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Decision-making spark chambers
MUCLEAR INSTRUMENTS AND METHODS 32 (t965) 21 7-223 ; C NORTH-HOLLAND PUBLISHING CO .
DECISION-MAKING SPARK CHAM]RERS CH . REY, S . PARKER, B. SHERWOOD and D. SCHWARTZ 7he Enrico Fermi latitute for Nuclear Studki, and the Department of Phyvics, 11niversity of Chicago, Chicago, Illinois I
Received 23 July 1964
A wim spark chamber system has been developed in which information can be analyzod within 30 to 50 nsec of the spark time and used , to trigger other spark chambers for a more . detailed analysis of the same event. The wire chamber system has good spatial resolution, very low nun, a recovery time of less than I ntmand a fast, low.impedance output capable of driving versatile core arrays. Wtunning the wires in simple patterns throughcore arrays, it i possible to get signals whose pulse height is proportional to such things as the number of sparks, ft. number with more'-~.han sotm minimum separation, the I
It is sometimes desirable to improve the selectivity of the' triggering . of Vwk . chambers beyond that ,available from S.0ififillation and 'Cerenkov counter systems. Wire spark chambers have already been developed in which the usual flat metal plates have been .replaced with planes of parallel wires, .and in which the information can b,,-, transferred t-.) a computer using readout devices such as magnetic cores and magnetic tape'), Following a suggestion of V. L. Telegdi that the information from such a chamber might be used directly to trigger other spark chambers, we have developed pulsing and readout techniques that enable logical analysis of such information to be carried out within 30 to 50 nscc of the spark time. I
I
position of a spark and the separation of two sparks . Many other kinds of spatial decisions can be made with these devices such as the recognition of scattering of a particle and coplanarity of two particles. We have used such decision-making spark chambers to trigger an optical spark chamber on two track events . Wires were grouped together at the outputs to give I cm spatial resolution . The observed single track efficiency for one gap was gmter than 99% and the double track efficiency was greater than 97%.
the current causes the core to flip completely, giving a large and relatively constant change in B. For spark currents ranging. from 4 to 40 ampere-turns, there is less than a 20% variation in output pulse height. Since only the first part of the current pulse is needed to flip the core, the output voltage pulse is fast and has little jitter and delay. Typical delay and rise times are about 10 nsec. This signal can provide a useable output pulse providing one can stand off the fury that breaks loose when 5 to 10 kV sparks are striking nearby. Since the 005wnw 006(wnw 06 Wnsec nw Td1, -- 7050 n~ -ec rdr, '60 n, 30 n - rd*8 T,~9n11-C V-36 V/t 50
2. Magnetic core readout When a wire chamber is pulsed, a displacement current appears on all of the ground wires. It has a duration cornpraable to the rise time of the spark chamber voltage -about 10 nsec. If a spark goes to one or more wires, a much larger spark current is added to the displacement current. The spark current has a duration on the order of the fall time of the spark chamber pulse-about 80 nsec: in our chambers . The wireq are usnaliv led thirnugh ferrite
-25 ~ -50,, 10i - ~
enree with
square loop hysteresis curves such as those used in computer memories . The curves for the cores we have used, Indiana General type MC-169, are shown in fig. 1 . An additional bias line is run through the core with a steady current so that the core is normally at point X. Typical displacement current pulses, being fast, follow curves such as the bottom one to the region D-D, giving only a small change in B. If a spark strikes the w;re, the greateir total magnitude and duration of
-1 _-.11-1I- L. - . - , --J40 - 2C, __ I1 ."'.' ___1 30 "-vp6-
J
Fig. 1 . Typical h~stcrcsis curves for Inliana General MC-169 ferrite core. reverse magnetized to saturation (point X) and then magnet ized by currents increasing at rates ranging from 0.05 to 1 .6 am~re-turns per nanosecond. Cross marks ate at 10 nsec intervals. Delay time'% Td (zero current to0 10% of peak secondary output voltage), irise times r, (101%, to 90 /. ofpeak output voltage). and peak output voltages per Secondary turn are also shown . Currents, rather than times are shown for the d.c. curve. Typical measurement en-ors are indicated by the variation in the forward saturation values of B. 217
Cil. REY Ct
,-tualy separated firom the dc. bias *Wtwo lizies are needed through each .-ore : A sipjj line ftom tM ground side of the spark ,cNambo-r through the core to ground and a combination Iine.
al.
for double height or larger pulses . -Such - a chamber''ha-s been constructed for use in an experiment measuring the helicity of ~he positron from muon decay. In this, exp-riment trigIfiers, are desired only for pairs of parFROM
SPARK CHAMBER
JL cum hVic
be carried out with ses. Each core imiter-discriminator. An input line ing through several cores with !e r=d as a multiplexf~r. Several - single ;ore with one read ifmz %trvv " circuniL Several cores with individ") inputs a common read line &,.r,.,,e as a hm1w.-a-lder. bsequent diode discriminator, ,an give -i,utput for one, mo, or more simulinput 11ses (fig. 2)~ Nhmy logical
Redd Lines
L
Fig. 4. Array for trigger on two or, more non-adjacent sparks .
ticles with separations greater than two centimeters, so groups , of ten wires, are joined to single ones that go to the tore. plane. 4,
Or
A
Yes
V Yes +No ~. -r--
-
Anti - Cotm-4&,ce
z"I've-
V
P40
The basic vroblem is that of wo rking. wft. several volt -* output- ssighals, in the immediate pre6ence'of a multi-W .pulse . on the pulsed plane of -the spark chamber w1uch is ='ompanied . by~ gh-freque r, and soak curreit~~ 'Three tiineS of Aettnse are used : 1) The, pulsor, the spark cl*mberthe,readout circuit Low and afl connecting cables are shielded . impedance grounds connect all shielding and the pulser . 2) The circuits are arranged so spurious signals tend to be self-cancelling. One example involv-n the disFROM SPARK CHAMBER
So= basic core configurations,
, which Vves a - .ignal whose 'pliz,ude is proportionai to the numbcr of tracks. k mky cause sparks that go to two adia:cn,~. wires, it is sometimes desirable to make a ,dou")1" logic that gives an output only when more zt-
t
i~iiir one non-adjaz!!n : Adre is driven. Fig. 4 shows
arrangement . Two or more cores will be set of the read lines if and only if two or carry a spark current . These iminator that triggers only
in at. least one
READ L11YES
11ultipte
spark deet=tor .
Fig. 5 . Array for trigger or two or more non-aAjacent sparks with ,lisnhs -:~,rient curnmt cancellatiori . ip"V F.,Uavum irl FillI col-Ees. If the readout line goes through many corcs as in fig. 4, these signals add, becoming larger than the flip signal from a single core . Fig . 5 shows an arrangement in which this signal is cancclled by the displacement cur- , rent of adjacent lines. If ncccssary, a separate cancellation line can be run through the readout cores. 11 can be driven capacitatively from the pulsed plane and can
21 9
DECISION-MAKING SPARK CHAMBERS
use as many turns as necessary for the cancellation . The cancellation scheme shown in fig. 5 reduces the displacement current signal to less than 10% of its original value. 3) The final discriminator is made insensitive to all but the spark signals. The circuit shown in fig. 6 is used to give an output pulse when a double core flip signal appears on any of
the core plane and the d :scriminator chassis produces equal currents down each line which then cancel in the transformer. 'The read lines are threaded through the cores in a symmetric fas1iion and with the minimum possible loop area. This is shown explicitly in fig. 3. For clarity the read lines are only shown schematically in the other figures. 3b) Tlae 33 Q resistors terminate, approximately,
Read Lft
I-
R11w3-4
Some -
-f-,6-f- - - - -
J
ALL DIODES
r
Read>LinQ
IN34A
TRANSISTOR 2N?08
DECIMAL VALUES of CAPACITANCE
I-
-J
RFC
in 0if
INTEGRAL VALUES of CAPACITANCE in pf
: 1 0.1
9
+ core Bias
4F
Fig. 6. Discriminator-adder for array of fig. 5.
the read lines. Diodes D2 add the positive signals from either of the three read lines of fig. 5. These diodes also act as discrim;.iators with a positive bias applied at their cathodc- A ..'vni Cie I kQ potentiometer. The 2N708 provides some furtlier discrimination and amplifies the signal to provide a final output . A bias current for the three rows of cores is provided through a low pass pi filter. Signals in the three units are isolated by 0. 1 pF capacitors between the bias line and ground . The remaining noise has a mean frequency which is higher thaii the signal and is of both polarities . A large part of it is due to oscillations induced by the capacitative coul iling to the pulsed plane of the wire chamber which are, not completely cancelled by the arrangements described in 2). The other components are used to climinae this noise : 3a) Syni,metric circuits and twin input leads are used so that ariy change in the potential difference between
either side of the line formed by the twin leads and their outer shield . 3c) The330 0 resistor and 56 pF capacitor p.-Cferentially attenuate the hash . 3d) Diode D, shorts out pulses of the wrong polarity and suppresses ringing of the transformer. 3e) The 300 pF capacitor preferentially attenuates the hash . 3f) Diode D3 shorts any remaining negative pulses and protects the base-emitter junction of T I . With all this, the hash has become smaller than the signal allowing the remainder to be killed by the discrimination at D2 and at T, . 5. Spark chamber r :covery 2 Methods for operating spark gap pulserS and spark in chamberS3) the multi-kilocycle ran-e have been described. The spark chambers are ustally run with
CH. REY et tzl.
curreeds. A bwp, pulsed clearing field is a sbcni time after the spark has extinguished. added to the usual 90% Ne-10% He tl..e clearing field from causing c exact conc-cntration is not critical and pmsure at O'~ C , ) seems as good as any. xirnum voltaize of 1 .3 M recovery circuit described
remaining charging of C and discharging of the spark chamber field is done through R3 . A typical wave form on the pulsed plate of the spark chamber is shown in fig. 8. 6. Mechaukml The chambers we, have used have 12' x- 12" X active volumes and use 24 0.006" aluminum wires per
Fig. 7. Pulsed clearing field circuit.
;tream, of air past the electrodes id recovery of the spark gap. The ides a pulsed clearing field using a a] diodes. The three 39 92 D, and D2 damp the spark there is no spark. After the pulse. the triodes are turned on strongly and clamp close to ground for 80 as extinguished, the triode is the spark gap voltage to recover. rts up D, and D2 are cut off. clearing field is limited by D3 which clamps the spark ches the reference voltage. 0 Or. till U voltage on C apr ;-Is f ie Then D3 opens and the ~
P-Z-1 C .M.C~ 1. -M
Lncludin-g pulsed clearing field.
inch attached to both sides of 2" wide by J" thick)ucite frames') . A photograph of one chamber with its core plane is shown in fig. 9. Chambers using glass ftames have also been made. A flat strip of 0.012" aluminum with rounded edges is glued to each of the. sides of the frame parallel to the wires and (verlapping slightly the active volume . This is kept at th~. potential of the adjacent wires and prevents the inteasification of field and the resultant edge sparking that may occur when a wire lies close to the frame or crosses it at a small angle . To maintain the wire alignment over a reasonable range oftemperatures without exceeding the yield point of 240 gram, the wires are wound so as to have a tension of 50 gram per wire at 750 F. During the winding, the spacips of the wires is maintained by a layer of double-sided masking tape . Th,,-.- permanent bond ig. made with THinihnnel it) -- ---I -, -11- J . 'm-.- a-11 is made with 0.001" mylar glued to a thin bakelite frame which provides a flat surface for the seal') . It in turn is glued to the main frame. The cumulative tension of all the wires is large enough to cause a bending of the lucite frame sufficient to let the center wires become stack. To prev-nt this slackness, the frames are prestressed while they are being wound . This is not necessary when wider lucite frames or glass frames are used .
DECISION -MAKI XG SPARK CHAMBERS
22 1
Fig. 9. Wire spark charnbcr with core array of fig. 5.
e omance Single and double track cfficicncies were- measured by placing the wire chambers between optical chamQ-s, triggering them on cosmic rays and photographing ^.ach event. The signal from the electronics of fig. 6 was
simultaneously recordel. Plateaus corresponding to one track and two track events were found for variations in the diode bias voltage. The best results were obtained when the rise of the high voltage pulse on the chamber was smoothed by inserting a 20 to 40 Q
CIR . REY et al.
;1
series with the chamber. Typical tingles 0 to 4 V and doubles plateaus from 7
- U-
!;I %. i-t "%' U .. =%, . -' and. the double thau 99* /0 IT
;
L.,
It
C-1-
^I%,-
IF,-V
'11111C
track efficiency was gmter than 97%- With the bias set for double track evcnvs. only I to 2**-" of the single track events gave '.tiznals. Alr)out this mairv are to be expected ftom soft ay , s that do not reach the optica I spark chamber. Reco,miry times were measured by re-pulsing the O-ambcr z&er a sviark aith and without a serond bsence, 2% of the old sparks re-ignited and 4~,, re-ignited after 2 msec~ . In the a second pamicle, the old s;kuk did not remsw- If shorter recovery times are nceded a pulsed clearing fwld without an eWnential Id ve used. 11
1
n wire pairs frorr spark chambers
,
ional logic can be performed quickly and combinations of the patterns shown in : examples are shown in figs. 10 through 13 . 1"vn spark chafter
Cr,
Read Line -digitizrd signal proportional to distances sp,cark from right side of chamber.
~
C-1
a
iNoMtI
V tores
n-1
tares par row
(Positive Signal
Signal)
Il
n-J Cores 2 (Nagatmo Signal
Fig. 12- Amy to give output proportional to maximumseparation oftw9.orukozc,.sMka-
in
fig. 12. If. the two chambers are ali 'ed : withthe bi6atn; . 'ah , undeflected particle will flip an, equal or nearly equal number oftOres in each chamber and the net signal . will be, ;ero,or near,zero- The, d4plamment current signals also cancel. If the spark chamber is driven hard enough so that sparkm- always -go 1o two or- more - adjacent wires the . Circuit of fig. 12 will give a zero or nearly zero output pulse for one such spark and a pulse proportional to the absolute value of the greatest separation, in the direction perpendicular to the wires, for two or more I
'
ws a circuit wilLich gives an output signal
the distance of the spark from the e chamber. If sparks to two or more are present, the signal is proportional to the of the f,-.rthest wdre. SA.atTeTed particles can be detected even though the oun - of the scatter is small compared with the size rn. Orte of several possible methods is shown frlxm spck chamber I
Fig. 13. SYstetn to give trigger on two non-coplanar tracks when uscd with core array of fig . 12.
inve output for scattered particle.
sparki . Aqjacent wires in the circuit can also be driven reliably by using two spark chambers. The output signal can also be used as a warning when the presence of more than one track would deceive sonie other circuit . Four such circuits set up as shown in fig . 13 with thOr outputs fed in-to two analog multiplying circuits
DECISION-MAKING SPARK CHAMBERS
and an adder-discriminator can provide a trigger whenever two tracks are non-coplanar . The only exception to this occurs when sparks occur at a complera,entary set of.points,such. as thoseshownby the open circles. I
We v4sh to thankProfessor V. L Telegdi for suggesting this application Q.,r wire spark chambers . We arO indebted to the Institute for Computer Research, in particular to L-Bounin fdr suggesting a possible readout system using cores and to M. Neumann for many helpful discussions, Wv grateffifly acknowledge the invaluable assistance of T. Nunamaker and J. Horton in the coistruction and testing ofthe chambers. Referomus 1) W.
Galbraith, Rev. Sci. Instr., 32 (1961) 518 .
M. Neumann and H. Sherrard, I.R.E. Trans. Nud. Sci ., NS-9-3 (1962) 259 and NS-9-5 (1962) 5 1, F. Krienen, Nucl. Instr. and Meth., 16 (1962) 262 . F. Krienen, Nucl. Instr. and Meth., 20 (1963) 168. J. Waters, Nucl. Instr. and Meth., 21 (1963) 126. J. Bounin, M. Neumann, R_ Miller and H. SheArard, Nucl. Instr. and Me.th. 30 (1964) 34. M. A. Meyer, Nucl. Instr. and Meth., 23 (1963) 277 . A. L. Aucamp, J. W. Koon, M. A. Mayer, J. J. Van Der Wait and N. S. Wolmarans, Nucl. Instr .and Methods, 26 (1964) 167. M. A. Meyer, J. W. Koen and 1. J. Lessing, Nucl. Instr. and Methods, 23 (1963) 287. W. Galbraith, P. Sbarp and A. Sherwood, Symposium on Nuclear Instruments, Harwell (1%1), Academic Press. X) L. Lavoie, S. Parker, C. Rey and D. Schwartz, submitted to Rev. Sci . Instr. (1964). 3) J. Fischer, G. Collins and W. Higinbotham, Intern. Symp. Nucl. ]Electronics, Nov. 25, 1963, Paris, France. 4) The wire was purchased from Fort Wayne Metals, Fort Wayne, Ind . 5) See ref. 3) for other plastic films which are more impervious to watervapor.
DECISION-MAKING SPARK CHAM]RERS CH . REY, S . PARKER, B. SHERWOOD and D. SCHWARTZ 7he Enrico Fermi latitute for Nuclear Studki, and the Department of Phyvics, 11niversity of Chicago, Chicago, Illinois I
Received 23 July 1964
A wim spark chamber system has been developed in which information can be analyzod within 30 to 50 nsec of the spark time and used , to trigger other spark chambers for a more . detailed analysis of the same event. The wire chamber system has good spatial resolution, very low nun, a recovery time of less than I ntmand a fast, low.impedance output capable of driving versatile core arrays. Wtunning the wires in simple patterns throughcore arrays, it i possible to get signals whose pulse height is proportional to such things as the number of sparks, ft. number with more'-~.han sotm minimum separation, the I
It is sometimes desirable to improve the selectivity of the' triggering . of Vwk . chambers beyond that ,available from S.0ififillation and 'Cerenkov counter systems. Wire spark chambers have already been developed in which the usual flat metal plates have been .replaced with planes of parallel wires, .and in which the information can b,,-, transferred t-.) a computer using readout devices such as magnetic cores and magnetic tape'), Following a suggestion of V. L. Telegdi that the information from such a chamber might be used directly to trigger other spark chambers, we have developed pulsing and readout techniques that enable logical analysis of such information to be carried out within 30 to 50 nscc of the spark time. I
I
position of a spark and the separation of two sparks . Many other kinds of spatial decisions can be made with these devices such as the recognition of scattering of a particle and coplanarity of two particles. We have used such decision-making spark chambers to trigger an optical spark chamber on two track events . Wires were grouped together at the outputs to give I cm spatial resolution . The observed single track efficiency for one gap was gmter than 99% and the double track efficiency was greater than 97%.
the current causes the core to flip completely, giving a large and relatively constant change in B. For spark currents ranging. from 4 to 40 ampere-turns, there is less than a 20% variation in output pulse height. Since only the first part of the current pulse is needed to flip the core, the output voltage pulse is fast and has little jitter and delay. Typical delay and rise times are about 10 nsec. This signal can provide a useable output pulse providing one can stand off the fury that breaks loose when 5 to 10 kV sparks are striking nearby. Since the 005wnw 006(wnw 06 Wnsec nw Td1, -- 7050 n~ -ec rdr, '60 n, 30 n - rd*8 T,~9n11-C V-36 V/t 50
2. Magnetic core readout When a wire chamber is pulsed, a displacement current appears on all of the ground wires. It has a duration cornpraable to the rise time of the spark chamber voltage -about 10 nsec. If a spark goes to one or more wires, a much larger spark current is added to the displacement current. The spark current has a duration on the order of the fall time of the spark chamber pulse-about 80 nsec: in our chambers . The wireq are usnaliv led thirnugh ferrite
-25 ~ -50,, 10i - ~
enree with
square loop hysteresis curves such as those used in computer memories . The curves for the cores we have used, Indiana General type MC-169, are shown in fig. 1 . An additional bias line is run through the core with a steady current so that the core is normally at point X. Typical displacement current pulses, being fast, follow curves such as the bottom one to the region D-D, giving only a small change in B. If a spark strikes the w;re, the greateir total magnitude and duration of
-1 _-.11-1I- L. - . - , --J40 - 2C, __ I1 ."'.' ___1 30 "-vp6-
J
Fig. 1 . Typical h~stcrcsis curves for Inliana General MC-169 ferrite core. reverse magnetized to saturation (point X) and then magnet ized by currents increasing at rates ranging from 0.05 to 1 .6 am~re-turns per nanosecond. Cross marks ate at 10 nsec intervals. Delay time'% Td (zero current to0 10% of peak secondary output voltage), irise times r, (101%, to 90 /. ofpeak output voltage). and peak output voltages per Secondary turn are also shown . Currents, rather than times are shown for the d.c. curve. Typical measurement en-ors are indicated by the variation in the forward saturation values of B. 217
Cil. REY Ct
,-tualy separated firom the dc. bias *Wtwo lizies are needed through each .-ore : A sipjj line ftom tM ground side of the spark ,cNambo-r through the core to ground and a combination Iine.
al.
for double height or larger pulses . -Such - a chamber''ha-s been constructed for use in an experiment measuring the helicity of ~he positron from muon decay. In this, exp-riment trigIfiers, are desired only for pairs of parFROM
SPARK CHAMBER
JL cum hVic
be carried out with ses. Each core imiter-discriminator. An input line ing through several cores with !e r=d as a multiplexf~r. Several - single ;ore with one read ifmz %trvv " circuniL Several cores with individ") inputs a common read line &,.r,.,,e as a hm1w.-a-lder. bsequent diode discriminator, ,an give -i,utput for one, mo, or more simulinput 11ses (fig. 2)~ Nhmy logical
Redd Lines
L
Fig. 4. Array for trigger on two or, more non-adjacent sparks .
ticles with separations greater than two centimeters, so groups , of ten wires, are joined to single ones that go to the tore. plane. 4,
Or
A
Yes
V Yes +No ~. -r--
-
Anti - Cotm-4&,ce
z"I've-
V
P40
The basic vroblem is that of wo rking. wft. several volt -* output- ssighals, in the immediate pre6ence'of a multi-W .pulse . on the pulsed plane of -the spark chamber w1uch is ='ompanied . by~ gh-freque r, and soak curreit~~ 'Three tiineS of Aettnse are used : 1) The, pulsor, the spark cl*mberthe,readout circuit Low and afl connecting cables are shielded . impedance grounds connect all shielding and the pulser . 2) The circuits are arranged so spurious signals tend to be self-cancelling. One example involv-n the disFROM SPARK CHAMBER
So= basic core configurations,
, which Vves a - .ignal whose 'pliz,ude is proportionai to the numbcr of tracks. k mky cause sparks that go to two adia:cn,~. wires, it is sometimes desirable to make a ,dou")1" logic that gives an output only when more zt-
t
i~iiir one non-adjaz!!n : Adre is driven. Fig. 4 shows
arrangement . Two or more cores will be set of the read lines if and only if two or carry a spark current . These iminator that triggers only
in at. least one
READ L11YES
11ultipte
spark deet=tor .
Fig. 5 . Array for trigger or two or more non-aAjacent sparks with ,lisnhs -:~,rient curnmt cancellatiori . ip"V F.,Uavum irl FillI col-Ees. If the readout line goes through many corcs as in fig. 4, these signals add, becoming larger than the flip signal from a single core . Fig . 5 shows an arrangement in which this signal is cancclled by the displacement cur- , rent of adjacent lines. If ncccssary, a separate cancellation line can be run through the readout cores. 11 can be driven capacitatively from the pulsed plane and can
21 9
DECISION-MAKING SPARK CHAMBERS
use as many turns as necessary for the cancellation . The cancellation scheme shown in fig. 5 reduces the displacement current signal to less than 10% of its original value. 3) The final discriminator is made insensitive to all but the spark signals. The circuit shown in fig. 6 is used to give an output pulse when a double core flip signal appears on any of
the core plane and the d :scriminator chassis produces equal currents down each line which then cancel in the transformer. 'The read lines are threaded through the cores in a symmetric fas1iion and with the minimum possible loop area. This is shown explicitly in fig. 3. For clarity the read lines are only shown schematically in the other figures. 3b) Tlae 33 Q resistors terminate, approximately,
Read Lft
I-
R11w3-4
Some -
-f-,6-f- - - - -
J
ALL DIODES
r
Read>LinQ
IN34A
TRANSISTOR 2N?08
DECIMAL VALUES of CAPACITANCE
I-
-J
RFC
in 0if
INTEGRAL VALUES of CAPACITANCE in pf
: 1 0.1
9
+ core Bias
4F
Fig. 6. Discriminator-adder for array of fig. 5.
the read lines. Diodes D2 add the positive signals from either of the three read lines of fig. 5. These diodes also act as discrim;.iators with a positive bias applied at their cathodc- A ..'vni Cie I kQ potentiometer. The 2N708 provides some furtlier discrimination and amplifies the signal to provide a final output . A bias current for the three rows of cores is provided through a low pass pi filter. Signals in the three units are isolated by 0. 1 pF capacitors between the bias line and ground . The remaining noise has a mean frequency which is higher thaii the signal and is of both polarities . A large part of it is due to oscillations induced by the capacitative coul iling to the pulsed plane of the wire chamber which are, not completely cancelled by the arrangements described in 2). The other components are used to climinae this noise : 3a) Syni,metric circuits and twin input leads are used so that ariy change in the potential difference between
either side of the line formed by the twin leads and their outer shield . 3c) The330 0 resistor and 56 pF capacitor p.-Cferentially attenuate the hash . 3d) Diode D, shorts out pulses of the wrong polarity and suppresses ringing of the transformer. 3e) The 300 pF capacitor preferentially attenuates the hash . 3f) Diode D3 shorts any remaining negative pulses and protects the base-emitter junction of T I . With all this, the hash has become smaller than the signal allowing the remainder to be killed by the discrimination at D2 and at T, . 5. Spark chamber r :covery 2 Methods for operating spark gap pulserS and spark in chamberS3) the multi-kilocycle ran-e have been described. The spark chambers are ustally run with
CH. REY et tzl.
curreeds. A bwp, pulsed clearing field is a sbcni time after the spark has extinguished. added to the usual 90% Ne-10% He tl..e clearing field from causing c exact conc-cntration is not critical and pmsure at O'~ C , ) seems as good as any. xirnum voltaize of 1 .3 M recovery circuit described
remaining charging of C and discharging of the spark chamber field is done through R3 . A typical wave form on the pulsed plate of the spark chamber is shown in fig. 8. 6. Mechaukml The chambers we, have used have 12' x- 12" X active volumes and use 24 0.006" aluminum wires per
Fig. 7. Pulsed clearing field circuit.
;tream, of air past the electrodes id recovery of the spark gap. The ides a pulsed clearing field using a a] diodes. The three 39 92 D, and D2 damp the spark there is no spark. After the pulse. the triodes are turned on strongly and clamp close to ground for 80 as extinguished, the triode is the spark gap voltage to recover. rts up D, and D2 are cut off. clearing field is limited by D3 which clamps the spark ches the reference voltage. 0 Or. till U voltage on C apr ;-Is f ie Then D3 opens and the ~
P-Z-1 C .M.C~ 1. -M
Lncludin-g pulsed clearing field.
inch attached to both sides of 2" wide by J" thick)ucite frames') . A photograph of one chamber with its core plane is shown in fig. 9. Chambers using glass ftames have also been made. A flat strip of 0.012" aluminum with rounded edges is glued to each of the. sides of the frame parallel to the wires and (verlapping slightly the active volume . This is kept at th~. potential of the adjacent wires and prevents the inteasification of field and the resultant edge sparking that may occur when a wire lies close to the frame or crosses it at a small angle . To maintain the wire alignment over a reasonable range oftemperatures without exceeding the yield point of 240 gram, the wires are wound so as to have a tension of 50 gram per wire at 750 F. During the winding, the spacips of the wires is maintained by a layer of double-sided masking tape . Th,,-.- permanent bond ig. made with THinihnnel it) -- ---I -, -11- J . 'm-.- a-11 is made with 0.001" mylar glued to a thin bakelite frame which provides a flat surface for the seal') . It in turn is glued to the main frame. The cumulative tension of all the wires is large enough to cause a bending of the lucite frame sufficient to let the center wires become stack. To prev-nt this slackness, the frames are prestressed while they are being wound . This is not necessary when wider lucite frames or glass frames are used .
DECISION -MAKI XG SPARK CHAMBERS
22 1
Fig. 9. Wire spark charnbcr with core array of fig. 5.
e omance Single and double track cfficicncies were- measured by placing the wire chambers between optical chamQ-s, triggering them on cosmic rays and photographing ^.ach event. The signal from the electronics of fig. 6 was
simultaneously recordel. Plateaus corresponding to one track and two track events were found for variations in the diode bias voltage. The best results were obtained when the rise of the high voltage pulse on the chamber was smoothed by inserting a 20 to 40 Q
CIR . REY et al.
;1
series with the chamber. Typical tingles 0 to 4 V and doubles plateaus from 7
- U-
!;I %. i-t "%' U .. =%, . -' and. the double thau 99* /0 IT
;
L.,
It
C-1-
^I%,-
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'11111C
track efficiency was gmter than 97%- With the bias set for double track evcnvs. only I to 2**-" of the single track events gave '.tiznals. Alr)out this mairv are to be expected ftom soft ay , s that do not reach the optica I spark chamber. Reco,miry times were measured by re-pulsing the O-ambcr z&er a sviark aith and without a serond bsence, 2% of the old sparks re-ignited and 4~,, re-ignited after 2 msec~ . In the a second pamicle, the old s;kuk did not remsw- If shorter recovery times are nceded a pulsed clearing fwld without an eWnential Id ve used. 11
1
n wire pairs frorr spark chambers
,
ional logic can be performed quickly and combinations of the patterns shown in : examples are shown in figs. 10 through 13 . 1"vn spark chafter
Cr,
Read Line -digitizrd signal proportional to distances sp,cark from right side of chamber.
~
C-1
a
iNoMtI
V tores
n-1
tares par row
(Positive Signal
Signal)
Il
n-J Cores 2 (Nagatmo Signal
Fig. 12- Amy to give output proportional to maximumseparation oftw9.orukozc,.sMka-
in
fig. 12. If. the two chambers are ali 'ed : withthe bi6atn; . 'ah , undeflected particle will flip an, equal or nearly equal number oftOres in each chamber and the net signal . will be, ;ero,or near,zero- The, d4plamment current signals also cancel. If the spark chamber is driven hard enough so that sparkm- always -go 1o two or- more - adjacent wires the . Circuit of fig. 12 will give a zero or nearly zero output pulse for one such spark and a pulse proportional to the absolute value of the greatest separation, in the direction perpendicular to the wires, for two or more I
'
ws a circuit wilLich gives an output signal
the distance of the spark from the e chamber. If sparks to two or more are present, the signal is proportional to the of the f,-.rthest wdre. SA.atTeTed particles can be detected even though the oun - of the scatter is small compared with the size rn. Orte of several possible methods is shown frlxm spck chamber I
Fig. 13. SYstetn to give trigger on two non-coplanar tracks when uscd with core array of fig . 12.
inve output for scattered particle.
sparki . Aqjacent wires in the circuit can also be driven reliably by using two spark chambers. The output signal can also be used as a warning when the presence of more than one track would deceive sonie other circuit . Four such circuits set up as shown in fig . 13 with thOr outputs fed in-to two analog multiplying circuits
DECISION-MAKING SPARK CHAMBERS
and an adder-discriminator can provide a trigger whenever two tracks are non-coplanar . The only exception to this occurs when sparks occur at a complera,entary set of.points,such. as thoseshownby the open circles. I
We v4sh to thankProfessor V. L Telegdi for suggesting this application Q.,r wire spark chambers . We arO indebted to the Institute for Computer Research, in particular to L-Bounin fdr suggesting a possible readout system using cores and to M. Neumann for many helpful discussions, Wv grateffifly acknowledge the invaluable assistance of T. Nunamaker and J. Horton in the coistruction and testing ofthe chambers. Referomus 1) W.
Galbraith, Rev. Sci. Instr., 32 (1961) 518 .
M. Neumann and H. Sherrard, I.R.E. Trans. Nud. Sci ., NS-9-3 (1962) 259 and NS-9-5 (1962) 5 1, F. Krienen, Nucl. Instr. and Meth., 16 (1962) 262 . F. Krienen, Nucl. Instr. and Meth., 20 (1963) 168. J. Waters, Nucl. Instr. and Meth., 21 (1963) 126. J. Bounin, M. Neumann, R_ Miller and H. SheArard, Nucl. Instr. and Me.th. 30 (1964) 34. M. A. Meyer, Nucl. Instr. and Meth., 23 (1963) 277 . A. L. Aucamp, J. W. Koon, M. A. Mayer, J. J. Van Der Wait and N. S. Wolmarans, Nucl. Instr .and Methods, 26 (1964) 167. M. A. Meyer, J. W. Koen and 1. J. Lessing, Nucl. Instr. and Methods, 23 (1963) 287. W. Galbraith, P. Sbarp and A. Sherwood, Symposium on Nuclear Instruments, Harwell (1%1), Academic Press. X) L. Lavoie, S. Parker, C. Rey and D. Schwartz, submitted to Rev. Sci . Instr. (1964). 3) J. Fischer, G. Collins and W. Higinbotham, Intern. Symp. Nucl. ]Electronics, Nov. 25, 1963, Paris, France. 4) The wire was purchased from Fort Wayne Metals, Fort Wayne, Ind . 5) See ref. 3) for other plastic films which are more impervious to watervapor.