A Modernized PC-20 Facility for Studying the ... - Springer Link

Instruments and Experimental Techniques, Vol. 45, No. 2, 2002, pp. 248–255. Translated from Pribory i Tekhnika Eksperimenta, No. 2, 2002, pp. 112–119. Original Russian Text Copyright © 2002 by Barinov, Budkov, Dan’ko, Dolgachev, Kalinin, Karpov, Lobanov, Maslennikov, Khodeev.

GENERAL EXPERIMENTAL TECHNIQUES

A Modernized PC-20 Facility for Studying the Characteristics of a Plasma-Opening Switch N. U. Barinov,*† S. A. Budkov,* S. A. Dan’ko,* G. I. Dolgachev,* Yu. G. Kalinin,* V. E. Karpov,** A. I. Lobanov,** D. D. Maslennikov,* and I. A. Khodeev* * Russian Research Center Kurchatov Institute, pl. Kurchatova 1, Moscow, 123182 Russia ** Moscow Physicotechnical Institute, Institutskii proezd 9, Dolgoprudnyi, Moscow oblast, 141700 Russia Received July 31, 2001

Abstract-A modernized PC-20 facility with a plasma opening switch (POS) is described. It contains a fourmodule voltage pulse (Marx) generator (MXG) connected via a high-voltage feedthrough to a POS. The energy stored in the MXG is increased by a factor of 12.5 and amounts to 240 kJ at a maximum voltage of 1 MV. At such a voltage, the POS current amplitude is 320 kA and the current rise time is 2 µs. The breakdown strength of the high-voltage insulator is raised to a significant degree. The modernized facility was used in experiments in which the maximum accessible POS parameters (the obtained voltage, passed charge density, etc.) were evaluated. A voltage of up to 3.5 MV was obtained in the first experiments at a MXG voltage of 0.84 MV and a current of 300 kA.

INTRODUCTION Plasma-opening switches (POSs) are widely used in high-power pulse engineering as efficient and comparatively cheap power sharpeners. A generator based on a POS [1] is an LC circuit closed through the POS (Fig. 1). The POS is a section of a vacuum coaxial line, the electrodes of which are connected by a plasma jumper over a certain length. One end of the line is connected to a voltage pulse generator (MXG) based on a capacitive energy storage, and the other end of the line is connected to a load.

plasma concentration [6] has shown that, in the magnetic hydrodynamic (MHD) mode (n ~ 1016–1017 cm–3), high-density currents and large charges can be passed through POSs, but, in this case, ion flows shunt a POS, and its output voltage is no higher than 2 MV. In the electron magnetic hydrodynamic (EMH) (n ~ 1015–1016 cm–3) and erosion (n ~ 1014–1015 cm–3) modes, the linear (along the circumference of the POS outer electrode) density of the transferred charge is restricted (ql = 2.5–5 mC/cm); however, it is possible to produce a higher voltage that is

As the MXG is enabled, the current in the line rising with time is closed through a plasma jumper. At this stage, the POS impedance is small, and the electric energy of the generator We = CU2/2 is converted into the magnetic energy LI2/2 of the line, where L is the total inductance of the line, generator, and the connecting conductors. The POS impedance then sharply increases, and the stored energy of the magnetic field is released in the POS itself and in the POS-shunting load.

Lg

Lvac

Rpos

C

Rl

Programs for developing superhigh-power generators for experiments on inertial thermonuclear fusion are currently under consideration [2, 3]. The Baikal program [3, 4] seeks to create a current pulse at a level of 50 MA with a duration of ~150 ns at a voltage of up to 10 MV. A POS can be utilized as an output stage. At present, the highest parameters of pulses obtained with the help of POSs on the largest installations are within 3 MA and 2 MV or 2 MA and 3 MV [5].

1

Analyzing the operation of the facilities with POSs in various operating modes determined by the initial

Fig. 1. Circuit diagram of a POS-based generator: (1) capacitive storage (MXG) with the capacitance C and inductance Lg; (2) insulator; (3) POS with the inductance Lvac of the vacuum line, resistance Rpos, and current I; and (4) load resistance Rl.

†Deceased.

2

C

3

4 I

0020-4412/02/4502-0248$27.00 © 2002 åAIK “Nauka /Interperiodica”

A MODERNIZED PC-20 FACILITY FOR STUDYING (a)

249 (b)

1

3 2

4 5

Fig. 2. (a) Photograph and (b) schematic drawing of the PC-20 facility: (1) MXG module; (2) high-voltage feedthrough; (3) insulator with gradient rings; (4) vacuum chamber; and (5) POS.

limited by the shunting effect of electron currents. The voltage Upos obtained at the POS is determined by the energy density wi spent for plasma erosion, i.e., for the acceleration of ions: Upos ≈ βw i . In most of the facilities, the transferred charge density q is almost the same (i.e., wi ∝ UMXG), as was shown in [6] 4/7

U pos [ MV ] = α { U vpg [ MV ] }

4/7

.

(1)

This dependence was checked experimentally for a setup [6] with a factor α = 2.5 (åV)3/7. In order to suppress electron leakage and raise the POS voltage, it was proposed to use an external magnetic field. Earlier experiments at the Taina facility (UMXG = 0.4 MV) [7] with the use of a magnetic field have shown that, for ql ≤ (2.5–5) µC/cm, α = 3.6(MV)3/7. Similar experiments at the PC-20 facility (UMXG = 0.8 MV) [8] yielded the value α < 3.6(MV)3/7 that was explained by the effect of leakage over the insulator. The objective of this work was to update the PC-20 facility for conducting experiments on refining the scaling of obtained voltages and densities of the charge passed through the POS and for revealing the factors that restrict the electric parameters obtained experimentally. The results of these experiments will form a INSTRUMENTS AND EXPERIMENTAL TECHNIQUES

basis for designing a POS for an intermediate åéã facility [4], on which it is planned to increase the basic parameters up to ~3.6 MA and 4–6 MV and to determine ways for advancing to the region of parameters specified by the Baikal program. CIRCUIT, PARAMETERS, AND FEATURES OF THE MODERNIZED PC-20 FACILITY The PC-20 facility-an X-ray sterilizer with a beam power of 20 kW-was built in 1991 [9] and intended for carrying out radiation-biology experiments in a repetitive-pulse (1–2 Hz) mode. Figure 2 shows a photograph and the general scheme of the facility. Four modules of MXG are arranged around the high-voltage feedthrough insulator connecting the MXG with the POS. In order to improve the basic parameters of the facility, the following modifications were introduced to it. (1) Frequency capacitors of the four-module 20-stage MXG (50 kV, 0.2 µF) were replaced by singlepulse capacitors (50 kV, 2.5 µF). In this case, the maximum possible energy store was increased by a factor of 12.5 and amounted to 240 kJ at a maximum output voltVol. 45

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1

(3) A new POS (Fig. 3) design was developed. It contains 78 plasma guns, a solenoid for creating a magnetic field, and POS electrodes. The maximum strength of the quasi-stationary axial magnetic field is ~16 kG. The linear density (along the circumference of the outer POS electrode) of the charge transferred through the POS is ql ~ 9 mC/cm, which is almost twice as large as the limiting density (2.5–5 mC/cm) determined earlier [7]. The diameters of the outer and inner POS electrodes are 18 and 10 cm, respectively.

2 3

4

The POS operates in an external magnetic field (Fig. 3) at the positive polarity of the inner electrode. At the negative polarity, the POS operates without introducing a magnetic field. The POS electrodes are manufactured from a carbon–carbon material because of the following reasons: (a) as the experience of the POS operation in the frequency mode has shown [8, 9], carbon materials are more resistant under pulse actions than stainless steel, tantalum, and tungsten; (b) according to research [10], the energy threshold of plasma production under the effect of electron bombardment in carbon materials is five times higher than for stainless steel; and (c) tests for the resistance of various materials to pulse electron beams (300 keV, 100 ns) have also shown the advantages of carbon materials (these results were obtained by B.A. Demidov and coworkers at the Kalmar facility, see Table 1). The presumable area-average energy deposition density at the electrodes is ~50 J/cm2 per pulse.

Fig. 3. Schematic diagram of the POS: (1) outer electrode (cathode); (2) high-voltage electrode (anode); (3) solenoid; and (4) plasma guns. Lines of force of the magnetic field are drawn between the electrodes.

1 3 2

Fig. 4. Schematic diagram of a plasma gun: (1) grounded electrode of the plasma gun and POS; (2) high-voltage electrode of the gun; and (3) ceramic insulator.

Capillary-type plasma guns with ceramic insulators are used in the POS (Fig. 4). They are located on the surface of the outer POS electrode along three circumferences spaced by 2.5 cm. The guns are combined in six sections with 13 pieces in each section (two sections on each circle). Each section is supplied from a separate capacitor (àä-50-0.4). The guns of each section are distributed uniformly on the circumference.

age UMXG = 1 MV; the current rise time in the MXG–POS circuit increased to 2 µs, and the current amplitude increased to 320 kA. The MXG output capacitance (upon the spark gap operation) is C0 = 0.5 µF, and the inductance of the MXG–POS circuit is L0 = 3.25 µH. The inductances of the vacuum and exterior parts of this circuit are Lvac = 1.4 µH and Lext = 1.85 µH, respectively.

(4) In order to increase the linear charge density ql up to 9 mC/cm, programmable filling of the POS gap with plasma is proposed. The idea is that the POS gap is filled with plasma in several steps, as the plasma erosion develops, and the plasma concentration is maintained at a steady–state level no higher than an allowable value determining the POS operating mode. Thus, being within the EMH or erosion modes, it is possible to pass a higher charge density. For this purpose, the possibility of time–programmable enabling of plasma–

(2) The arrangement of the POS in the vacuum volume was changed. In order to reduce the inductance of the MXG–POS circuit, the outer POS electrode is connected to the vacuum chamber by a cylinder coaxial to the high-voltage feedthrough (Fig. 2b). Table 1. Effect of a beam on various materials Beam density (kA/cm2)/ energy (J/cm2) 10/300 2/60

Material loss, mg/cm2 Type of material loss Splitting-off, mass removal Evaporation Evaporation

Stainless steel

Silicon carbide

80

390

20

Carbon-carbon material 20 8

6

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gun sections is provided. The current in each plasmagun section is monitored with an individual gauge. (5) Additional guard electrodes are placed on the gradient rings of the insulator. They not only protect the insulator surface from UV illumination from the POS volume but also ensure a uniform potential distribution over the insulator surface (Fig. 5) and, consequently, a higher breakdown strength of up to 3.5 MV. In the previous POS design, this distribution was nonuniform and, despite a low average value of the electric field, the voltage at the POS was restricted by the breakdown strength of the insulator to 2.5–3 MV [9]. Note that the POS current was interrupted at a higher rate than the total current in the MXG–POS circuit, which was maintained owing to the insulator leakage currents. (6) The possibility of connecting a variable number of MXG stages to the high-voltage feedthrough via gradient rings is provided, making it possible to vary the density of energy deposition to the POS at the expense of changing the MXG voltage at a constant transferred charge density. Moreover, the possibility of varying the density of energy deposition in the POS at a constant voltage due to changes in the charge density passed through the POS is provided by enabling different numbers (1–4) of MXG modules.

1

Module 1 Lext


Module 2 Lvac

Lext

POS

Ud

Us1 dBm1/dt

The facility uses conventional electrotechnical diagnostic circuits (Fig. 6): a common shunt directly at the POS input, Ipos; shunts in the circuits of each MXG module, Im; a common voltage divider U0 connected to the point at which the inductance of the MXG–POS circuit is split into the vacuum part Lvac and exterior part Lext (MXG inductance); voltage dividers in the first stage of each MXG module, Us; loops for measuring the voltage related to a magnetic-field change, which are set near the connection of a MXG module to the chamber, dBm /dt, and near the POS, dBpos /dt. Typical oscillograms of the signals taken from these sensors are shown in Fig. 7. A large number of sensors makes it possible to verify the accuracy of measurements of the corresponding parameters. In addition, an X-ray detector and integral pinhole chambers were used. The results of measuring the total current of the MXG modules and the POS current coincide to an accuracy of ~10%.

3

Fig. 5. Distribution of the electric field at an insulator segment (3 in Fig. 2): (1) guard electrodes; (2) gradient rings; and (3) polyethylene ring of the insulator.

(7) Operation is ensured at any polarity of the highvoltage electrode with the application of an external magnetic field and without it. The POS design allows three operating modes: short-circuit (in the absence of a magnetic field, the POS is short-citcuited by a dense plasma), no-load (the POS is not short-circuited; upon current interruption, the entire energy is released in it, and a maximum voltage is developed), and intermediate (the POS is shunted by the load) modes. BASIC DIAGNOSTIC CIRCUITS

2

Im1

Ipos dBpos/dt

Im2

Us2

dBm2/dt

Fig. 6. Circuit diagram of electric measurements (two MXG modules are presented): (Ud) signal of the MXG voltage divider; (Us) signal of the voltage divider of the first stage of the MXG module; (dBm/dt) signal from the loop of the MXG module; (Im) shunt signal of the MXG module; (dBpos/dt) signal from the POS loop; (Lext) inductance of the MXG module; and (Lvac) vacuum part of the inductance of the MXG–POS circuit.

The voltage Upos produced at the POS in the current interruption mode was determined by several methods. (i) From the derivative of the shunt-measured current decay, U pos = U res – L 0 dI/dt,

(2)

where Ures is the residual MXG voltage at the moment of current interruption. (ii) From the indication of the voltage divider, U pos = ( U d – U res ) ( L ext – L vac )/L ext , Vol. 45

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Igun Ipos 160 kA

0.40 åV

Ud

where Ud is the divider voltage at the moment of pulse interruption. The voltage-divider signal Us in the first stage contains three characteristic components: during the interval between the operation of the first stage and the entire MXG, we observe a signal Us1 determining the MXG voltage; after the operation of all MXG stages, when the current begins rising, a signal Us2 determines the voltage at the vacuum part of the inductance, U s1 /U s2 = ( L vac + L ext )/L vac ;

Us1 = 42 kV

Us

Us2 2 µs

(b)

at the moment of current interruption, a signal Ud = ~20Us allows for determining the voltage across the POS from formula (3). (iii) From readings of loops dB/dt, U pos = ( U l1 /U l2 )U VPG + U res ,

Igun Ipos

0.40 åV

Ud Ul2 = 3.5 åV

dBpos /dt 2 µs 300 kÄ

(c)

Ipos Im 300 kÄ

1.1 åV

Ud

(5)

where Ul1 and Ul2 are the loop readings at the moments just after the MXG operation and current interruption, respectively. Note that Ul1 corresponds to the initial MXG voltage UMXG. Since establishing the scaling of the voltages obtained with the POS demands their reliable measurement, an additional independent method for evaluating the POS voltage was used.

140 kA

Ul1 = 0.84 åV

(4)

3.5 åV

dBpos /dt 2 µs

Fig. 7. Typical signal oscillograms obtained in the following regimes: (a) short-circuiting, two MXG modules are enabled (20 stages in each), the external magnetic field H = 0; (b) no-load mode, two modules are enabled (20 stages in each), H = 12 kG; (c) no-load mode, four MXG modules are enabled (20 stages in each), H = 16 kG, programmable filling of the POS gap with a plasma is used; (Igun) guns’ current; (Ipos) POS current; (Im) current of MXG modules; (Ud) signal of the voltage divider; (Us) signal of the firststage divider; and (dBpos/dt) loop signal.

ACTIVATION METHOD FOR EVALUATING THE POS VOLTAGE In order to determine the voltage at the accelerator diode, we used a technique of measuring the high-frequency edge of the bremsstrahlung γ-spectrum of electrons accelerated in the diode gap. The γ-spectrum measurements based on the method of filters conventional for electron energies within 1–2 MeV are inapplicable under our conditions. In a range of 1–5 MeV, mass absorption coefficients for all substances very weakly depend on the quantum energy [11]. We measured the short-wavelength edge of the γ-spectrum by the photoneutron activation technique. Two reactions were utilized: 9Be(γ, n)8Be and 2D(γ, n)p with the thresholds EBe = 1.65 MeV and ED = 2.25 MeV, respectively. The yield of hard γ-rays from the accelerator diode in the actual experimental geometry was calculated with the KASKAD computational code [12]. The interaction between the radiation and matter (Be, D2O) and neutron yield were determined as a convolution Nn =

∞ σ (γ, E0

∫

n) Nγ (hν)NBe, D d(hν). The neutrons

produced as a result of each reaction were registered by two similar neutron detectors (similar geometries, components, and sensitivity to the γ-background). The operation of the neutron detectors was based on the activation technique with protracted detection. At first, fast neutrons were moderated in a polyethylene cube; thermal neutrons then interacted with six indium plates located at the cube’s faces with the formation of


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Wall of the vacuum chamber n γ

γ

e–

e–

γ

γ

e–

e–

γ

γ γ γ

n

Neutron detector

Be(D2O)

Cathode

Fig. 8. Schematic diagram of the experiment and calculation for determining the electron energy using 9Be(γ, n)8Be and 2D(γ, n)p photoneutron reactions (two recording channels).

β-active nuclei in the reaction 116In (n, β– )116Sn. Subsequently, the β-particles produced were detected by six gas counters on the exterior sides of the In plates. No absolute sensitivity calibration of neutron detectors was performed; therefore, it was necessary to use the ratio of the readings of two recording channels during measurements. The number of counts in each recording channel was calculated for peak voltages of 2–5 MeV. A schematic diagram of the experiment and the calculations is shown in Fig. 8. In order to increase the yield of γ-radiation, the end and side surfaces of the cylindrical anode were coated by tantalum sheets, which, unfortunately, slightly worsened the POS operation. Calculations were performed in two model versions: for electrons incident onto the anode side and end surfaces. In both cases, electrons fell on the anode surface at an angle of 45°. Figure 9 shows plots of the numbers of counts in two recording channels for these two versions. Curves in Fig. 10 show the ratios of the yields of two photoneutron reactions for these versions. Table 2 lists the counts in two channels, their ratio, and the electron energy obtained. The actual value of the diode voltage can be underestimated for two reasons. The first one is the presence of fasteners covered by tantalum on the end surface of the cylindrical anode, which slightly protrudes from behind a thick cathode; this softens the γ-spectrum at the detector location. The second reason is the deviation of the voltage pulse profile at the accelerator diode from a rectangular profile for which computations were carried out. Both factors lead to a decrease in the D/B ratio of readings of the recording channels. RESULTS OF THE FIRST EXPERIMENTS The results of experiments are shown in Fig. 7. The short-circuit mode is illustrated by oscillograms in Fig. 7a. This mode is implemented in the absence of a ballast resistance in the plasma gun circuit and a large delay (~6 µs) between the moments of the guns’ and the MXG operation, i.e., under conditions of a sufficiently high plasma concentration in the POS gap. In this case, INSTRUMENTS AND EXPERIMENTAL TECHNIQUES

the main divider feeds a voltage to the vacuum part of the inductance of the MXG–POS circuit. The divider of the first stage makes it possible to estimate the ratio between the vacuum part of the inductance and external (inductance of the MXG modules) part from the ratio Us1/Us2 (see formula (4)). The length of the signal Us1 (i.e., MXG delay time) can be varied within a range of 0.2–2 µs by selecting the relation between the MXG charging and self-breakdown voltages. A no-load mode with the use of an external magnetic field, i.e., a regime of maximum voltage at the POS, is illustrated by oscillograms in Figs. 7b and 7c. When two MXG modules are used (i.e., at a linear density of the transported charge ql = 4–5 mC/cm), the probability of reaching a POS voltage of >3 MV is ~50%. The oscillograms in Fig. 7b correspond to the first line in Table 2, which lists the results obtained by the activation technique yielding an energy of electrons of 3.05 MeV. This confirms (if we take into account that this value is underestimated) the data obtained with elecCounts 13360

2 4

1336 1

3

133.6

13.36 3.0

3.5

4.0

4.5

5.0 Ee, åeV

Fig. 9. Counts in the Be (1, 3) and D (2, 4) recording channels for the side surface and base of the cylindrical anode, respectively. Vol. 45

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started, a new plasma portion produced by the second guns arrives. In this mode, the entire MXG charge can be passed and a voltage of 3–3.5 MV can be reached (Fig. 7c). It should be noted that, when the POS gap is programmably filled with plasma, it is much more difficult to keep all the initial parameters constant; therefore, the probability of obtaining such voltage values is small (~4%).

101 2

1

100

CONCLUSIONS 10–1 3.0

3.5

4.0

4.5

5.0 Ee, åeV

Fig. 10. Ratio of the yields of 9Be(γ, n)8Be and 2D(γ, n)p photoneutron reactions for electrons incident onto the (1) side and (2) base surface of the anode.

trotechnical methods that yield a voltage across the POS of 3.2–3.5 MV (see formulas (2), (3), and (5)). This corresponds to calculations using formula (1) with α = 3.6 MV3/7. Experiments with the use of only four stages of a four-module MXG at a charging voltage of 32–48 kV and, correspondingly, an output voltage of 128–192 kV, a current of 200–320 kA, and a charge density of 4−9 mC/cm yield α = 3.2–3.6 MV3/7 for expression (1) [13]; thus, as the linear charge density exceeds its critical value (2.5–5 mC/cm), the amplitude of the resulting voltage decreases. When 20 stages and four MXG modules are enabled (ql = 9 mC/cm), a voltage higher than 3 MV cannot be reached. The cause of this is that an increase in the density and amount of the charge transferred requires an increase in the plasma concentration in the POS and, consequently, the abandoning of the erosion mode. However, precisely this mode favors a rise in voltage most effectively. Therefore, we tried to programmably fill the POS gap with a plasma. For this purpose, the plasma guns were turned on in two steps with an interval of ~6–8 µs and the MXG was enabled ~3 µs later. In this case, the current is initially transferred by a plasma portion produced by the first guns, and, by the moment at which the current interruption could have Table 2 Run number 1 2

Readings of channels, counts Be

D

34 ± 11 32 ± 11

53 ± 12 33 ± 11

Ratio D/Be

Ee , MeV

1.6 1

3.05 ± 0.15 2.85 ± 0.1

As a result of updating the PC-20 facility, a test bench with an energy of up to 240 kJ for investigating a POS in an external magnetic field has been developed. Its design makes it possible to vary the energy deposition density in the POS by changing the number of stages and, correspondingly, the MXG output voltage at a constant value and density of the charge transferred through the POS or by changing the charge value and density and the number of MXG modules, with the voltage being constant. The POS is equipped with independently supplied plasma guns helping to select various programs of filling its gap with a plasma. There are several independent methods for reliably determining the voltage produced at the POS on the test bench. The aforementioned features allow one to solve the problem of determining the limiting POS parameters: voltage and current and charge densities. The voltage obtained in the first experiments is up to 3.5 MV for a MXG voltage of 0.84 MV, currents of 150–300 kA, and a linear charge density of 4.5–9 mC/cm. The voltage obtained coincides with that calculated from (1) with α = 3.6 (MV)3/7. ACKNOWLEDGMENTS This work was supported by the INTAS (grant no. 97-0021) and CRDF (grant no. RP1-2113). REFERENCES 1. Dolgachev, G.I., Zakatov, L.P., Nitishinskii, M.S., and Ushakov, A.G., Prib. Tekh. Eksp., 1999, no. 2, p. 3. 2. Ware, K.D., Filios, P.G., Gullicks, R.L., et al., Abstracts of Papers, 11th Int. Conf. on High-Power Particle Beams, BEAMS-96, Prague, 1996, vol. 1, p. 284. 3. Glukhikh, V.A., Kuchinsky, V.G., Pechersky, O.P., et al., Abstracts of Papers,. 12th Int. Conf. on High-Power Particle Beams, BEAMS-98, Haifa, Israel, 1998, vol. 1, p. 71. 4. Alexandrov, V.V., Azizov, E.A., Branitsky, A.V., et al., Abstracts of Papers, 13th Int. Conf. on High-Power Particle Beams, BEAMS-2000, Nagaoka, Japan, 2000, p. 214. 5. Bugaev, S.P., Volkov, A.M., Kim, A.A., et al., Izv. Vyssh. Uchebn. Zaved., Fiz., 1997, no. 12, p. 38.


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6. Dolgachev, G.I. and Ushakov, A.G., Fiz. Plazmy (Moscow), 2001, vol. 27, no. 2, p. 121.

10. Blinov, P.I., Dolgachev, G.I., and Skoryupin, V.A., Fiz. Plazmy (Moscow), 1979, vol. 8, no. 5, p. 958.

7. Dolgachev, G.I., Zakatov, L.P., and Ushakov, A.G., Fiz. Plazmy (Moscow), 1991, vol. 17, no. 7, p. 699.

11. Tablitsy fizicheskikh velichin. Spravochnik (Tables of Physical Quantities: A Handbook), Kikoin, I.K., Ed., Moscow: Atomizdat, 1976.

8. Barinov, N.U., Belen’ki, G.S., Dolgachev, G.I., et al., Abstracts of Papers, 11th IEEE Pulsed Power Conf., Baltimore, MA, 1997, vol. 2, p. 1222. 9. Babykin, V.M., Chikin, R.V., Dolgachev, G.I., et al., Abstracts of Papers, 9th Int. Conf. on High-Power Particle Beams, BEAMS’92, Washington, DC, 1992, vol. 1, p. 512.


12. Ageev, G.S., Report of Chelyabinsk State Univ., Chelyabinsk, no. 02825090754, 1982, State no. 80 049 937. 13. Barinov, N.U., Dolgachev, G.I., and Maslennikov, D.D., Abstracts of Papers, Int. Congr. on Radiation Physics, High Current Electronics and Modification of Materials, 2000, vol. 1, p. 274.

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