A forevacuum pulse arc-discharge-based plasma electron source

An arc-discharge-based electron source is described, which is designed for forming a pulsed wideaperture electron beam in the forevacuum pressure range (4–15 Pa). At an accelerating voltage of 12 kV, a current of 80 A was extracted from the emitting surface with an area of 80 cm² in the submillisecond range of pulse durations. The current density distribution over the beam cross section is close to a Gaussian function, and the surface-averaged beam energy density in a pulse reached 10 J/cm².     

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.     

A source of a high-power relativistic electron beam with high brightness

A ribbon diode of a U-2 accelerator (800 kV, ∼30 kA) intended for generating a high-intensity electron beam for heating plasma in a GOL-3 multimirror magnetic trap (Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences) is described. The parameters of the beam characterized by a high brightness (∼7 kA/(cm² sr)) in a magnetic field of ∼5 T resulting from a numerical simulation of the beam formation process are presented. The results of simulation of the beam transport and transformation of the profile of its cross section during movement of electrons in a curvilinear guiding magnetic field are presented. The calculated cross section is compared to the beam imprint on a target.     

Measuring the mechanical recoil impulse of a polymeric target upon impact of a high power electron beam

A method for measuring the mechanical recoil impulse of a target produced by the relativistic electron beam of the Calamary accelerator is described. A detector based on a piezoelectric sensor is used in measurements. Results of measurements are presented for the mechanical recoil impulse produced by the relativistic electron beam with an energy as high as 300 keV, a current of up to 30 kA, and a duration of ~100 ns that is incident on an epoxy target. The energy flux density on the target surface is varied in the range of 1–10 GW/cm². The maximum measured impulse value is 0.32 N · s at an energy flux density of 10 GW/cm² (an energy fluence of 810 J/cm2).     

AУPT-1M accelerator for radiation technologies

AУPT-1M modernized electron accelerator with an accelerating voltage up to 1 MV, a 1-kW electron beam power, and a 100-ns pulse duration is described. As compared to the prototype (УPT-1 accelerator), the layout of assemblies is changed in it, allowing one to place it in rooms with heights up to 2.5 m. It uses Murata capacitors and a ТQPи1–10k/75 thyratron with a cold cathode for switching. The computer-aided parameter-monitoring system is created. A metal-ceramic cathode consisting of several elements with ～15% nonuniform current density distribution of the electron beam on the exit foil was used to obtain an electron beam with a width of up to 400 mm. The accelerator can be used in radiation technologies in layers with a thickness of up to 0.3 g/cm².     

A Matrix Carbon Detector for Measuring the Energy Flux of a High-Power Beam of Hydrogen Ions

A matrix detector consisting of small calorimeters based on УПВ-1 pyrolytic carbon is described. The detector allows measurements of the spatial distribution of the energy flux of a high-power hydrogen ion beam to be taken over its cross section. Each calorimeter occupies an area of 4 cm², and the area of its working body is 0.25 cm². An unambiguous relation between the heat flux value, the irradiation time, and the calorimeter temperature is established by calculations. The calorimeter measurement error was estimated at ～4%, and the spread of the sensitivity coefficients between the calorimeters was 5–6% (1σ). The detector was used to measure the distribution of the energy flux of hydrogen ions over the cross section of the “scanned” beam 10 cm in diameter from a high-current accelerator of the НГ-12И facility.     

YPT-0.5 repetitive-pulse nanosecond electron accelerator

An YPT-0.5 repetive-pulse nanosecond electron accelerator designed according to the thyratron-pulse transformer-semiconductor opening switch scheme is described. Its accelerating voltage reaches 0.5 MV, the FWHM pulse duration is 50 ns, and the pulse repetition rate is 200 Hz. A metal-dielectric cathode allows for obtaining an electron beam with a diameter of 30–100 mm at a maximum pulse current density of 40 A/cm². Operating in the bremsstrahlung generator mode, the accelerator provides an absorbed dose rate of 30.4 Gy/min at a distance of 5 cm from the target.     

Thermal imaging diagnostics of powerful ion beams

Thermal imaging diagnostics of the total energy of a pulsed ion beam and energy-density distribution over the cross section is described. The diagnostics was tested on the TEMП-4M accelerator in the conditions of formation of two pulses: (i) the first plasma-forming pulse is negative (300–500 ns, 100–150 kV) and (ii) the second generated one is positive (150 ns, 250–300 kV). The beam composition includes carbon ions (85%) and protons, and the power density is 0.2–3.0 J/cm² (for various diodes). The diagnostics was applied in studies of the powerful ion beam, formed by an ion diode with self insulation (two-pulse mode) and external magnetic insulation in the single-pulse mode. The diagnostics was intended to measure the beam energy density in a range of 0.05–5.00 J/cm² in the absence of erosion and ablation processes on the target. When an infrared camera with a 140 × 160-pixel matrix is used, the spatial resolution is 0.9 mm. The measurement time does not exceed 0.1 s.     

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.     

Evaluation of the effective cross‐sections for recombination and trapping in the case of pure spinel

In this paper, we have investigated the evolution of the secondary electron emission in the case of pure spinel during electron irradiation, achieved in a scanning electron microscope at room temperature, which is derived from the measurement of the induced and the secondary electron currents. It was observed from the experimental results, that there are two regimes during the charging process: a plateau followed by a linear variation, which are better identified by plotting the logarithm of the secondary electron emission yield lnσ as function of the total surface density of trapped charges in the material Q_T. For positive charging, E₀ = 1.1 and 5 keV, the slope of the linear part, whose value is of about 10^?10 cm² charge^?1, is independent of the primary electron energy. It is interpreted as a microscopic cross section for electron–hole recombination. For negative charging of pure spinel, E₀ = 15 and 30 keV, the slope is associated with an electron trapping cross section close to 10^?14 cm² charge^?1, which can be assigned to the microscopic cross section for electron trapping. This trapping cross section is four orders of magnitude lower than the recombination one.     

Investigation of the homogeneity of a high-power ion beam formed by a diode with a closed electron drift

The results of an investigation of the energy-density distribution over the cross section of a pulsed ion beam formed with a passive-anode diode in the mode of magnetic insulation and a closed electron drift in the anode–cathode gap are presented. Diodes of two types are studied: with external magnetic insulation (B_r diode) on the BIPPAB-450 accelerator (400 kV, 80 ns) and self-magnetic insulation of electrons (spiral diode) on the TEMP-4M accelerator (250 kV, 120 ns). In the investigated diodes, various processes are used to form anode plasma: a breakdown over the surface of a dielectric coating on the anode and ionization of the anode surface with accelerated electrons (B_r diode), as well as explosive emission of electrons (spiral diode). To analyze the ion-beam energy density, thermal-imaging diagnostics is used with a spatial resolution of 1–2 mm. The energy-density is calculated from the one-dimensional Child–Langmuir relationship. It is shown that a continuous plasma layer is efficiently formed on the working anode surface for all the investigated diodes. The anode-plasma concentration is rather high, and the beam-energy density is limited by the space charge of ions, but not by the plasma concentration. It is found that, when the magnetic field in the Br-diode anode–cathode gap decreases or the electron current in the spiral diode increases, the energy density of the high-power ion beam rises significantly, but the beam homogeneity decreases.     

Upgrade of the beam profile ionization monitor for the KOMBAS fragment separator

The results from upgrade of an ionization beam profile monitor (IBPM) are presented. The IBPM consists of a conventional capacitor that extracts the ionization products of the residual gas and analyzing capacitors. The main objective of this upgrade was to create a device with uniform spatial resolution. For this purpose, an additional difference of potentials, the ramping of which allows the beam cross section to be scanned, is applied between the capacitors of the monitor, while the electric fields in the capacitors themselves remain constant. Two IBPMs have been developed as a result of the facilitys upgrade: an IBPM for on-line monitoring of the vertical and horizontal beam current distributions in the beam line in an area of 8 × 8 cm² with a uniform 1-mm resolution, and an IBMP for detailed beam profile monitoring with a uniform resolution of 1 × 1 mm² over the scanning region. It was established experimentally that the proposed scanning technique provides good results in beam profile measurements when the ion component of the ionized residual gas is extracted; for the electron component, the result is much worse.__________Translated from Pribory i Tekhnika Eksperimenta, No. 2, 2005, pp. 61–66.Original Russian Text Copyright © 2005 by Teterev, Phi Thanh Huong.     

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.     

Measurements of the profile of an intense electron beam

Methods for measuring the profiles of high-power electron beams by using a thin tungsten wire moved transversely to the beam have been developed. In one method, the electron current intercepted by the wire is measured and the beam profile is determined from a solution to the Abel equation under the assumption of axial beam symmetry. The second method is based on the detection of the local radiation emitted by the wire being heated by the beam to 1700–2200 K. The wire is additionally heated by an electric current in order to improve the sensitivity and spatial resolution. The measured beam current density is ～5–50 A/cm², and the resolution is ～0.1 cm.     

A study of the time and amplitude characteristics of the scintillation counter two meters long with ΦЭУ-115M photomultiplier tubes

The time and amplitude characteristics of a scintillation counter were investigated on an accelerator beam with a momentum of 5 GeV/c at the Institute for High Energy Physics. The scintillator, with a length of 2 m and a cross section of 2.5 × 2.5 cm², was viewed from its end faces by ΦЭУ-115M photomultiplier tubes (PMTs). The dependences of the signal amplitude and the time resolution of a PMT on the position of a particle track along the scintillator were described by quadratic exponentials. When a constant fraction discriminator was used to form the PMT signal, the time resolutions at the center and at the periphery of the counter were 150 and 80 ps, respectively. Better results were obtained with a standard leading-edge discriminator after correcting the dependence of its response time on the signal amplitude.     

An arc generator of a broad plasma stream

The design and basic parameters of an arc plasma generator based on a combined cathode are described. The cathode consists of a hot tungsten filament located in the hollow cathode. A plasma stream with a cross section of 150×10 cm² and a density of ∼10¹⁰ cm⁻³ at a pressure of 0.1–1 Pa is generated at a discharge current of up to 60 A without a cathode spot. The plasma generator can be utilized for final cleaning and activation of surfaces of materials and articles before depositing functional coatings on them and in plasma-assisted deposition by using either vacuum arc or magnetron discharges.     

Effect of the sample annealing temperature and sample crystallographic orientation on the charge kinetics of MgO single crystals subjected to keV electron irradiation

This paper focuses on the effect of sample annealing temperature and crystallographic orientation on the secondary electron yield of MgO during charging by a defocused electron beam irradiation. The experimental results show that there are two regimes during the charging process that are better identified by plotting the logarithm of the secondary electron emission yield, lnσ , as function of the total trapped charge in the material Q_T. The impact of the annealing temperature and crystallographic orientation on the evolution of lnσ is presented here. The slope of the asymptotic regime of the curve lnσ as function of Q_T, expressed in cm² per trapped charge, is probably linked to the elementary cross section of electron–hole recombination, σ_hole, which controls the trapping evolution in the reach of the stationary flow regime.     

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 monitor for heavy ion flux density control based on detection of recoil protons during irradiation of polymer films

An monitor for control of accelerated particle flux density used in irradiation of polymer films with heavy ions with a low track density (10³?5 × 10⁷ cm^?2) is based on detection of recoil protons. It has been designed to control irradiation of a film with a width of up to 650 mm and is composed of five PIN diodes with a hydrogenous target placed in front of each diode. The sensitivity of the monitor with a polyethylene target to the density of a xenon ion beam is described by a linear function; its value is (4.0±0.5) × 10^?3 pulses/(ion/cm²). The instrument is capable of monitoring ion flux densities of <10⁶ cm^?2, for which all other methods are ineffective. It can be used to determine the track density in a finished product, bypassing the stage of a check with an electron microscope. The signals from the monitor can also be used to introduce a feedback in a system of automatic beam tuning in order to improve the film irradiation quality. The radiation hardness of silicon detectors is ≈ 10¹² protons/cm². At an average detector load of ≈ 10⁴ protons/cm², the average service life of the monitor is 10⁸ s of continuous operation.     

Ionization Profilometer of the Beam Position on the Target of the COMBAS Fragment-Separator

The operation principle of a newly designed ionization profilometer is described, and results of its tests with a 30-MeV/nucleon ⁴⁰Ar ion beam are presented. The measured beam density distribution over its cross section is given. The space resolution of this profilometer is 1 × 1 mm. The image of this beam on a fluorescent screen is shown for comparison. It is determined that the minimum value of the beam current at which it is still possible to measure its profile is 3 nA. The measurements were performed at residual gas pressures of 2 × 10^–3 and 7 × 10^–3 Pa.