405
EXPERIENCE WITH LIMITED STREAMER TUBES
Nahmin Horwitz
Syracuse University
Syracuse, New York 13244 1130
SUllmary
Forty-seven 5-meter longlIarocci" tubes have been assembled
and tested at Syracuse.
These are "standard" Frascati PVC
comb profiles with graphite-coated cathodes with resistance
between .02 and 10 Kn/sq.
A large number exhibited
unacceptably high dark current.
Our observations are
consistent with the hypothesis that the main source of
trouble is insulating spots on the cathode.
One counter was
sprayed With additional graphite to produce a cathode
resistivity of 300 fi/sq.
This counter had low dark current
and exhibited normal charge vs HV.
The cathode was
"transparent" in the sense that the charge induced on B cm x
500 em external pickup
strips was as big as for counters
With high cathode resistance.
This was true for strips on
both the topless side and the graphite side.
406
Intr04uction
In recent months we have 1nvest1~at~d the 8u~tab*1~t,
of limited str,.-er tubes 1 4S lIuon d~tector8 for ~. II ,t
CESR.
This is it. report on our
done by:
Lynn Garren. Rich4rd
e~peri~nctt.
The work
Ho1I1e~. N4ha~n
W4'
HorwU,.
Ab01hassan Jawahery. Pasquale Lubrano. Gi40carlo
"on,t~.
Vivek Sharll&. and Philip Thoma.
Regu1reDl~nts
He require:
i) space
r~solution
Ii) hardware
) .95
~fficiency
'" 1500 II~
ii1) area to be covered
Note that the
anal09~
counte~s
are
~
c.lor1m~t,r.
~o
pulse hei~ht infor...t~on 115 needed and ourll~c~
resolution needs are modest
LST's are
for a
pot~nti,lly
comP4r~
to the....
r,~01ut1on8
HOWever. we do
capable of.
4~,~re
counters that will be:
i) reliable
11) ruC)'C)'ed
111) easy to use
iv) cheap
Parameters of
L~T's
auembl!;!d at
~yra.cui'e
To C)'et hands-on experience we
a~~embled
Syracuse usinC)' 'standard' comb profiles.
supports. etc.
.7 counter$ at
~as env~lo~8.wire
purchased from B1ndi in Italy.
407
5 meters
Collh: length
cells per counter
B
inner cross section of cell
9 )( 9 mm 2
uterial
PVC
coating (done at Frascati by two mellhers
of our group in fall '84)
graphite
.02 to 10 Mn/sq
resistance
wire: diameter
100
~
silver-coated cu-be
uterial
or gold -plated w
gas:
argon:isobutane = 1:2.2
cathode confiquration
topless (see Fig. 4)
Co. .ents on Construction Techniques
1) No clean room, i.e. no attempt to generate a dust-free
atmosphere during
a~ ••ably.
All parts, however, were
washed with alcohol and/or a freon degreaser and the
combs were blown with compressed nitroqen gas before
being sealed into their gas envelopes.
2) Hire stringing, soldering, and heat sealing to wire
supports has been done by hand.
No automated techniques
yet.
3) Each wire is tested immediately after installation to
verify that it can hold> 3600 V (in air) with ( 2
~
408
current draw.
This procedure often locates bad spots on
wire and/or on cathode.
Observed Hire Signals from Cosmic Rays
1 shows <Q wire > vs HV for a typical workinq
counter as well as a sketch of the arranqement under which
Fiq.
the information was obtained.
He observe the usual
transition from proportional to LSH at qas qains of orderof
10 6 and the appearance at hiqher qain of a mode that has
been called limited Geiqer or mUltiple streaaer.
If we were
to operate at 4.7 KV we would qet an averaqe wire charqe of
~
40 pc. Figure 2 shows the transition from proportional
mode to LSH.
Note that proportional:limited streaaer = 1:1
at 4.25 KV and the 10% to 90% transition occurs over an
interval of 350 volts.
HV at which PH:LST
= 1:1
In communication between qroupa the
is a useful number.
It avoids the
problem of someone reportinq the HV at which the efficiency
knee occurs, but neglecting to mention the discriainator
threshold (or qivinq knee and threshold but neqlect1nq to
mention an amplifier prior to the discriminator).
Signals from Ezternal Pickup Strips
Construction
He plan to use ezternal pick up strips both parallel
and perpendicular to the anode wires to qet 2-dimensional
coordinates of all avalanches.
A sketch indicatinq the
409
construction of the strips tested is shown in Fiq.
3.
Overall lenqth and width was 500 x 8 cm 2 for strips parallel
to wires and 40 x 4 cm 2 for .perpendicular strips.
indicated in Fiq.
Also. as
3. we used 1/4"- or 1/2"- thick foam
between signal plane and qround plane rather than I-mm G-IO
in order to qet larqe signals into 50
~.
SOae fActors that didn't affect signal from strip.
Does strip signal depend on whether the strip is on the
topless or qraphite side. or on the resistance of the
cathode? Figure 4 shows the ratio of strip signal to wire
siqnal for both 1/4"- thick and 112"- thick strips located
both on top (topless) and bottom (qraphite side) of the
cathode, and for various cathode
resistances between .02 and
10 MO/sq. Figure 4 can be summarized simply as follows:
Within
t
To
10_. VstriP/Vwire • 0.5 independent of side. foam
thickness. and R.
Efficiencies
To measure efficiencies in a semi-realistic noise
environment. we assembled an array of 15.
shown in Fiq.
Cornell.
5 -meter LST's as
5 and placed it near the accelerator at
Usinq the electronics sketched in Fiq.5 we
measured sinqle strip plateau efficiencies of order 92_.
Sinqles rates were
~
130 Hz.
410
Space Resolution
Space resolution usinq transverse strips
~s
at Cornell, aqain usinq the 15 counter arr.y.
aeasured
Ne~t
to .ach
of the 3 layers of LST's was placed a plane of 4 x 40 ca z
transverse strips.
14 strips per plan. were in.truaent.d
and read out.
Space resolution a y was determined as follows. For
each S1S2 cosmic ray triqqer the centroid of all hits YaS
calculated separately for top, middle, and bottoa l.yers.
Let
y
coq
middle
1
J
ceq
+ Yceq
•
y
bottom
2 ( top
The standard deviation of the Ay distribution
was a.asured
to be 1. 7 cm.
The averaqe number of hits per layer was 1.7 (out of a
maximum possible of 14, and with a 'perfect'
per layer).
~
qivinqone bit
Had we qotten 1.0 hit/layer the expected
resolution would have been (strip
width)/~
• 1.2 ca.
Ability to Hold High Voltlq
The main problem we have experienced to date, is the
small fraction of assembled counters which satisfy our
criteria for holdinq hiqh voltaqe.
Out of
.7 assembled
counters, 20 could be trained within 20-30 hours to hold
411
4.8 KV w1th 1 < 1
~a.
Of these, two subsequently failed.
We have looked at five of the counters that failed (gas
sleeves removed) 1n a luc1te box 1n a dark room and saw blue
spots on the w1res (not on or near w1re supports).
As mentioned above, when tnstal11ng the wires we check
for high-current draw 1n a1r.
p1ece of Teflon
betw~en
When this occurs we run a
wire and cathode.
this does 1nterrupt the current flow.
USU411y
(~
80\)
Having localized the
problem we can then attempt to observe the causes.
Results:
brown spot on wire
wh1te spot on cathode
filament on Wire support
Fi~6
is a scatterplot of maximum HV vs Rcathode (an
average of 10 to 20 measurments made on the horizontal
surface of the comb profile).
It seems clear that at the
highest value of R most counters fail, an4 that the success
rate improves for
low~r
values of R.
The above observations are consistent with the view
held by a number of other groups that poor graph!te coating
is a prime source of trouble (perhaps Halter effect).
ReSUlts with RcathodS
= 300
A/S9
A few days ago we sprayed one of our h1gh-resistance
comb profiles with graphite to produce a rather uniform R
300 Q/sq cathode (again as measured only on the horizontal
surface).
Fi~
7 shows <Qwire) vs HV.
The behavior is no
=
412
different from the well behaved hiqh-R profiles.
counter draws neqliqible current at 4.8 KV.
He
The
also
measured <Qstrip> vs HV and found that <Qtop>I<Qstrip>
c
.41 t .04 and <Qbottom>I<QstriP>
= .57
± .06.
Thus for
our purposes (or for anyone usinq pads with dimensions larqe
compared to 1 cm) both the topless and the qraphite side are
rouqhly 100% "transparent".
There aay be a seaantic problem with the adjective
"transparent".
For us, transparency means the ratio of the
induced charqe on the external pickup
strip to the anode
wire charqe, divided by fractional solid anqle that the part
of the external electrode which sees the avalanche subtends
at the avalanche. Others 2 have defined transparency in
terms of a ratio between the siqnals on a central external
pickUp
strip to that on its nearest neiqhbor.
The latter
definition may be more useful when one is concerned with
space resolution i to the qap size.
Strip efficiencies usinq the R
measured at Syracuse.
The R
= 300
= 300
A/sq comb were
A/sq LST was sandwiched
between four other5-meter LST's servinq as a 4-fold cosmic ray
telescope which then covered all of the area of the counter
beinq tested.
The results are shown in Fiq.
B.
Plateau
efficiencies usinq either the top strip or the bottom strip
were measured to be
~
97%.
413
Plans for Near Future
1)
Test nine more R • 300 Q/sq counters to see if all
demonstrate ability to hold 1 4.8 KV.
2)
...
Asseable and test ten S-meter aluainua profiles.
These
have essentially the same dimensions as the PVC
profiles from Bindi.
They were aade available to us by
Tom Lyons of the MIT qroup.
If alua! nua solves all HV
problems we can qet two dimensional coordinate
information by usinq transverse strips on the topless
aide and either
a) readinq out anode wires or
b) isolatinq the cathode from qround via an
external resistor and takinq a signal from the
cathode itself.
3)
He will also continue to consider the alternatives of
solvinq the HV problem by runninq the counters in the
proportional mode and payinq the price of electronic
amplifiers with an alternative of abandoning external
pickup pads and getting the second co-ordinate via charge
division.
Since the Calorimetry conference we have built and
tested a total of
12,
300 n/sq
5- meter counters.
All hold 4.9 KV, with < 1 ~.
REFERENCES
1.
E. Iarocci, NIM 1!Z, 30, (1983).
2.
G. Battistoni et al., NIM 121, 459, (1982).
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