Investigation of the Operation of a Compact Pulsed Generator for Powering a Neutron Tube
Abstract Generated abstract
This paper describes the design and testing of a compact pulsed-voltage generator intended to power the accelerating tube of a borehole neutron generator. The generator was designed to deliver negative pulses of 120 kV at 50 Hz, using inductive rather than resistive charging and isolation elements to reduce losses and control spark-gap behavior. Experimental tests compared duralumin and steel spark-gap electrodes under representative discharge conditions, showing stable breakdown voltage for steel over 78 hours and progressive deterioration for duralumin. The completed seven-stage generator, built with KOB-2 capacitors and sealed spark gaps, produced pulses into a 12 kOhm load with a rise time of about 1.3 microseconds and a duration of about 6 microseconds.
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STUDY OF THE OPERATION OF A COMPACT PULSED GENERATOR FOR POWERING A NEUTRON TUBE
G. A. VOROB'EV, A. I. GOLYNSKII, N. S. RUDENKO
A compact pulsed-voltage generator (PVG) was developed and constructed for powering the accelerating tube of a borehole neutron generator. The PVG produces pulses of negative polarity with an amplitude of 120 kV and a repetition rate of 50 Hz. On the basis of these operating conditions, the electrical circuit of the PVG was selected. Charging through active resistances would have led to large energy losses in them. Therefore all resistances were replaced by inductances.
Fig. 1.
The electrical circuit of the PVG is shown in Fig. 1. The isolating inductances were selected from the condition that no more than 10% of the load current should be lost in them. The value obtained was 22 mH. These inductances were wound with thin wire on Plexiglas frames and had unclosed iron cores. In determining the magnitude of the inductance of the charging choke, the requirement was that, after triggering of the PVG, an arc should not arise in its first spark gap.
If the inductance of the choke is taken to be large, then the dimensions of the choke itself will be large. Taking this into account, the choke inductance was taken as 4 H. In developing the PVG, studies were carried out to select the material of the spark gaps. Burning of the electrodes leads to a change in the breakdown voltage, and this may result in the PVG ceasing to operate after some time. A pair of duralumin and a pair of steel electrodes were tested. The tests were conducted in air at atmospheric pressure; the discharge frequency was taken to be the same as that for which the PVG operation was designed, i.e., 50 Hz; the discharge capacitance was taken equal to the capacitance of a PVG stage.
(1000 pF), and the load was equal to the equivalent load of one stage of the impulse-voltage generator. Figure 2 gives the test results in the form of graphs. As can be seen from the test results, the breakdown voltage of the steel electrodes did not decrease at all over 78 hours of operation, whereas the breakdown voltage of the duralumin electrodes decreased throughout the entire run. On the basis of these experiments, steel was selected as the electrode material.
Fig. 2.
(Graph labels: vertical axis \(U_{\text{br}}\), kV; horizontal axis \(t\), hours; “duralumin spark gaps”; “steel spark gaps.”)
Fig. 3.
The spark gaps of the impulse-voltage generator are placed in a sealed chamber.
The impulse-voltage generator has seven stages, each with two capacitors of type KOB-2 \((U_{\text{op}} = 20\ \text{kV},\ C = 500\ \text{pF})\). The capacitors and the isolating inductances are mounted on Plexiglas strips, which give rigidity to the entire structure.
When discharged into an active load \((R_{\text{load}} = 12\ \text{k}\Omega)\), the impulse-voltage generator produces a pulse whose shape is shown in Fig. 3. From processing the oscillogram it was determined that the rise time of this wave is \(\tau_{\phi} = 1.3\ \mu\text{s}\), and the wave duration (without negative overshoot) is \(\tau_{\text{w}} = 6\ \mu\text{s}\).