Instruments and Experimental Techniques, Vol. 43, No. 3, 2000, pp. 328-330. Translated frora Pribory i Tekhnika Eksperimenta, No. 3, 2000, pp. 49--51.
Original Russian Text Copyright 9 2000 by Oleinik.
AND R A D I O E N G I N E E R I N G
An Inductive Voltage Divider
G. M. Oleinik
Troitsk Institute of Innovation and Thermonuclear Research, Troitsk, Moscow oblast, 142092 Russia
ReceivedJune 23, 1999
Abstraet--A small-sized inductive nanosecond pulse-voltagedivider of simple design is described. The divider
is used for measuring the voltage at the output unit of the Angara-5-1 facility.
One of the main problems arising during the operation of high-power pulse generators [1, 2] is the measurement of megavolt voltages with durations of
10-I00 ns. Capacitive [3--6], resistive [7, 8], and (much
more seldom) inductive dividers [9, I 0] are widely used
for this purpose.
Voltage measurements at the outputs of high-power
generators in vacuum, where the load is usually
located, are particularly complex. An intense energy
deposition into the load causes high-power X-radiation.
Under the action of this radiation, the residual gas and
all solid surfaces are ionized. Another ionization source
is the electron flows from the lines with magnetic insulation, which are utilized in such generators. The
appearance of a plasma on the surface of a resistive
divider and in the high-voltage gap of the capacitive
divider may result in a significantly distorted signal.
In order to avoid the effect of leakage currents in a
plasma on the divider readings, the latter must have a
sufficiently low impedance. For this purpose, an electrolytic solution is often used as a resistor in resistive
dividers. In this case, the divider design resembles the
design of an accelerating tube with a set of gradient
rings and a great number of gaskets , which naturally
increase the divider dimensions.
The difficulties mentioned above are partially
removed when using an inductive divider. The appearance
of a plasma expanding even with a velocity of 106 cm/s on
its surface does not lead to a significant change in the
impedance of the high-voltage arm. The inductive
divider has an appreciably simpler design than a resistive one.
This paper describes an inductive divider design for
measuring the voltage at the output unit of the Angara-5-1
facility . It differs from the previous divider operating with this facility  by smaller dimensions and,
consequently, higher operating frequencies.
The divider design must be matched to the unit
intended for voltage measurements. Figure 1 shows a
schematic sectional view of the output unit and a load.
In the vicinity of the load (points 2, 4, 6 and 10), Fig. 1
shows the vertical section running along the module
axis and along the bisector between the directions of
two adjacent modules (to the left and to the right from
the axis, respectively). The output power of each generator module is transferred to the common load along
vacuum magnetically insulated transmitting lines
(MITLs). Eight MITLs from the modules pass through
the chamber wall and converge at the center. The exterior MITL electrodes are connected to the anode collector 2 and are supported by four columns 3, and the interior high-voltage electrodes are connected to the cathode collector 4 and are supported by a single column 5.
A load 6 (a liner  or a Z-pinch ) is connected
between the collectors.
The high-voltage part of the divider is formed by a
metallic rod 7 15 cm long and 2 mm in diameter connected to the cathode and anode electrodes. The lowvoltage part is formed similar to  by a loop 8
located in a cavity 9 in the immediate vicinity of the
rod, so that the signal from this loop depends only on
the rod current. The cavity plays the role of a shield
protected the signal from other currents flowing in the
Similar to , the rate of current variation along
the rod is proportional to the voltage between the anode
and cathode. The signal from the loop is proportional to
the rod current variation rate and, thus, is proportional
to the anode--cathode voltage. The proportionality factor can be easily determined in calibration.
The inductive divider measures the voltage between
the anode and cathode at the point where the currents of
individual modules are added, i.e., along the separatrix,
which is the surface separating the family of magnetic
lines of force embracing the liner axis from eight families of magnetic lines of force, which embrace eight
M1TL cathodes of eight different modules.
The frequency properties of the inductive divider
are determined by the high-voltage part. The latter can
be regarded as an inductance at the moment when wave
processes in the circuit terminate and a quasi-stationary
current distribution establishes; i.e., in a time interval
longer than D/c (D is the divider size and c is the velocity of light). For the divider with the circuit dimensions
1.2 x 2.2 m described in , the time resolution was
0020-4412/00/4303-0328525.00 9 2000 MAIK"Nauka/ lnterperiodica"
AN INDUCTIVE VOLTAGE DIVIDER
Fig. 1. Schematicsectionalview of the outputunit of the Angara-5-1 facility:(1) MITL; (2, 4) anode and cathodecollectors,respectively; (3, 5) columns for supporting the anode and cathode electrodes,respectively;(6) load; (7) metallicrod; (8) loop; (9) cavity
for the loop of the voltagedivider; and (10) location of the B-dot probe.
~10 ns. For our divider, the circuit dimensions are
0.3 x0.2 m, resulting in a time resolution o f - 2 ns.
Reduced dimensions of the divider became possible
due to a decrease in the diameters of the anode and
cathode collectors from 700 mm  to 130 mm (in
The low-voltage part of the divider (loop) does not
distort the signal at times longer than L22/p, where/-22
is the loop self-induction coefficient, p = 50 fl is the characteristic impedance of the cable, which is the load for the
loop. For a l-cm loop, this time is much shorter than 1 ns.
As we see, the cathode is connected to the anode by
two conductors, the metallic rod of the inductive
divider and supporting column, and seems to be shortcircuited to the ground. However, no significant shortcircuiting occurs, because the inductance of these two
conductors connected in parallel is -100 nil, and the
inductance of the load is below 10 nil.
The operation of the inductive divider was tested in
experiments with a load 6 in the form of a heavy metallic cylinder that did not change its geometry in shots. In
this case, the current rise rate in the load and the voltage
at the separatrix must be proportional to each other, and
the proportionality factor be equal to the inductance
determined by the magnetic flux between the separatrix
and surface of the metallic cylinder.
Figure 2 shows the oscillograms of signals from the
inductive divider and B-dot probe 10 measuring the
current rise rate in the load. This B-dot probe is a loop
.placed at a distance of 55 mm from the vertical axis. It
is clearly seen that the signals are proportional to each
other. The difference in the signals appearing after 830 ns
INSTRUMENTS AND EXPERIMENTALTECHNIQUES
is related to the filling of the current-measuring loop
with a plasma.
The inductive divider described has a nanosecond
time resolution, is simple in design and service, is
slightly affected by surrounding plasma flows, and is
a reliable sensor.
U, 102 kV
~ ' ~
Fig. 2. Testing of the inductivedivider. The voltage at the
separatrix measuredby the inductivedivider(solid line) and
the product L dlldt (dashed line), where L = 3.2 nH is the
inductance (up to the separatrix) of the continuousincompressible metalliccylinderset on the axis and I is the current
in this cylinder.