Compact Nanosecond Pulse Generator

Pulsed Power Technology
Compact Nanosecond Pulse Generator
N.V. Zharova, I.V. Lavrinovich, V.F. Feduschak, and A.A. Erfort
Institute of High Current Electronics SB RAS, 2/3, Academichesky ave., Tomsk, 634055, Russia
Abstract – A compact nanosecond pulse generator
was designed and tested. The generator has a specially
designed unit consisting of an HCEIcap 100-
0.2 capacitor and a multigap switch. The total inductance
of the unit is 20 nH. The modifications
made in the design allowed an increase in energy
density up to 370 J/l at an electric field strength of
200 kV/mm. The volume of the capacitor active
part is 2.3 l. In the short-circuit mode, the unit ensures
a current up to 200 kA with a risetime of
100 ns at a charge voltage of 90 kV. The dimensions
of the capacitor active part are
Ø80 × Ø160 × 160 mm. With an X-pinch load (four
W wires of diameter 15 µm), the rate of rise of the
current is 140 kA/70 ns and the X-ray pulsewidth is
2 ns. The peculiarity of the load is that it absorbs a
small amount of energy compared to the energy
stored in the capacitor. Therefore, it is proposed to
use exploded wires in the discharge circuit of the
capacitor to ensure a current cutoff at the instant
the energy stored 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.
of an HCEIcap 100-0.2 capacitor and a multigap
switch made it possible to design a compact nanosecond
pulse generator operating into an X-pinch load.
Below we consider the generator at greater length.
2. Design of the generator
The generator is based on a capacitor-switch assembly
(Fig. 1) consisting of HCEIcap 100-0.2 pulse capacitor
1 and multigap switch 2 located on the outside of
the capacitor.
1
2
1. Introduction
In the last decade, the design concept of high-power
generators connected in the circuit of line pulse transformers
(LPT’s) was developed at the Institute of
High Current Electronics, SB RAS [1]. LPT’s
equipped on the primary side with pulse capacitors
capable of producing currents of several tens of
kiloamperes in 100–300 ns make it possible to do
away with additional stages of energy compression.
The problem of attaining high pulse currents at a load
in the nanosecond range prompted the design of highcurrent
pulse capacitors rated at 50–100 kV. The energy
from a capacitor is extracted with a switch, and
hence of chief interest is to combine a capacitor and a
switch in a single unit. This allows a decrease in the
inductance of the capacitor-switch assembly (CSA) to
obtain high rates of rise of the current. The result of
works in this area is a series of nanosecond highcurrent
CSA’s rated at a voltage of 50–100 kV and
current of 100–700 kA with a rise time of 100–300 ns
[2–4].
Initially, it was expected to use several CSA’s
connected in parallel with each LPT stage. However,
the capability of the assemblies to produce high currents
in nanoseconds allows their independent use as
generators for various low-impedance low-voltage (up
to 100 kV) loads. For example, an assembly consisting
300
Fig. 1. HCEIcap 100-0.2 capacitor-switch assembly
The HCEIcap 100-0.2 high-voltage pulse capacitor
is rated at a voltage of 100 kV and its capacitance is
0.2 F.
The dimensions of the capacitor active part are
Ø80 mm × Ø160 mm × 160 mm, and its volume is
2.3 l. The energy density of the capacitor is 370 J/l,
and the electric field strength is E = 200 kV/mm.
Unlike the previous HCEIcap 100-0.1 assembly [4],
this capacitor-switch assembly has a longer active part
of 160 mm, a shorter spacing of 3 mm between the
capacitor plates in the sections, and another, lessinductive,
switch. The switch is a multigap switch
developed by B.M. Kovalchuk [5]. The position of the
switch was changed as well: it was arranged on the
outside of the capacitor. All the above changes ensured
a decrease in assembly inductance to 20 nH and
an increase in energy density on retention of the electric
field strength. Another peculiarity of the capacitor
is three busbars rather than one (as is with 50-kV designs)
in each of 57 parallel-connected 100-kV capaci-

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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
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