Generation of a pulsed high-current low-energy beam in a plasma electron source with a self-heated cathode

The transition of a low-current discharge with a self-heated hollow cathode to a high-current discharge is studied, and stability conditions for the latter in the pulsed–periodic mode with a current of 0.1–1.0 kA, pulse width of 0.1–1.0 ms, and a pulse repetition rate of 0.1–1.0 kHz are determined. The thermal conditions of the hollow cathode are analyzed, and the conclusion is drawn that the emission current high density is due to pulsed self-heating of the cathode’s surface layer. Conditions for stable emission from a plasma cathode with a grid acting as a plasma boundary using such a discharge are found at low accelerating voltage (100–200 eV) and a gas pressure of 0.1–0.4 Pa. The density of the ion current from a plasma generated by a pulsed beam with a current of 100 A is found to reach 0.1 A/cm². Probe diagnostics data for the emitting and beam plasmas in the electron source are presented, and a mechanism behind the instability of electron emission from the plasma is suggested on their basis.     

The performance of the series III 200kv high current industrial ion implanter

Two years of operation of the Series III Implanter have revealed the full potential of this machine.

The arsenic and phosphorus performance of this machine has greatly exceeded the initial 4 mA design criterion and 8 mA beams of these elements are readily obtainable. The boron beam currents are very dependent upon source history, but 1.2 mA is always available and 3 mA can be obtained from a well conditioned source.

The single gap post-acceleration system has proved very successful, a particular advantage over multi-gap tubes being the 100% beam transmission for any post-acceleration voltage and milliampere beams.

The processor system consists of a large capacity (54–3″. 27–4″, 18–5″ or 9–6″ silicon wafers) racetrack carousel which gives a mechanical scan free of geometric errors for wafers up to 61/2″ diameter. The wafers are mounted on plates with a clamping technique designed for use with an automatic loading system. The large implantation area (approximately 4,000 cm²) minimizes the temperature rise during implantation. The large beam area (approximately 25 cm² at the carousel) minimizes the pulse heating effect as the wafers sweep through the beam.     

Ultrashort electron beam and volume high-current discharge in air under the atmospheric pressure

Conditions are studied under which an electron beam and a volume discharge with a subnanosecond rise time of a voltage pulse are produced in air under atmospheric pressure. It is shown that the electron beam appears in a gas-filled diode at the front of the voltage pulse in ∼0.5 ns, has a half-intensity duration of ≤0.4 ns and an average electron energy of ∼0.6 of the voltage across the gas-filled diode, and terminates when the voltage across the gap reaches its maximum value. The electron beam with an average electron energy of 60 to 80 keV and a current amplitude of ≥70 A is obtained. It is assumed that the electron beam is formed from electrons produced in the gap due to gas ionization by fast electrons when the intensity of the field between the front of the expanding plasma cloud and the anode reaches its critical value. A nanosecond volume discharge with a specific power input of ≥400 MW/cm³, a density of the discharge current at the anode of up to 3 kA/cm², and specific energy deposition of ∼1 J/cm³ over 3 to 5 ns is created.     

重复脉冲强流电子束源长时间稳定运行实验研究

 简要阐述了脉冲变压器型重复脉冲强流电子束加速器CHP01的组成、主要特点及工作原理，利用设计的重复脉冲强流电子束源进行了长时间运行实验研究，实验结果达到：在100 Hz重复频率下连续运行5 s，脉冲变压器能稳定输出电压1.15 MV,强流束二极管输出电压超过800 kV、束流7 kA、脉冲宽度45 ns，阴极电子发射密度超过10 kA/cm²，且运行稳定可靠。利用该电子束源进行了X波段类周期慢波结构微波器件实验研究，在50 Hz重复频率下连续运行5 s，输出微波功率超过1 GW，脉冲宽度大于25 ns。     

Generation and transport of high-current, low-energy electron beams in a system with a gas-filled diode

Investigations of the generation and transport of a high-current, low-energy electron beam are performed in a system with a gas-filled diode based on a plasma cathode. At accelerating voltages of up to 20 kV and pressures of (1–5)×10⁻¹ Pa, a beam with an emission current of 600 A, emission current density of 12 A/cm² and pulse duration of 30 μs if obtained in a diode with a grid-stabilized emission opening having a diameter equal to 8 cm. The beam is transported in the absence of an external magnetic field over a distance of 20 cm. The beam is compressed by its self-magnetic field, and the current density at the collector reaches 100 A/cm² when the beam diameter is 3 cm. Zh. Tekh. Fiz. 68, 44–48 (January 1998)     

Sensitive detection of acrolein and acrylonitrile with a pulsed quantum-cascade laser

We report on spectroscopic measurements of acrolein and acrylonitrile at atmospheric pressure using a pulsed distributed feedback quantum-cascade laser in combination with intra- and inter-pulse techniques and compare the results. The measurements were done in the frequency region around 957 cm^?1. In the inter-pulse technique, the laser is excited with short current pulses (5–10 ns), and the pulse amplitude is modulated with an external current ramp resulting in a ～2.3 cm^?1 frequency scan. In the intra-pulse technique, a linear frequency down-chirp during the pulse is used for sweeping across the absorption line. Long current pulses up to 500 ns were used for these measurements which resulted in a spectral window of ～2.2 cm^?1 during the down-chirp. These comparatively wide spectral windows facilitated the measurements of the relatively broad absorption lines (～1 cm^?1) of acrolein and acrylonitrile. The use of a room-temperature mercury-cadmium-telluride detector resulted in a completely cryogen-free spectrometer. We demonstrate ppb level detection limits within a data acquisition time of ～10 s with these methodologies.     

Generation of superintense femtosecond pulses by the Cr:forsterite laser system

A repetitively pulsed chromium-forsterite laser system is created. High-power femtosecond light pulses are generated at the fundamental (1.24 μm) and second-harmonic (0.62 μm) wavelengths. Theoretical analysis is performed to optimize the output pulse energy. Laser pulses with a duration of 110 fs, an energy of 1 mJ, and a repetition rate of 1–50 Hz are generated. The intensity of the focused beam is greater than 10¹⁶ W/cm². High-efficiency radiation conversion into the second harmonic is used to increase the energy contrast of the generated pulses. Original Text ? Astro, Ltd., 2006.     

Physicomechanical properties of the surface of a zirconium alloy modified by a pulsed ion beam

The physicomechanical properties of the surface of the Zr-1% Nb zirconium alloy modified by a pulsed carbon ion beam with a pulse duration of 80 ns, an energy of 200 keV, and a current density of 120 A/cm² are studied at four regimes having different numbers of pulses. Irradiation by a carbon ion beam results in hardening of the surface layer to a depth of 2 μm, grain refinement to 0.15–0.8 μm, zirconium carbide formation, and a decrease in the hydrogen permeability of the zirconium alloy.     

Detection of accelerated particles from pulsed plasma discharge using solid state nuclear track detector

The ion beam of a Mather-type 23.25 J plasma focus device operated with air filling at 10 Torr was registered using CR-39 nuclear track detector. The irradiated samples were etched in NaOH solution at 70°C for 1 h. It is found here that plasm a beam contains multi-components of microbeams. The individual track density of microbeams is estimated and the total current density of the plasma stream is measured to be 1.2 mA/cm². A model for counting the track density of individual microbeams is proposed here. Faraday cup measurements showed the ion pulse with energy ranging from 5.8 keV to 3.3 keV.      

Erosion products of plasma facing materials formed under ITER-like transient load and deuterium retention in them

Erosion of the plasma-facing materials in particular evaporation of the materials in a fusion reactor under intense transient events is one of the problems of the ITER. The current experimental data are insufficient to predict the properties of the erosion products, a significant part of which will be formed during transient events (edge-localized modes (ELMs) and disruptions). The paper concerns the experimental investigation of the graphite and tungsten erosion products deposited under pulsed plasma load at the QSPA-T: heat load on the target was 2.6 MJ/m² with 0.5 ms pulse duration. The designed diagnostics for measuring the deposition rate made it possible to determine that the deposition of eroded material occurs during discharge, and the deposition rate is in the range (0.1–100) × 10¹⁹ at/(cm² s), which is much higher than that for stationary processes. It is found that the relative atomic concentrations D/C and D/(W + C) in the erosion products deposited during the pulse process are on the same level as for the stationary processes. An exposure of erosion products to photonic energy densities typical of those expected at mitigated disruptions in the ITER (pulse duration of 0.5–1 ms, integral energy density of radiation of 0.1–0.5 MJ/m2) significantly decreases the concentration of trapped deuterium.     

Effect of the electron beam and ion flux parameters on the rate of plasma nitriding of an austenitic stainless steel

The method of nitriding of metals in an electron beam plasma is used to change the current density and energy of nitrogen ions by varying the electron beam parameters (5–20 A, 60–500 eV). An electron beam is generated by an electron source based on a self-heated hollow cathode discharge. Stainless steel 12Kh18N10T is saturated by nitrogen at 500°C for 1 h. The microhardness is measured on transverse polished sections to obtain the dependences of the nitrided layer thickness on the ion current density (1.6–6.2 mA/cm²), the ion energy (100–300 eV), and the nitrogen-argon mixture pressure (1–10 Pa). The layer thickness decreases by 4–5 μm when the ion energy increases by 100 V and increases from 19 to 33 μm when the ion current density increases. The pressure dependence of the layer thickness has a maximum. These results are in conflict with the conclusions of the theory of the limitation of the layer thickness by ion sputtering, and the effective diffusion coefficient significantly exceeds the well-known reported data.     

Gbit/s rate bipolar pulse modulation of semiconductor injection lasers

Using a bipolar drive current pulse shape and very low threshold (9 mA) lasers, zero-background pseudorandom optical pulses were generated and detected at a rate of up to 4 Gbit/s without a pattern effect. The drive current pulse consists of a forward pulse followed by a reverse pulse, each of 70 ps duration and about 400 mA amplitude. No DC bias was applied, which is a necessary condition for pattern-effect-free modulation.     

Si homojunction structured near-infrared laser based on a phonon-assisted process

We fabricated several near-infrared Si laser devices (wavelength ～1300 nm) showing continuous-wave oscillation at room temperature by using a phonon-assisted process induced by dressed photons. Their optical resonators were formed of ridge waveguides with a width of 10 μm and a thickness of 2 μm, with two cleaved facets, and the resonator lengths were 250–1000 μm. The oscillation threshold currents of these Si lasers were 50–60 mA. From near-field and far-field images of the optical radiation pattern, we observed the high directivity which is characteristic of a laser beam. Typical values of the threshold current density for laser oscillation, the ratio of powers in the TE polarization and TM polarization during oscillation, the optical output power at a current of 60 mA, and the external differential quantum efficiency were 1.1–2.0 kA/cm², 8:1, 50 μW, and 1 %, respectively.     

Deposition of ultrahard Ti–Si–N coatings by pulsed high-current reactive magnetron sputtering

We report on the results of investigation of properties of ultrahard Ti–Si–N coatings deposited by pulsed high-current magnetron reactive sputtering (discharge pulse voltage is 300–900 V, discharge pulse current is up to 200 A, pulse duration is 10–100 μs, and pulse repetition rate is 20–2000 Hz). It is shown that for a short sputtering pulse (25 μs) and a high discharge current (160 A), the films exhibit high hardness (66 GPa), wear resistance, better adhesion, and a lower sliding friction coefficient. The reason is an enhancement of ion bombardment of the growing coating due to higher plasma density in the substrate region (10¹³ cm^–3) and a manifold increase in the degree of ionization of the plasma with increasing peak discharge current (mainly due to the material being sputtered).     

Characteristics of polymer velvet as field emitters under high-current pulsed discharge

In this paper we investigated the surface morphology and emission property of polymer velvet in a cathode test system powered by a ∼400 ns, ∼400 kV pulsed generator. After a series of pulse shots, the velvet surface exhibited an obvious decrease in the amount of emitters, namely, the smoothing of microprotrusions, indicating a lower field enhancement factor or a higher turn-on electric field than that for no shots. As the velvet cathode lifetime proceeded, the beam degradation was observed in terms of the voltage pulse length, maximum emission current, and rise time of diode current. Further, the average current density significantly decreased during a 100 pulse shot test, from 280 to 160 A/cm². The surface discharge caused many plasma spots on the velvet surface. The cathode plasma expands towards the anode, directly leading to the diode gap closure. The degradation in the velvet performance after high-current emission may be related to this behavior of cathode plasma. Finally, the electron emission mechanisms, how to affect the surface morphology of velvet, are presented.     

X射线探测器的脉冲标定技术

利用强流电子束技术产生通量密度为10¹⁸—10¹⁹X-ray photon/sr·s的脉冲CuKX射线源,标定PIN型硅二极管半导体探测器对X光子的脉冲灵敏度。用绝对X射线监测器——P10气体脉冲电离室作为脉冲X射线通量密度的标准。脉冲电荷自动测量仪由微处理机进行程序控制,并予以实时校准。该电离室测量通量密度的精度为±5％,适用的能通量率范围可达4×10^-9—2×10²W/cm²,适用的光子能量范围为1.5—10keV,标定探测器的精度为±7.0％,并发现PIN型硅二极管的脉冲灵敏度比稳态X射线束标定的灵敏度高30％左右。 关键词：     

Laser emission efficiency of semiconductor target of gas diode in the picosecond range

Laser radiation excited in a cadmiumsulfide semiconductor target (ST) (λ = 522 nm) by a high-intensity subnanosecond electron beam (EB) with an energy of 70–150 keV has a maximum intensity of 3 · 10⁷W/cm² at an efficiency of~10%. Lasing arose at the EB exciting pulse front. The laser radiation pulse shape reproduced the EB pulse shape.     

Designing and testing a compton converter of gamma radiation and x-rays to electric current

The design and testing of a Compton current generator are briefly described. Its current response to a γ quantum (i.e., sensitivity) is estimated at η=7.0×10⁻²¹ (A cm² s)/γ. At relatively high gamma fluxes, the generator can be employed as a battery charger. When it is fed by a pulsed gamma flux, the resulting current pulse is capable of triggering the equipment and evaporating a metal wire synchronously with the application of the gamma pulse. The generator can also be used as a direct-charge radiation detector for determining the dose and dose rate of a radiation pulse, as well as its shape.     

Dynamics of high-temperature plasma formation during laser irradiation of three-dimensionally structured,low-density matter

Results are presented from an experimental investigation of the properties of the plasma produced by the action of a radiation pulse at the second harmonic of a Nd laser, with average intensity ~5·10¹⁴ W/cm² in the focal spot, on flat targets consisting of porous polypropylene (CH)_x with an average density of 0.02 g/cm³ (close to the critical plasma density) and with ~50 μm pores. The properties of the laser plasma obtained with porous and continuous targets are substantially different. The main differences are volume absorption of the laser radiation in the porous material and much larger spatial scales of energy transfer. The experimentally measured longitudinal ablation velocity in the porous material was equal to (1.5–3)·10⁷ cm/s, which corresponds to a mass velocity of (3–6)·10⁵ g/cm²· s, and the transverse (with respect to the direction of the laser beam) propagation velocity of the thermal wave was equal to ~(1–2) ·10⁷ cm/s. The spatial dimensions of the plasma plume were ~20–30μm. The plasma was localized in a 200–400μm region inside the target. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 7, 462–467 (10 October 1996)     

Nichtstationäre Photoleitung in Anthrazen

Some pulsed photoconductivity experiments in pure Anthracene in the 250–400 nm region have been performed. According to earlier measurements the mobility of holes and electrons was found to be 0.85 cm²/Vsec±10% and 0.4 cm²/Vsec±10%. By delayed application of the electrical field after uv-flash-excitation the decay of carriers in the zone of generation near the crystal surface could be observed. Free holes decay approximately with 1/t but bimolecular recombination can not be the predominant recombination process. The time constant of the initial decay is 1.2–2 microseconds. An explanation of the decay curves was found by considering diffusion and surface recombination. The initial electron decay time is smaller than 0.7 microseconds. The electron-hole recombination coefficient was determined by injecting thin carrier sheets from both sides into the crystal and observing the decay of the pulse while the two sheets penetrate each other. A value of 3 · 10^?6 cm³/sec was found.