimental results could be fitted with accuracy of ±5% using a spatial distribution function with different beaming coefficients along the width and the length of a 2D source. It is observed that the beaming exponent along the width of a 2D source saturates at about 2, which is marginally higher than that observed for the aspect ratio in the range of 1 to 2 for the similar range of 1/ K n , whereas, the beaming exponent along the length direction of a 2D source was observed to increase up to 6.34, which is substantially higher than that observed at the aspect ratio in the range of 1–2 for the similar range of 1/ K n . These results clearly indicate that, for given evaporating source conditions, the widthwise atomic collisions, collimation of atomic beam and beaming exponent along the width remains constant. At the same time lengthwise collisions, atomic beam collimation and hence beaming coefficient do not freeze and the wedge-shaped atomic beam does not run out of collisions in the lengthwise direction even at aspect ratio >3. Thus, the atomic vapour from a 2D source does not attain the free molecular regime even at radial distance in excess of 390 mm above the source.

Strip electron guns, capable of generating two-dimensional (length⪢width) evaporating sources, are used for the application of electron beam assisted physical vapour deposition to metallurgical coating of large substrates. The collisional relaxation processes in the atomic vapour generated using such a 2D-source differ significantly from those in a point source created using axisymmetric electron gun. In order to study the influence of collision processes, an atomic beam of zirconium was generated using a 130- mm-strip electron gun and its ground electronic state population was measured in a given optical path length using a tunable diode laser based on-line absorption spectroscopic technique. These measurements were carried out as a function of vertical height from the source (114 mm×6 mm) and for different source temperatures obtained by varying electron beam powers in the range of 40–91 kW.While the experimental values of integrated atom number density were observed to match very closely with those given by reported vapour flow model at low evaporating source temperatures, they showed significant deviation at high temperatures. The results are interpreted in terms of the collisional processes in the vapour stream and indicative of the fact that the vapour expansion from 2D source never runs out of collisions.

We present results on the spatial distribution of copper vapour flux in the three-dimensional flow behaviour region under identical experimental conditions as a function of the temperature of a two-dimensional (2D) evaporating source. These experimental results clearly show that, with increasing source temperature, atomic collision processes along the length and the width of a 2D source differ, which results in a differential collimation of atomic beam which can be evaluated using different beam exponents in these directions. A generalized function describing the spatial distribution of atomic vapour from a point as well as from a 2D source and deviation from Knudsen's cosine law is presented. With this distribution function, the experimentally measured vapour flux distribution from a 2D source as a function of temperature, described in terms of Knudsen numbers ranging from 1.2 to 0.23, could be fitted to an accuracy of ±5%.

The experimental measurements of spatial distribution of copper vapour flux from a two-dimensional source (D = 10.4 mm; L = 97 mm) was carried out by impinging electron beam from 130 mm strip electron gun. The copper vapour was generated in the transition flow regime of rarefied gas dynamics and experimental measurements were carried out by using deposition technique, at locations (r), where free jet expansion is expected to show three-dimensional behaviour (DL ∼ r). Reported analytical expressions based on Knudsen's cosine law for two-dimensional sources with uniform temperature were reviewed and used for the interpretation of experimental data. The inadequacy of these expressions is pointed out by noting the systematic deviation of the calculated values from the observed ones with receding position of the vapour collector from normal line of the source. Attempts are made to interpret experimental data by dividing source area into small elemental areas and integrating contribution from each such area on to the collectors. The experimental data could be best fitted within ±5% with cos n ψ distribution with n = 1.77 and uniform source temperature of 1694 K or with n = 1.75 with temperature distribution along and across the focal strip with an average temperature of 1687 K as compared to the measured value of 1685 K.

During electron beam processing, a fraction of the incident power gets backscattered from the target surface, which can be as high as 40% of the incident beam power depending on the beam energy and atomic number of the target material. In the case of a strip electron gun, a uniform magnetic field is used for focusing and deflection of electron beam through 270°. With the strip beam (78 mm×5 mm, 36 kW), experimental results of the 2-D distribution of the backscattered electron current from copper target in its plane, parallel and perpendicular to the focal strip are presented. These results are compared with calculated data using reported energy distribution of backscattered electrons (E.H.Darlington, J. Phys. 8 (1975) 85). The integrated heat flux associated with backscattered electron is experimentally measured and compared with calculated values for incident power of 86 kW. With 12.25 kW/cm2 of incident strip beam power, the back reflected electron peak power density was observed to be 59W/cm2. This power density will be higher for high incident power densities and for targets of high atomic numbers and can be used in pre-coating treatments of substrate such as outgassing and cleaning, keeping it at elevated temperature during continuous coating process, and also for outgassing, cleaning and sharing heat load required for pre-melting of the feeder material during melting and casting.

This article discusses the simulation, design and performance of an 80 kW strip electron gun. Electrons from an electrically heated, multisegmented tantalum filament are electrostatically focused to provide a sheet of electrons in the postanode region, that when bent through 270° along a circle of radius 120 mm by a uniform magnetic field, focuses on the target. This gun has been tested up to 80 kW (45 kV×1.8 A), and delivers power densities on the target in the range of 20 kW cm−2. The linear current density is uniform up to 20%, over a focal spot of dimension 80×5 mm2. Good correspondence between filament geometry and focal spot image of the electron beam on the target has been obtained, which is desirable in applications involving metal vapor coatings. This design is scaleable along the length of the focal spot without sacrificing uniformity, which is not possible in scanning or multiple pencil-type of electron guns. Experimental measurement of gun parameters such as position of filament in relation to the cathode opening, distribution of current along the length of the beam, focal spot size, extraction efficiency, etc., along with data concerning electron beam quality as a function of various parameters, are presented. The performance of this gun under different experimental conditions, as well as the simulation and modeling using an in-house three-dimensional beam dynamics code, is discussed.

Graphite is a widely used structural material for high temperature and high vacuum applications in furnaces handling corrosive materials or plasmas. The porosity, density, dimensions, impurities along with the history of graphitization, handling and storage of graphite dictate the outgassing characteristics. Graphite plates of density 1.78 g/cc were outgassed up to 1200 °C in vacuum of the order of 5×10−5 mbar in an in-house facility. A sample of the degassed graphite was taken for Thermo-Gravimetric Analysis (TGA). The TGA of the outgassed sample shows continuous weight loss in the temperature range of 200 °C to 1200 °C, indicating a much higher temperature is required for complete removal of gases. However, it may be noted that total outgassing is a function of the dimensions of the sample. The small coupon used in the TGA studies may not exactly replicate the large graphite blocks that outgases from the surface as well as from the bulk. The behaviour of graphite plates used in the liquid metal handling furnace where the graphite was finally used further confirmed this observation. The outgassing shown by the degassed graphite can be attributed to the diffusion of the absorbed gases from the bulk as well as desorption of the chemisorbed species which requires higher activation energies and higher temperature.

Atomic Vapor Laser Isotope Separation (AVLIS) is an established method of isotope separation for various elements used in the nuclear industry. Real-time knowledge of vapor flux, density and flow velocity of the atomic beam is essential in the AVLIS process to estimate the throughput, ionization yield and laser repetition rate, respectively. Conventional techniques used in EB-PVD and thin film coating do not provide these parameters independently. The microbalance technique, on the contrary, provides atomic flux, flow velocity and atom density simultaneously. In the present work, flux and flow velocity of copper and zirconium atomic beams are measured using the microbalance technique. The atomic beams are generated by electron beam heating using a strip-type electron gun with the electron beam power ranging from 36 kW up to 100 kW corresponding to the temperature ranges of 1740 to 1950 K (Kn=0.73 to 0.08) for copper and 2606 to 3269 K (Kn=20.95 to 0.12) for zirconium. The measurement on copper was carried out as a benchmark as the copper atomic beam has been reported to behave as an ideal monatomic gas due to the absence of any low-lying metastable states of copper. However, the velocity of the copper atomic beam was found to be much higher than that reported earlier. This is explained on the basis of electron impact excitation. For the atomic beam of zirconium, which has two low-lying metastable states, it was observed that the measured velocities approached the maximum velocity due to adiabatic free expansion, but could not attain it. This implicates only partial contributions to the atomic beam velocity from both thermal as well as electron impact excitation as the atom density of zirconium was not high enough even at the highest applied electron beam power.

When a high-intensity (∼ 250 mA/cm2), high-energy (∼ 48 kV) electron-beam (∼ 85 kW) produces zirconium vapor in an evacuated vessel, zirconium plasma is formed in the free space above the evaporating source. The plasma is produced by electron-impact ionization of the evaporated atoms and expands with the vapor. It is weakly ionized (∼ 0.1% degree of ionization) and has low electron temperature (∼ 0.3 eV). In applications like laser based isotope separation and purification of alloys, this electron-beam generated continuous plasma interferes detrimentally with the laser produced pulsed photoplasma which is pure. Hence there is a need to remove the plasma before it flows to the photoplasma region. In this paper we describe the studies on extraction of zirconium plasma by electrostatic field in parallel-pate geometry. It was observed that with increase of electron-beam current, the extractor plates were charged by the scattered electrons. This resulted in development of a negative voltage across the plates. ...

Laboratory spectra covering the nu7 band of ethane (C2H6) have been recorded, and measurements of integrated intensities of selected Q branches from these spectra are reported. The method by which the spectra were obtained is described, and a typical spectrum covering the PQ3 branch at 2976.8/cm is shown along with a plot of equivalent width vs. optical density for this branch. The values of the integrated intensities reported for each branch are the means of five different optical densities.

A finite-sized barium (Ba) photoplasma is generated through a two-step resonant photoionization method by shining laser pulses onto an atomic beam of Ba. The photoionization yield is estimated from the ratio of photoion density to neutral atom density measured in the laser–atom interaction region. The neutral atom density in the atomic beam is measured by an optical absorption technique where a Ba hollow cathode lamp (Ba-HCL) is used as an emission source. Since the photoplasma has a finite volume and it is pulsed in nature, the photoion density in the photoplasma is estimated through the collection of charge from the photoplasma. The measured ionization yield is compared with the calculated value that is obtained from an in-house developed code. It is observed that the values are in good agreement.

Atomic beams can easily be produced by allowing atoms to effuse through a channel. In an earlier investigation [A. Majumder et al., Vacuum 83, 989 (2009)], we had designed, fabricated, and characterized an effusive metal-vapor source using collinear-array of multi-channel. In this note, we describe the theoretical basis of designing the source. Atom density in atomic beam has been estimated using a set of analytical expressions for long-channel operated in transparent mode. Parametric studies on aspect ratio of channel, inter-channel separation, beam width, and vertical distance from the source are carried out. They are useful in providing physical picture and optimizing design parameters.

Electron beam is preferably used for large scale evaporation of refractory materials. Material evaporation from a long and narrow source providing a well collimated wedge shaped atomic beam has applications in isotopic purification of metals relevant to nuclear industry. The electron beam from an electron gun with strip type filament provides a linear heating source. However, the high power density of the electron beam can lead to turbulence of the melt pool and undesirable splashing of molten metal. For obtaining quiet surface evaporation, the linear electron beam is generally scanned along its length. To further reduce the power density to maintain quiet evaporation the width of the vapour source can be controlled by rotating the electron gun on its plane, thereby scanning an inclined beam over the molten pool. The rotation of gun has further advantages. When multiple strip type electron guns are used for scaling up evaporation length, a dark zone appears between two beams due to physical separation of adjacent guns. This dark zone can be reduced by rotating the gun and thereby bringing two adjacent beams closer. The paper presented here provides the simulation results of the electron beam trajectory and incident power density originating from two strip electron guns by using in-house developed code. The effect of electron gun rotation on the electron beam trajectory and power density is studied. The simulation result is experimentally verified with the image of molten pool and heat affected zone taken after experiment. This technique can be gainfully utilized in controlling the time averaged power density of the electron beam and obtaining quiet evaporation from the metal molten pool.

Transport of a low-current-density electron beam is simulated for an electrostatic accelerator system. Representative charged particles are uniformly assigned for emission from a circular indirectly-heated cathode of an axial electron gun. The beam is accelerated stepwise up to energy of 1 MeV electrostatically in a length-span of ~3 m using multiple accelerating electrodes in a column of ten tubes. The simulation is done under relativistic condition and the effect of the magnetic field induced by the cathode-heating filament current is taken into account. The beam diameter is tracked at different axial locations for various settings of the electrode potentials. Attempts have been made to examine and explain data on beam transport efficiency obtained from experimental observations.

Electron beam assisted physical vapour deposition (EB-PVD) and purification of metal by repeated melting using electron guns is a well-established technique in industrial metallurgy. Strip electron gun is considered a cost effective alternative to multiple pencil guns for handling of large size substrates. In the electron guns, the thermionic emission of the electrons from a filament is achieved by using AC or DC filament heating. A study of their relative merits and demerits was conducted for the both types of electron guns. Due to finite length of the filament, the magnetic field generated around the filament by heating current drops down towards ends. The DC filament heating results in electron beam with a comet shape having high power density hot spot at one end with low power density tails. With AC filament heating, electron beam oscillates with the frequency as that of heating current. The study of vapour flux distribution using DC gun revealed that highly directional vapour evolution takes place from a smaller hot spot whereas with AC gun vapour evolution occurs from an oscillatory 2D-evaporating source. The vapour deposit on substrate indicated that evaporation using DC gun caused splashing and granular deposit due to volumetric melting and evaporation from the ingot. This is contrary to the AC filament heating wherein quiet evaporation was observed due to surface melting and evaporation. The experimental results are critically reviewed to decide the configuration of electron guns for large-scale evaporation.

In an evaporator, when a high-energy continuous electron beam impinges a copper target, it generates an atomic beam. It is observed that plasma is formed. The primary and the backscattered electrons from the surface of the target produce copper plasma by electron-impact ionization of the atoms. The plasma is of low temperature, weakly ionized and is present in a weak transverse magnetic field. The magnetic field is used to bend the electrons from the gun. The plasma flows in a direction that is perpendicular to the target surface and transverse to the magnetic field. The plasma expansion is weakly collisional. It decays along the flow direction due to cross-field diffusion.

A high-resolution diode laser spectrum of the 882-cm−1 band of s-tetrazine has been obtained. A complete rotational analysis of this band, incorporating quartic and sextic centrifugal distortion coefficients, has been carried out. The rotational constants A, B, and C have been determined with an accuracy better than 10−5 cm−1. The analysis has shown the band to be A-type and, on this basis, the vibrational assignment of this band has been revised from ν12 to ν14.

High-resolution diode laser spectra and medium-resolution F-T spectra of deuterated ammonia have been obtained in the 700- to 1030-cm−1 region. Out of about 800 lines measured by diode laser spectroscopy, approximately 500 lines have been assigned to the ν2 transitions of NH2D. The parameters for the ground and ν2 states of NH2D have been derived by the simultaneous analysis of the infrared and microwave data. The standard deviation for the IR data is ∼8 × 10−4 cm−1. It is shown that the energy levels of NH2D in the ν2 state are heavily perturbed by inversion-rotation interaction and that it is necessary to include higher order inversion-rotation interaction terms to obtain a satisfactory fit of the observed data.

Absolute line intensities have been determined at room temperature for a total of 22 transitions belonging to rP and pP subbands in the ν6(E) perpendicular band of 12CH3D between 1062 and 1114 cm−1 under Doppler-limited resolution using a tunable diode-laser spectrometer system. Although the line intensities were determined with good precision (≈3%), the squared vibrational transition dipole matrix element derived from each line intensity showed large variations (≈500%) indicating intensity perturbations, possibly caused by Coriolis interactions between the ν3, ν5, and ν6 fundamentals. The “Herman-Wallis” F-factor coefficients derived from the rP and pP subband transitions were significantly different from each other, but compared well with those reported in a recent study by M. Delaveau (Ph.D. thesis, Universite de Paris-Sud, Orsay, 1985) using a Fourier transform spectrometer. Room temperature air- and nitrogen-broadened halfwidths have also been determined for 24 lines. The average of the ratios of nitrogen- to air-broadened halfwidths was 1.01 with a standard deviation of 0.01, giving almost equal broadening efficiencies for nitrogen and air. Room temperature self-broadened halfwidths were derived for two transitions with a mean value of 0.081 ± 0.001 cm−1 atm−1 at 296 K.

Absolute line intensities for several individual vibration-rotation transitions in the ν 2 bands of HDO and D 2 O have been determined at room temperature from laboratory spectra recorded with a tunable diode laser spectrometer. Two tunable semiconductor diode lasers operating in the 1250- to 1350- and 1060- to 1140-cm −1 spectral regions have been used in the recording of the data. Comparisons are made with previously published results where appropriate.

The vibration-rotation spectrum of the ν6 fundamental band of carbonyl fluoride (COF2) has been recorded at room temperature and 0.005 cm−1 resolution, using a Fourier transform spectrometer. Although the strong Q branch at 774 cm−1 is only partially resolved in the spectrum, most of the K structure of various J subgroups in the P and R branches has been fully resolved. More than 1500 transitions belonging to J values up to 40 have been assigned and simultaneously fitted with the microwave frequencies reported by J. H. Carpenter [J. Mol. Spectrosc. 50, 182–201 (1974)] with a standard deviation of 0.0006 cm−1. By incorporating quartic and sextic centrifugal distortion coefficients in Watson's reduced Hamiltonian in the Ir representation, upper state rotational constants A, B, and C have been determined to an accuracy better than 10−5 cm−1. Ground state rotational and fourth order centrifugal distortion constants were constrained in the analysis to the values reported by W. Lewis-Bevan et al. [J. Mol. Spectrosc. 113, 458–471 (1985)].

Air- and nitrogen-broadened half-widths and line shifts at room temperature for more than 60 individual vibration-rotation transitions in the nu1 fundamental band of (O-16)3 and several transitions in the nu3 band were determined from infrared absorption spectra. These spectra were recorded at 0.005/cm resolution with a Fourier-transform spectrometer. A tunable-diode-laser spectrometer operating in the 1090-1150/cm region was also used to record data on oxygen-, nitrogen-, and air-broadened half-widths for selected individual transitions. The nitrogen- and air-broadened half-widths determined by these two different measurement techniques are consistent to within 4 percent. The results are in good agreement with other published measurements and calculations.

Absolute intensities and self-, air- and N2-broadened half-widths have been determined for the first time for individual lines in the nu3(A1) band of (C-12)H3D near 7.6 microns from measurements of individual vibration-rotation lines using a tunable diode laser spectrometer. The intensity measurements are believed to be accurate to within three percent. Within experimental uncertainties, equal broadening efficiencies are found for both air and nitrogen. Self-broadened half-widths determined for three transitions yield an average half-width value of 0.803 + or -0.0010/cm/atm at 296 K.