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.     

An PBЕ-73C vacuum spark gap with a control circuit based on an inductive energy storage

The design and operating principle of a small (50 mm in diameter and 100 mm in height) РВЕ-73C vacuum spark gap are described. It is shown that it can be efficiently switched using a control circuit with a low (∼900 V) supply voltage, which is based on an inductive energy storage and a diode opening switch that forms a high-voltage igniting pulse with a rise time of nanosecond duration. The РВЕ-73C switching process is investigated at different rise times of igniting voltage pulses and different igniting current amplitudes. The results of tests of the spark gap operating in regimes of switching current pulses with an amplitude of 12 kA and a rise time of 800 ns are presented.     

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.     

High-frequency pulse generators based on SOS diodes with subnanosecond current cutoff time

Compact high-voltage generators with a pulse power of 100–500 MW, an output voltage of 150–400 kV, a pulse duration of 3–6 ns, and pulse repetition rates of 300–400 Hz and up to 5 kHz in a steady-state and a 30-s-long burst mode, respectively, are described. The output power-amplification unit is based on an inductive storage and SOS diodes with subnanosecond current cutoff time. Physical processes in the semiconductor structure of a SOS diode operating in the subnanosecond current cutoff mode are considered. The generator circuit designs and their test results are presented.     

The amplitude and current pulse duration of a supershort avalanche electron beam in air at atmospheric pressure

The results of experimental studies of the parameters (amplitude and duration) of a supershort avalanche electron beam (SAEB) generated in air at atmospheric pressure are presented. It is shown that the pulse duration of the beam current behind the foil from the entire area of the anode foil is larger than from small areas and depends on the cathode design. The number of electrons that are detected behind the 10-μm-thick Al foil is ∼6 × 10¹⁰ electrons, which corresponds to a SAEB amplitude of ∼100 A at a FWHM of the current pulse of ∼100 ps. An X-ray exposure dose per pulse of ∼1.8 mR was obtained using a 20-μm-thick copper foil. It was confirmed that the FWHM of a SAEB pulse is within ∼50 ps from small foil areas (with diameters of ∼7 mm or smaller).     

Formation of a 1.3-MV voltage pulse across a 13-Ω load with the help of the model BMΓ-160 magnetocumulative generator

An energy source designed on the basis of a BMΓ-160 magnetocumulative generator with transformer output, which enables one to form high-power (>100 GW) pulses with a current rise time of ∼1 μs across a 10-Ω load is described. Test results are provided for the generator with a load in the form of a liquid resistor connected to the source through two series gas-filled discharge switches with a trigger level of 300–350 kV each. A voltage pulse of 1.3 MV was obtained across a resistive load of 13 Ω by means of electric explosion of the conductors. Experimental pulse parameters correspond to theoretical data. Numerical simulation indicates that voltage pulses with magnitudes >1 MV and a rise time of ∼100 ns can be formed across a resistance of 13 Ω.     

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.     

An efficient cathode for generating an supershort avalanche electron beam in air at atmospheric pressure

The cathodes of accelerators intended for generating an ultrashort electron beam in air at atmospheric pressure were studied. A cathode allowing an increase in the amplitude of the beam current behind the foil by several times has been developed. The beam current amplitude obtained at a half-height pulse duration of ∼100 ps is ∼80 A.     

A plasma generator based on nonself-sustained low-pressure glow discharge with a large-volume hollow cathode

The results of studying nonself-sustained glow discharges in an electrode system with a hollow cathode with a volume of 0.25 m³ are presented. A high-current (up to 35 A) nonself-sustained glow discharge at low pressures (0.3–1.0 Pa) is initiated and sustained with the help of an auxiliary cold-hollow-cathode arc discharge. When the current of a nonself-sustained glow discharge increases from 2 to 35 A, its burning voltage changes from 40 to 300 V. These values are much lower than the voltage for a self-sustained glow discharge in the same electrode system. At a discharge current of 30 A, the electron concentration at the center of the hollow cathode is n _e ∼ 10¹⁰–10¹¹ cm⁻³ and the electron temperature is T _e ≈ 2 eV. The discharge considered can be used in the system for modification of materials and products.     

A compact subnanosecond high-voltage bipolar pulse generator with spark gaps

Two modifications of the compact subnanosecond high-voltage bipolar pulse generator with an active unit based on a high-impedance charging line, forming line, and two uncontrolled nitrogen spark gaps without gas purging are studied. In both cases, the forming lines are charged with compression of the energies of incident pulses with a ∼160-kV amplitude, a ∼4-ns duration, and a ∼1.5-ns leading edge. The difference of operation modes of the circuits and their efficiency are specified by a point of connecting the load. In conditions of nanosecond prebreakdown overvoltage at a 100-Hz repetition rate, the spark gaps were energized with a relative scatter of ±(100–170) ps, thus specifying the stability of the shape of output bipolar pulses with a voltage difference up to 250 kV.     

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.     

A SOS-Generator for technological applications

A solid-state nanosecond SOS-generator for electrophysical technology applications is described. In the input part of the generator, the energy arrives at the high-voltage magnetic compressor through IGBT modules and a step-up pulse transformer. The input part of the generator is equipped with an unused energy recuperation circuit, and, when the output pulse is formed, the microsecond pumping mode of the semiconductor opening switch (SOS) is realized. As a result, the complete efficiency of the generator operating into a matched load is increased from ∼40 to 60–62%. The other characteristics of the generator are as follows: the peak voltage is up to 60 kV, the current is up to 6 kA, the pulse duration is about 40 ns, the pulse repetition rate in the continuous mode is 1 kHz, and the average output power is up to 9 kW.     

A nanosecond light source for scintillation-and Cerenkov-detector calibration

A nanosecond blue-light source with increased brightness is described. A light-emitting diode by NICHIA is used. The pulse shaper triggering the light-emitting diode is based on avalanche transistors. The number of photons per pulse is ∼10⁹ at a light-pulse duration of ∼2 ns.     

A gas-ion source with a grid-stabilized plasma cathode

A two-stage source of a broad beam of gas ions is described. The source contains a grid-stabilized plasma cathode and an anode stage with a multicusp magnetic field. The emission current of the plasma cathode (which is based on a glow discharge with a hollow cathode) is controlled between 0.1 and 1 A. The voltage that is applied to a bipolar diode between its cathode grid and anode plasma and determines the energy of fast electrons ranges from 50 to 200 V. The operating pressure of the argon in the anode stage is 4 × 10^–3–1 × 10^–1 Pa. A beam of argon ions having an energy of up to 5 keV and a current of >100 mA is formed by a two-electrode ion-optical system with a working area of 50 cm².__________Translated from Pribory i Tekhnika Eksperimenta, No. 2, 2005, pp. 107–111.Original Russian Text Copyright © 2005 by Gavrilov, Kamenetskikh.     

A source of gas, vapor, metal, and carbon ions based on a low-pressure hollow-cathode discharge

A compact source of gas, vapor, metal, and carbon ions based on a cold-hollow-cathode reflective discharge has been developed, in which a 6-mm-diameter flat target (Cu, Mo, W, C) is installed on the bottom of the cold cathode insulated from it. The density of the ion flow from cathode plasma reaches 100 mA/cm² at an accelerating voltage of up to 10 kV and a discharge current of 0.2-0.5 A. Vapors produced during ion sputtering of the target are ionized in the cathode and anode cavities. A beam containing ions of the plasma-producing gas and vapor is extracted throug h the channel in the reflector cathode. A fraction of the vapor of the sputtered target, the flow of which is sufficient for growing layers at a rate of ∼0.03 nm/s at a distance of 10 cm from the emission channel under the action of an ion beam, is extracted together with ions. The fraction of metal ions in the extracted beam is 0.05-0.10. The total current of the ion beam is 20-30 mA.     

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.     

A 3He cryostat inserted into a refrigerator with an impulse tube

A compact autonomous ³He cryostat inserted into a two-stage refrigerator with an impulse tube is described. The cryostat contains baths filled with ⁴He and ³He and evacuated with cryosorbers to temperatures of ∼1 and ∼0.35 K, respectively. The low temperature is maintained for 6–8 h at an amount of liquid ³He filling the cryostat of ∼0.035 mol. The dimensions of the insert (below the upper flange) are 49 mm (diameter) and 720 mm (length). The insert is introduced into a hermetically sealed tube-well filled with a heat-exchange gas during operation, which promotes the heat removal to levels of 45–50 K (the first stage of the impulse tube) and 3–4 K (the second stage of the impulse tube). The cryostat can be mounted in and extracted from both the warm cryostat and the cryostat cooled to low temperatures.     

Plasma sources of ions of solids

Three variants of the design of ion sources are described: (1) with a hollow cathode and an anode-evaporator system in the rear part of the source, (2) with a cylindrical anode, and (3) with a hollow cathode and an anode in the front part. It is shown that these sources are most suitable for obtaining ion beams of solid-state elements and provide ion currents of ∼70–100 μA (for Al, Bi, As, Sb), 25 μA (Eu), and 15–30 μA (Fe, V, Cr, and doubly charged and molecular ions). Such sources are characterized by a relatively long operation time (tens of hours) and a low energy consumption level (300–400 W). The operational principle of ion sources is described with consideration for the differences in their designs. The experimental results are presented: the dependences of the ion currents on the discharge current, cathode current, and induction of the magnetic field of the source’s electromagnet, as well as the results of the computer simulations that are based on a numerical model of the ionization of atoms in the source.     

A new method for charged particles identification with a CsI(Tl) crystal

A spectrometer for detecting and identifying light charged particles with low energies (>∼1 MeV) is described. The spectrometer consists of a thin CsI(Tl) crystal, an ФЭУ-176 photomultiplier, and a waveform digitizer. Digital oscillograms of anode pulses are stored and analyzed in off-line processing. In order to reconstruct the energy and specific energy losses, the two-component character of the scintillation fluorescence decay in a CsI(Tl) crystal and the dependence of the fast component on the specific loss value are used. A digital particle identification method is proposed. The results of experimental studies of the CsI(Tl) crystal scintillation properties and efficiency in identifying electrons, protons, and α-particles in an energy range of ∼1–10 MeV are presented. It is shown that the efficiency of the digital method for proton and α-particle identification is 1.5–2 times higher than that of the known analog methods.     

A 400-keV X-ray generator with the pulse duration variable within 10–80 ns and an up to 70-Gy radiation dose

A high-power X-ray generator is created based on a universal setup for the experimental development of components of electrophysical installations (spark gaps, insulators, liquid resistors, etc.). The maximum energy of X-ray quanta is 400 keV, the pulse duration can be varied in steps from 10 to 80 ns, the radiation dose in the atmosphere near the exit window is ∼70 Gy, and the X-ray pulse is synchronized within ±15 ns with respect to the external trigger pulse. The key units of the setup are a shielded 600-kV Marx generator with a high-precision switching and a low-impedance high-voltage pulse former with a single or double coaxial line. The electric length of the lines can be increased by extending its body and conductors and by filling it with transformer oil, glycerin, or water. A design of the diode with a ∼70-kA radially converging ring electron beam and sidewall X-ray radiation release to the atmosphere through a thin dielectric window is presented. The dose characteristics and spectrum of the X-ray radiation are given.