Original Report
Characteristics of the High Voltage Divider
Using an Aqueous Solution
（Received on 30， August 1984）
TakekiSAKURAI ToshimitsuWATANABE
Abstract Asimple and an inexpensive voltage divider for the measurement of a high voltage pulse with a fast risetime is developed with an aqueous solution of CuSO4． The characteristics are dependent on the concentration of CuSO4． At a typical concentration of about O．07 mol／1， the distortion of the waveform measured by the divider is 2％，the delay of the risetime is less than 1．O ns and the upper limit of the working frequency for a voltage of a few tens of kV is higher than 200 MHz． Finally the divider is applied to measure the waveform in an actual pulsed discharge．1． Introduction
The measurement of a pulsed voltage is
important to discuss an oscillation mechanism of
the laser excited by a pulsed discharge． A
conventional technique is a direct measurement of
the low voltage divided by a resistance which is made from an aqueous solution． The dividers havebeen developed with the resistive medium such as
copper sulfate solution1）−i3）and sodium thiosulfate solution4）． The division ratio of this divider can be easily selected by the change in the concentration． In addition to this， other characteristics such as arisetime and a distortion of the monitored
waveform are also dependent on the concentration． However， such properties are not exactly described in any papers． Making the characteristics clear is very helpful for the use of this type of divider・ In this paper we describe the experimental results showing the detailed characteristics of the voltage divider depending on the concentration．2． Apparatus
The structure of the developed divider is shown in Fig．1（a）． The equivalent circuit of the divider is shown in（b）in the same figure． The resistance RA is made from CuSO4 solution． A plastic cylinder with an inner diameter of 7 mm and a length of 34 mm stores the solution． The solution is inserted into the cylinder with a syringe through a small hall H drilled on the wall， just before the divider is used． The resistance of 3．7Ω，．R，， consists of six solid resistances of 22Ωplaced coaxially in the cylinder． ＊ Department of Electronic Engineering． ＊＊@Present address：Hitachi Ltd． Tozuka−ku， Yokohama． （o） CuS（㎏SOLUTION CABLE H SOUD RA RESISTANCE 十ELECTRODEb。AXiAL R・HALL SHIELD
CABLE
＝ ＝＝ BNC PLASTIC GROUNDED bONNECTOR CYUNDER ELECTRODE @ SHIELD BRASS VESSEL （b） RB RAHIGH
VOL頂〕E caa，xlAL CABLE Fig． l The structure of the divider（a）and the equivalent circuit（b）．一89一
December 1984 Report of the Faculty of Engineering， Yamanashi University No．35 The output signal is detected through a coaxial cable and a BNC connector which is fixed at one end of the cylinder． It should be noted that R， is much smaller than the characteristic impedance 260f the cσaxial cable． The whole structure is designed to be a coaxial type in order to keep a reactance low． The system including a grounded outer electrode is
covered with a shield brass vessel which is
neCeSSary tO remOVe any eleCtriC nOiSe．3． Characteristics
To check the working characteristics of the divider， a pulsed high voltage generator with outputvoltage up to 2kV was used． The waveform
monitored by the divider is shown in Fig．2． Now we define three parameters， the risetime，τ， which is given by T，−7る， the distortionη， which is given by（1−（∠47．4）／（B’／B））×100， and the magnification ル1，which is the ratio of the voltages applied to the divider and monitored by the divider． The initial time delay To results from the propagating time on the coaxial cable used． The divider made with the solution of CuSO4 has no own time delay on the time scale in Fig．2． The experimentally obtained results of threeparameters are shown in Fig．3as a function of
concentration and 1∼A，Dc which is the resistance measured by a digital meter with DC current of 150μA．The value of RA，Dc is determined from the
concentration of CuSO4． The resistance RA，Dc of this divider is about 2．2 kΩat the concentration of O．07 Fig．2 T1 n （ ͡o
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（50ns／div．） The waveform monitored by the divider （dotted curve）and the voltage waveform from the generator（solid curve）． Fig．3Q20．1 007 004 003
CO、NCENTRATION（mot／1） The experimentally obtained charact− eristics of the divider、mol／1． At the temperature of O°C the maximum
concentration solved in a pure water is about O．89 mol／15）． The value of RA，Dc is increased withdecreasing the concentration of CuSO4． However，
it should be noted that the value of 1∼A，Dc is dependent on not only the concentration but also thestructure of the divider． The measured
magnification〃is agreed with the value calculated
from（1∼A，Dc十R．）／1∼B， where R， in this divider is constant at 3．7Ω． This shows that there is no difference between the values of RA measured in the pulsed voltage and 1∼A，Dc．The distortion η and the risetime τ are
increased with the magnification M as shown in Fig． 3．For an actual use of the divider working at a voltage up to 100 kV， it may not be necessary that the value of Aイis larger than 1000， For example， if M is selected to be 600，τ＝1ns andη＝2％． This monitoredwaveform when the voltage of single square pulse
with the width of 500μs is applied to the divider． We tried to make the divider with R， of 1Ω，The magnification〃is 3．7 times the value shown
in Fig．3and other characteristics are almost the
same as the results in Fig．3． However， the dividermdicates that the upper limit of the working
frequency is higher than 200 MHz． It is also
obtained that the lower limit of the working
frequency of this divider is a few kHz． This ischecked from the distortion．of the
一90一
Characteristics of the High Voltage Divider Using an Aqueous Solution
has a resonance phenomenon at frequencies higher
than 10 MHz． It is found that the optimum value of R，is from 2 to 5Ω． We also made the divider inwhich R， was made from the saturated CuSO4
solution， but it was diffLcult for R， to be much smaller than the characteristic impedance， Z6． 4． Application The divider was applied to measure the voltagebetween electrodes of an actual pulsed discharge
tube． The pulse voltage was supplied to the tubefrom a charge transfer circuit6）． The energy’
charged initially on the condenser CI transfers tothe second condenser （］2 through a spark gap
switch． When the voltage across C， is higher thanthe breakdown voltage of a gas， the discharge
starts． This type of transverse discharge is often used to excite pulse lasers such as an N21aser6）・7） and an excimer laser8）・9）． The voltage measured by the divider is shown in Fig．4 for the case that the initially apPlied voltage across CI is 9．O kV． The spark gap switch fires at time Ts． In Fig．4（a）the helium gas pressure is 80 mbar and after the discharge starts at Td，，thevoltage abruptly decreases． The discharge current
is shown by the dotted Curve in the same figure tocompare with the waveform of the voltage． If
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4 7 （b） ♪幽ジ 1 0 、 ’ 、0
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2 7 臨 b （o） `》A 、 1 0U51
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6
Fig．4 The measured voltage between electrodes of the transversely excited discharge tube at various gas pressures． The dotted curves show the discharge current flowing through the discharge tube． helium gas pressure is decreased to be about l mbar， the breakdown voltage becomes higher and it takes long time to get the breakdown as shown in Fig．4 （b）．The discharge starts at Td，． The breakdownvoltage is again increased with decreasing the
helium pressure frorh l mbar and finally the
discharge does not start as shown in Fig．4（c）． In this case the charge transfers only between CI andGand the curve in（c）is well agreed with the
voltage calculated from the equivalent circuit
parameters． The detailed phenomena of the
ク breakdown in a fast risetime pulsed discharge are now studied with the use of this divider． It should be noted that the divider is available to measure the pulse waveform with peak voltage at least 36 kV． 5． ConclusionThe divider of the high voltage is simply
constructed with the solution of CuSO4． The
characteristics are exactly measured as a functionof concentration of CuSO4 and the divider is
actually applied t．o measure the voltage waveform of a pulsed discharge tube． It is confirmed that thedivider is su箭ciently available to measure the
pulsed waveform with a high voltage up to several tens of kV and with a risetime longer than l ns． The effective working frequency of the divider is fromkHz to a few hundred MHz．
AcknowledgmentsThe authors would like to express their
appreciation to Dr． H， Matsuzawa and Mr． Y． Inoue for valuable discussions．References
1）D．G． Pellinen and S． Heurlin：ANanosecond Risetime Megavolt Voltage Divider， Rev． Sci． Instrum．，42，6， p．824 −827 （1971）． 2）D．G． Pellinen and I． Smith：Reliable Multimegavolt Voltage Divider， Rev， Sci． Instrum．，43，2， p．299−301 （1972）、 3）D．G． Pellinen， Q． Johnson and A． Mitchell：Picosecond Risetime High Voltage Divider， Rev． Sci． Instrum．，45，7， p．944−946（1974）． 4）D．G． Pellinen and M．S． DiCapua：Two Megavolt Divider for Pulsed High Voltages in Vacuum， Rev． Sci． Instrum．， 51，1，p．70−73（1980）． 5）RC． Weast ed．：CRC Handbook of Chemistry and一91一
December 1984 Report of the Faculty of Engineering， Yamanashi University No．35 6） 7） Physics， CRC Press，58th ed．， p． Blll（1977−1978）． M，Geller， D．E． Altman， and T．A． DeTemple：Some Considerations in the Design of a High Power， Pulsed N2 Laser， Appl． Opt．，7， IL p．2232−2237（1968）． W．A． Fitzsimmons， L．W． Anderson， CE． Riedhauser， and
