Compact Nanosecond Pulse Generator

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Oral Session tors. This was done to compensate for the stray inductance arising in non-multichannel switching. Finally, one more peculiarity of the HCEIcap 100-0.2 capacitor with external switching [6] is the dynamics of the action of currents on the plates that is responsible for their denser packing. The effect shows up with time as a slight increase in capacitance (within the space factor) and a decrease in gas release due to better contacts between the Al plates and the busbars. The HCEIcap 100-0.2 assembly was tested in the short-circuit mode at a charge voltage of 90 kV. Figure 2 shows a waveform of the current obtained in this mode. It is seen from the waveform that the assembly ensures a current of 200 kA in 100 ns at a charge voltage of 90 kV. diameter 13 m. The amplitude of the load current was 160 kA with a rise time of 120 ns. A typical waveform of the load current is shown in Fig. 4. The voltage across the capacitor was found by the formula: 1 Ut () U0 IC () tdt. C ∫ I, kA U, kV T, ns Fig. 4. Waveforms of the load current and capacitor voltage at a charge voltage U 0 = 87 kV 80 ms/d 200 kA Fig. 2. Waveform of the current in the short-circuit mode at a charge voltage of 90 kV The generator based on the HCEIcap 100-0.2 assembly also contains a load unit (Fig. 3) located through the center of the assembly. The arrangement of the load in the immediate vicinity of the assembly provides low inductance of the busbars and hence a slight decrease in the amplitude of the load current. The peculiarity of the load is that it absorbs a small amount of energy compared to the energy stored in the capacitor. Thus, a voltage reversal greater than 50% arises across the capacitor. This greatly decreases the lifetime of the pulse capacitor that may cause its failure with time. One of the possible ways to suppress this undesirable effect is to use electrically exploded conductors (EEC’s) in the discharge circuit of the capacitor (Fig. 5). EEC Load Fig. 3. X-pinch generator 3. Results The generator was tested for the operation into an X-pinch load. The load was four tungsten wires of 301 Fig. 5. Expected design of the capacitor-switch assembly with EEC’s
Pulsed Power Technology Required parameters were chosen by the EEC algorithm [7]. With these parameters, the EEC’s slightly limit the current during its rise time (Fig. 6, а), but ensure a current cutoff at the instant the energy in the capacitor is close to zero (Fig. 6, b). An example of calculated waveforms of the current and voltage is shown in Fig. 6. The calculation was performed for 30 Cu wires of length 10 cm and diameter 70 µm. I C , kA 370 J/l at an electric field strength of 200 kV/mm. The volume of the active part was 2.3 l. The capacitorswitch assembly in the short-circuit mode produced a current up to 200 kA in 100 ns at a charge voltage of 90 kV. The dimensions of the capacitor active part are Ø80 × Ø160 × 160 mm. The rate of rise of the current at an X-pinch load (four Ø15-m tungsten wires) is 140 kA/70 ns and the X-ray pulsewidth is 2 ns. The peculiarity of this load is that it absorbs a small amount of energy compared to the energy stored in the capacitor. Therefore it was proposed to use exploded wires in the discharge circuit of the capacitor to ensure a current cutoff at the instant the energy in the capacitor is close to zero. Thus, it will be possible to suppress or preclude the oscillation mode of the capacitor and hence to increase its lifetime. References U, kV T, ns а T, ns b Fig. 6. Calculated waveforms of the load current (а) and voltage across different circuit elements (b) Conclusion The compact nanosecond pulse generator was designed and tested. The generator has a specially designed assembly consisting of an HCEIcap 100-0.2 capacitor and a multigap switch. The total inductance of the assembly is 20 nH. The modifications made in the design allowed an increase in energy density up to [1] A.A. Kim, B.M. Kovalchuk, A.N. Bastrikov et al., in Proc. of the 13th IEEE Int. Pulsed Power Conf., 2001, V. 2, pp. 1491–1494. [2] N.A. Ratakhin, V.F. Feduschak, A.A. Erfort, A.V. Saushkin, N.V. Zharova, S.A. Chaikovsky, and V.I. Oreshkin, “Table-top Pulse Power Generator for Soft X-Ray Radiography”, in Proc. of the 14th Int. Symp. on High Current Electronics, Tomsk, 2006, pp. 511–513. [3] V.F. Feduschak, N.V. Zharova, I.V. Lavrinovich et al., “Compact Pulsed Power Generator”, in Proc. of the 15th Int. Symp. on High Current Electronics, Tomsk, 2008, pp. 303–304. [4] N.A. Ratakhin, V.F. Fedushchak, A.A. Erfort et al., “Development of high-current pulse capacitors rated at 100 kV”, in Proc. of Int. Conf. on Physics of Pulsed Discharges in Condensed Media, Nikolaev, 2009, pp. 140–142. [5] A.A. Zherlitsyn, B.M. Kovalchuk, A.V. Kharlov, and E.V. Kumpyak, “Pulsed Current Generator with Variable Pulse Shape”, in Proc. of the 14th Int. Symp. on High Current Electronics, Tomsk, 2006, pp. 287–289. [6] High-voltage capacitor with a built-in controllable switch by V.S. Verkhovsky, N.V. Zharova, I.V. Lavrinovich, and V.F. Feduschak, RF Patent 75783: IPC H 01 G 4/00, H 01 T 2/02, applied 08.04.08, published 20.08.08, Bulletin No. 23 [7] E.I. Azarkevich, A.V. Kobluchko, Yu.A. Kotov, and T.A. Lisetskaya, “Computational model of an electrical-explosion opening switch, High-voltage spark gap and electrical-explosion opening switches”, in Proc. of a Joint Meeting of Scientific Councils of the USSR AS on Scientific Foundations of Electrophysics and Electrical Power Engineering and Problems of Pulsed Power Technology, Tomsk, Nov 27–28, 1986, pp. 109–111. 302
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Compact Nanosecond Pulse Generator

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