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A 250 kV Cockcroft-Walton voltage multiplier employing small selenium rectifiers and high frequency power-input
-HO' NTS AND METHODS -,~Z (1965) 242--244 ; 0( NORTH N V C L EA I V*N S T R
A 1,50 kV CO
.,LAND PUBLISHING CO .
CROFT-WALTON VOLTAGE MULTIPLIER EMPLOYING li'_7 CTifIERS AND HICH FREQUENCY POWER-INPUT B . MITRA, H .
. RAHA* anI R. GHOSE
Bose institute, ralcutta Received 4 August 1964 a=-,!ci-aw7 is dtscrnbcd, w1hict uses ~-rs and rf po~vrr at the input . W1 -icn used c~r dr-awing a N:am cur-rcnt of A200 pA, efficierncy has been experimentally decent . H . F. characteristic of single
ckcreft-Watton type voltage multiplier ructed, using small, commercially fiers. It differs from similar insince a fairly high frequency a.c . power has Characteristics of selenium ncy are not very well known. ,hCr circuit has given good results for t'sme. For nearly three years it has been tum voltage deuteron accelerator to We obtained a stable neutron . ix for all this time . the previous construction 4-.)f a genei-ator`), where I mA of beam r-, extracted ai .d accelerated. That in- cd a 50 cycle N oltage-doubler, made `1~21(7~(- 1 h6F -urrent rectifier, tubes. r c tI t-.ue s v,~ crc tirst used by Arnold in a Cockcroft-Walton multiplier . d1lowed and recently another worker') "L-c-d the use of large selenium dry disc rectin ~!jch a ctrcuit . A,mold ern, ploved a frequency of later N% orker used a 60 transformer enirployed a fairly high frequency ht-mcrea ,,~~ in frequcincy at the Inpul. has parts smalle-T . It x~a_s expected that v4 ~,, u iid, alIso b-- smallef . This expectaer fulfifl-_d . as has belen shown by the
s 1, nium cells used as voltage double ,. has been experimentally
obtained upto 100 kc/s. Ripple percentage observeu to be greater than theoretical value but shape of the ripple as observed in oscilloscope records, were unaltered for different lmds, within limits. arranged in 4 stacks,
111
rectifiers N8/200. They are coirnmercially available, small andbeing of light weight, can b- easil7 , ntiounted in a Cockcroft-Walton stack . The manufacturers have supplied the performance data of these 2100 disc rectifiers as a voltage doubler, where a curiTent drainage
of 5 mA at 20 kV was obtained, employing' , frequency of 10 kc/s . Through a private communication we were informed that these could also stand higher frequency,
Iif ofI course the loading were light . To determine the limit of usable frequency with a load to serve our purpose, ckperiments were performed, which are described in the nex -1, section . The consideration of '"load" has been based on the following points : L, With our experience of 14 MeV Tieutron generator'), we came to the- conclusion that for a considerable yield of neutrons by the (t, d) rcaction, witt~ the available thin tritium targets, at about 200 ke',/ deuteron energy, a focussed, unanalysed deuteron beam of 200pA would be more than adequate .
A conswni curreni oi M11A wouid be draine ihrough a bleeder resistance chain of 3000 MQ I i -ii -n by k-orona !c,ss could he kept minin _u carefully rounding LIP of all the sharp points and by keeping the
T3
dctermmed to be ~,hcr su~.h
a con~ ;mtional Cockcroft-",Ialton ~.-ircuiL .Thirty-
s . each o~ \Lfllue 0~02 5 --F and h, ,_-,jng a
de
a' :-,f,
10c,.~ il
lv",J
ati!,0WLC .
thus
with d.c . silicone compound 5 . In the mechanical construction of the stages we have followed Arnold's design, with small modifications here and there. The rectifiers used are selenium SenterCel tubular
191z
I
tach,
stage is insulated from the preceding one by a machined and shaped perspex disc, whose surface has been treated
1,1h
~4
coodensers
realizing 16 doubler stages . Each condense ,.- is placed inside a coronaproof housing of aluminium, and each
1
1
of 8
laboratory dust-free and air conditioned, where humidity Nvzs, hept ver y . low . So in our case it was hoped that the c(. ridition of low load was fl .klfillCd .
Lare has been tak-en for rounding Lip the or i,w corona-discs, corona proofing of condenser-housiigZ, and leads for rectifier connections . The
24 "
Cireat
A 250 kV COCKCROFT-WALTON VOLTAGE MULTIPLIER
243
since the oscillator has bt:en housed inside a shielded control room, away from the accelerator.
a
3. Performance of the inachine 3.1 . Experiments have been performed with 2 discs of selenium detached frorn a N8/200 stick, by making a voltage doubler circuit and drawing loads upto mA, while the frequency, from an input oscillator was varied from 10 kc/s to 100 kc/s. The voltage factor VEF = Jlax,, V)/(d.c. V) were obtained for different frequencies. Fig. I shows the results. For a higher load of 2 mA, it can be seen that percentage of the voltage conversion efficiency (obtained as 100/VEF') is as hign as 60' G, at 100 kc/s .
2
2
I
I
I
lao
40 FRE1QUEP4Cj'
IN
KILOCYCLES 'PER 1111C
too
Fig. 1 . Voltage factor for a doubler circuit made with two seleniwn 4[iscs detatched from SenterCel N8/200, for different high frequencies . A, B and C represent c-unes for load currents of 0.5 mA, 1 .0 mA and 2.0 rnA respectively.
highest voltage end ofthe stack is connected by thick wires to a dome shaped housing, which forms the top of the: accelerator tube and which houses the circuits for ion-source drive, -xtraction and focussing voltage circuits . D.C. silicone compound ' 5 has been freelY used to smear the surfaces exposed, to minimize the growth of r-or-onapoints by adhering dust particles. Power from a three stage, I kW oscillator having a frequency of 100 kc/s, is fed to the multiplier stack by means of a transmission line. This has been necessary -
too
60
MT
ec
80 IN KILOVC , LTS
-20
~40
Fig. 3. Ripple voltage plotted against h.t. in kV, measured during ion-acceleration . the 12. The efficiency of completed voltage multiplier has ')een obtained experi mentally, in the working condition, i .e. while a current was drained as a load in addition to the load currem in a se~)cs resistance blen-der-chain for voltage -neasuremeriL . Th~-oretical multiplication factor negl,--cting ripple voltau etc . v~ 32 in our case . The lutpui (,tc. voltwo 'I ,, me,'isured and 4 b~ a 0"VA'T . j"i L" also nput i i the efficiency : .c. t h'S for diff ~ireai h.t . output anti for diFicrcii -, Ioa6z-. .
90
so Z
6.-
W
,,,:z
c,*
~0
cuRRENT P-TOj,~,A
60
I-L-A 100
So
6o HT
I
I
120
i-
IN KILOVOLTS
t_L_ 140
I
t6io
I
NiClenCy (_)f ti.le multiplier assembly at differcrit hich %'(~Itages
111
0/
3 .3 . Thc ripple voltage, for different load currents has also been measured . It is evidenced by oscilloscope records, that upto a load current of nearly 1000 kA . thc
nat-ire of the ripple does not alter much, although iii, the works of Kato and Kono') has been stated that the form of ~he rupple a1tcrs for voltages higher than
B . MITRA
presumed increased leakage etc. The zititde of the ripple -vollage does not correspond ically obtained from analysis of Nfitchc*111 5 ). In the analysis of the former, 7 ;pp!C Mt S iS §VC1 by &V= A In -4- 1)1.' IC~ in mA, f = frequency in kc/s ; st ce, all -qua]. inpF ; r, = number this bmula, the ripple volt, at 200 yA, ;'s. and for c = 0.025 pF, and z nearly 13 V. Fig. 3 stiows the a,nst Lt . It is seen that the experimenpple is much higher than -aluc . This may be attributed to the m is -not an ideal, rectificr. vio-ur of such a Cockcro -ft-Walton very ssatisfying,, during the entire tof ation of nearly three years. For a 14 roll of a few Times 109 n/s, nearly 100 nalysed) has been drawn and the t-i rn Mall generally used were between tan measurement made from meas-
ei al.
urement of current through a bleeder chain of 3000 MO, made of "Spirameg" resistances. The time constant of the multiplier circuit has been measured to be 8 s. Not much elaborate arrangement of stabilization of the h .t . had been necessary, except electronic stabilization ofthe input h.f. a.c. Almost stable neutron yield (± 5%) has been continuously monitored, upto 2-5 x 10" n/s. The accelerator has been kept in an air conditioned and humidity controlled labor?tory . The authors wish to express their thanks to Prof. M . Bose,, Director, Bose Insi.itute, who initially suggested the construction of such , n accelerator. Financial assistance has been given by the Dept . of Atomic Energy, Government of india.
a
1) B. Mitra, Indian Journal of 11hys . 33 (1959) 149. 2) W. R. Arnold, Rev. Sci. Instr. 21 (1950) 796. 3) R. Dato and T. Kono, Nuct. Instr. and Meth. 15 (1962) 197. 4) A. Bouwers and A . Kuntke, Z. Tech. Phys. IS (1937) 209. 5) R. G. Mitchell, Wireless Eng. 2 (1945) 474.
A 1,50 kV CO
.,LAND PUBLISHING CO .
CROFT-WALTON VOLTAGE MULTIPLIER EMPLOYING li'_7 CTifIERS AND HICH FREQUENCY POWER-INPUT B . MITRA, H .
. RAHA* anI R. GHOSE
Bose institute, ralcutta Received 4 August 1964 a=-,!ci-aw7 is dtscrnbcd, w1hict uses ~-rs and rf po~vrr at the input . W1 -icn used c~r dr-awing a N:am cur-rcnt of A200 pA, efficierncy has been experimentally decent . H . F. characteristic of single
ckcreft-Watton type voltage multiplier ructed, using small, commercially fiers. It differs from similar insince a fairly high frequency a.c . power has Characteristics of selenium ncy are not very well known. ,hCr circuit has given good results for t'sme. For nearly three years it has been tum voltage deuteron accelerator to We obtained a stable neutron . ix for all this time . the previous construction 4-.)f a genei-ator`), where I mA of beam r-, extracted ai .d accelerated. That in- cd a 50 cycle N oltage-doubler, made `1~21(7~(- 1 h6F -urrent rectifier, tubes. r c tI t-.ue s v,~ crc tirst used by Arnold in a Cockcroft-Walton multiplier . d1lowed and recently another worker') "L-c-d the use of large selenium dry disc rectin ~!jch a ctrcuit . A,mold ern, ploved a frequency of later N% orker used a 60 transformer enirployed a fairly high frequency ht-mcrea ,,~~ in frequcincy at the Inpul. has parts smalle-T . It x~a_s expected that v4 ~,, u iid, alIso b-- smallef . This expectaer fulfifl-_d . as has belen shown by the
s 1, nium cells used as voltage double ,. has been experimentally
obtained upto 100 kc/s. Ripple percentage observeu to be greater than theoretical value but shape of the ripple as observed in oscilloscope records, were unaltered for different lmds, within limits. arranged in 4 stacks,
111
rectifiers N8/200. They are coirnmercially available, small andbeing of light weight, can b- easil7 , ntiounted in a Cockcroft-Walton stack . The manufacturers have supplied the performance data of these 2100 disc rectifiers as a voltage doubler, where a curiTent drainage
of 5 mA at 20 kV was obtained, employing' , frequency of 10 kc/s . Through a private communication we were informed that these could also stand higher frequency,
Iif ofI course the loading were light . To determine the limit of usable frequency with a load to serve our purpose, ckperiments were performed, which are described in the nex -1, section . The consideration of '"load" has been based on the following points : L, With our experience of 14 MeV Tieutron generator'), we came to the- conclusion that for a considerable yield of neutrons by the (t, d) rcaction, witt~ the available thin tritium targets, at about 200 ke',/ deuteron energy, a focussed, unanalysed deuteron beam of 200pA would be more than adequate .
A conswni curreni oi M11A wouid be draine ihrough a bleeder resistance chain of 3000 MQ I i -ii -n by k-orona !c,ss could he kept minin _u carefully rounding LIP of all the sharp points and by keeping the
T3
dctermmed to be ~,hcr su~.h
a con~ ;mtional Cockcroft-",Ialton ~.-ircuiL .Thirty-
s . each o~ \Lfllue 0~02 5 --F and h, ,_-,jng a
de
a' :-,f,
10c,.~ il
lv",J
ati!,0WLC .
thus
with d.c . silicone compound 5 . In the mechanical construction of the stages we have followed Arnold's design, with small modifications here and there. The rectifiers used are selenium SenterCel tubular
191z
I
tach,
stage is insulated from the preceding one by a machined and shaped perspex disc, whose surface has been treated
1,1h
~4
coodensers
realizing 16 doubler stages . Each condense ,.- is placed inside a coronaproof housing of aluminium, and each
1
1
of 8
laboratory dust-free and air conditioned, where humidity Nvzs, hept ver y . low . So in our case it was hoped that the c(. ridition of low load was fl .klfillCd .
Lare has been tak-en for rounding Lip the or i,w corona-discs, corona proofing of condenser-housiigZ, and leads for rectifier connections . The
24 "
Cireat
A 250 kV COCKCROFT-WALTON VOLTAGE MULTIPLIER
243
since the oscillator has bt:en housed inside a shielded control room, away from the accelerator.
a
3. Performance of the inachine 3.1 . Experiments have been performed with 2 discs of selenium detached frorn a N8/200 stick, by making a voltage doubler circuit and drawing loads upto mA, while the frequency, from an input oscillator was varied from 10 kc/s to 100 kc/s. The voltage factor VEF = Jlax,, V)/(d.c. V) were obtained for different frequencies. Fig. I shows the results. For a higher load of 2 mA, it can be seen that percentage of the voltage conversion efficiency (obtained as 100/VEF') is as hign as 60' G, at 100 kc/s .
2
2
I
I
I
lao
40 FRE1QUEP4Cj'
IN
KILOCYCLES 'PER 1111C
too
Fig. 1 . Voltage factor for a doubler circuit made with two seleniwn 4[iscs detatched from SenterCel N8/200, for different high frequencies . A, B and C represent c-unes for load currents of 0.5 mA, 1 .0 mA and 2.0 rnA respectively.
highest voltage end ofthe stack is connected by thick wires to a dome shaped housing, which forms the top of the: accelerator tube and which houses the circuits for ion-source drive, -xtraction and focussing voltage circuits . D.C. silicone compound ' 5 has been freelY used to smear the surfaces exposed, to minimize the growth of r-or-onapoints by adhering dust particles. Power from a three stage, I kW oscillator having a frequency of 100 kc/s, is fed to the multiplier stack by means of a transmission line. This has been necessary -
too
60
MT
ec
80 IN KILOVC , LTS
-20
~40
Fig. 3. Ripple voltage plotted against h.t. in kV, measured during ion-acceleration . the 12. The efficiency of completed voltage multiplier has ')een obtained experi mentally, in the working condition, i .e. while a current was drained as a load in addition to the load currem in a se~)cs resistance blen-der-chain for voltage -neasuremeriL . Th~-oretical multiplication factor negl,--cting ripple voltau etc . v~ 32 in our case . The lutpui (,tc. voltwo 'I ,, me,'isured and 4 b~ a 0"VA'T . j"i L" also nput i i the efficiency : .c. t h'S for diff ~ireai h.t . output anti for diFicrcii -, Ioa6z-. .
90
so Z
6.-
W
,,,:z
c,*
~0
cuRRENT P-TOj,~,A
60
I-L-A 100
So
6o HT
I
I
120
i-
IN KILOVOLTS
t_L_ 140
I
t6io
I
NiClenCy (_)f ti.le multiplier assembly at differcrit hich %'(~Itages
111
0/
3 .3 . Thc ripple voltage, for different load currents has also been measured . It is evidenced by oscilloscope records, that upto a load current of nearly 1000 kA . thc
nat-ire of the ripple does not alter much, although iii, the works of Kato and Kono') has been stated that the form of ~he rupple a1tcrs for voltages higher than
B . MITRA
presumed increased leakage etc. The zititde of the ripple -vollage does not correspond ically obtained from analysis of Nfitchc*111 5 ). In the analysis of the former, 7 ;pp!C Mt S iS §VC1 by &V= A In -4- 1)1.' IC~ in mA, f = frequency in kc/s ; st ce, all -qua]. inpF ; r, = number this bmula, the ripple volt, at 200 yA, ;'s. and for c = 0.025 pF, and z nearly 13 V. Fig. 3 stiows the a,nst Lt . It is seen that the experimenpple is much higher than -aluc . This may be attributed to the m is -not an ideal, rectificr. vio-ur of such a Cockcro -ft-Walton very ssatisfying,, during the entire tof ation of nearly three years. For a 14 roll of a few Times 109 n/s, nearly 100 nalysed) has been drawn and the t-i rn Mall generally used were between tan measurement made from meas-
ei al.
urement of current through a bleeder chain of 3000 MO, made of "Spirameg" resistances. The time constant of the multiplier circuit has been measured to be 8 s. Not much elaborate arrangement of stabilization of the h .t . had been necessary, except electronic stabilization ofthe input h.f. a.c. Almost stable neutron yield (± 5%) has been continuously monitored, upto 2-5 x 10" n/s. The accelerator has been kept in an air conditioned and humidity controlled labor?tory . The authors wish to express their thanks to Prof. M . Bose,, Director, Bose Insi.itute, who initially suggested the construction of such , n accelerator. Financial assistance has been given by the Dept . of Atomic Energy, Government of india.
a
1) B. Mitra, Indian Journal of 11hys . 33 (1959) 149. 2) W. R. Arnold, Rev. Sci. Instr. 21 (1950) 796. 3) R. Dato and T. Kono, Nuct. Instr. and Meth. 15 (1962) 197. 4) A. Bouwers and A . Kuntke, Z. Tech. Phys. IS (1937) 209. 5) R. G. Mitchell, Wireless Eng. 2 (1945) 474.