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A new read-out method for wire spark chambers operating in magnetic fields
NUCLEAR INSTRUMENTS AND METHODS 84 (2970) I 3 8 - I 4 0 ;
© NORTH-HOLLAND
PUBLISHING CO.
LETTERS TO THE EDITOR
A NEW READ-OUT M E T H O D FOR WIRE SPARK CHAMBERS OPERATING IN MAGNETIC FIELDS s. KULLANDER, G. LANDAUD, R. LORENZI and J. YONNET CERN, Geneva, Switzerland and University o f Caen, France
Received 13 April 1970 A lumped delay line is used for read-out of a wire spark chamber. Preliminary measurements give a precision better than 0.5 mm and show that multiple sparks can be detected.
A simple scheme used for r e a d - o u t o f wire s p a r k c h a m b e r s is magnetostriction. The p o s i t i o n i n f o r m a tion is defined b y the delayed arrival o f a mechanical pulse. A l i m i t a t i o n o f this scheme is t h a t it can h a r d l y be used in the presence o f strong magnetic fields. In o r d e r to a v o i d this difficulty, b u t m a i n t a i n i n g a time d e p e n d e n t p o s i t i o n i n f o r m a t i o n , electromagnetic delay lines m a y be used. In fig. 1 is shown such a line. The cross section o f the coils is r e c t a n g u l a r ( d x b = 2 x 10 mm2). The coil width is 1 ram, the spacing between coils is 2 m m and there is N = 50 turns in each coil. The capacitances are on 2700 p F each a n d there is a 5% spread a r o u n d this n o m i n a l value. The
delay T for each o f the 69 sections, is 230 ns a n d the characteristic i m p e d a n c e o f the line, Z o = l l 0 f L The pulse-height u across each c a p a c i t a n c e (fig. 2) can be calculated f r o m the formula: u =
INb coT-----~
In
Vd2+x21
LT +x j,
(1)
where ~o = s p a r k frequency ( r a d / s e c ) , b = largest side o f coil (m). With
a s p a r k current I = 1 0 A
Fig. 1. Photo of delay line. 138
10 .7
and
a frequency
139
NEW R E A D - O U T METHOD FOR WIRE S P A R K CHAMBERS
t_i_
u
o
I .
09 = 30x 10 6, w e calculate a pulse height u = 2 v for the line used here. The attenuation ~ of this signal per section depends on the coil geometry and on the coil resistance. For given coils, ~ is proportional to T. The attenuation measured along the 20-cm long line is 3 times. We have tested the delay line in parallel with a magnetostrictive line with well-known properties 1) on a chamber with 1-mm wire spacing. The main features of the electronics used for the lines are a zerocrossing system and a 20 M H z clock1). Output signals from the delay line which correspond to sparks spaced by 4 cm are shown in fig. 3. The only deviations from linearity across the whole line are the fluctuations of the order of 0.2 m m when going from one coil to the next (fig. 2). This should be possible to improve by designing the coils differently.
345
z \
340
0
I
I
I
I
I
I
1
2
3
4
s
6
Fig. 2. Time delay vs position in small steps around three coils.
u
Fig. 3. Output signals for sparks 4 cm apart (2 V/cm; 1/~s/cm).
300_
Z 100_ E
{
0
! ][ . . . . .
_
-1~-qs
o
xL -
o~ 1~ x M
m/m
-I,2-o~ XR
i !
. . . . .
o
q6
-
E
m/m
XM
Fig. 4. Distributions of the differences between position from magnetostriction, XM, and position from delay line, XL or Xrt.
140
s. KULLANDER et al.
In a test with cosmic-ray particles both the right and left outputs of the delay line are used. An area of the spark chamber corresponding to 15 cm along the line is exposed. A standard deviation measurement error a = 0.5 m m is obtained for the differences X L --XM and XR--XM (fig. 4). Part of this error is due to the error in the magnetostriction (0.25 ram) and part of it is due to the 20 M H z clock used for this measurement. We conclude that electromagnetic delay lines are
simple and accurate read-out systems for wire spark chambers operating in magnetic fields. Other advantages compared to magnetostrictive lines are simplicity, reliability and the strong signals induced. Work has been started on the construction of delay lines for read-out of 1 m wire chambers. Reference 1) G. Landaud et al., submitted to Nucl. Instr. and Meth. (1970).
© NORTH-HOLLAND
PUBLISHING CO.
LETTERS TO THE EDITOR
A NEW READ-OUT M E T H O D FOR WIRE SPARK CHAMBERS OPERATING IN MAGNETIC FIELDS s. KULLANDER, G. LANDAUD, R. LORENZI and J. YONNET CERN, Geneva, Switzerland and University o f Caen, France
Received 13 April 1970 A lumped delay line is used for read-out of a wire spark chamber. Preliminary measurements give a precision better than 0.5 mm and show that multiple sparks can be detected.
A simple scheme used for r e a d - o u t o f wire s p a r k c h a m b e r s is magnetostriction. The p o s i t i o n i n f o r m a tion is defined b y the delayed arrival o f a mechanical pulse. A l i m i t a t i o n o f this scheme is t h a t it can h a r d l y be used in the presence o f strong magnetic fields. In o r d e r to a v o i d this difficulty, b u t m a i n t a i n i n g a time d e p e n d e n t p o s i t i o n i n f o r m a t i o n , electromagnetic delay lines m a y be used. In fig. 1 is shown such a line. The cross section o f the coils is r e c t a n g u l a r ( d x b = 2 x 10 mm2). The coil width is 1 ram, the spacing between coils is 2 m m and there is N = 50 turns in each coil. The capacitances are on 2700 p F each a n d there is a 5% spread a r o u n d this n o m i n a l value. The
delay T for each o f the 69 sections, is 230 ns a n d the characteristic i m p e d a n c e o f the line, Z o = l l 0 f L The pulse-height u across each c a p a c i t a n c e (fig. 2) can be calculated f r o m the formula: u =
INb coT-----~
In
Vd2+x21
LT +x j,
(1)
where ~o = s p a r k frequency ( r a d / s e c ) , b = largest side o f coil (m). With
a s p a r k current I = 1 0 A
Fig. 1. Photo of delay line. 138
10 .7
and
a frequency
139
NEW R E A D - O U T METHOD FOR WIRE S P A R K CHAMBERS
t_i_
u
o
I .
09 = 30x 10 6, w e calculate a pulse height u = 2 v for the line used here. The attenuation ~ of this signal per section depends on the coil geometry and on the coil resistance. For given coils, ~ is proportional to T. The attenuation measured along the 20-cm long line is 3 times. We have tested the delay line in parallel with a magnetostrictive line with well-known properties 1) on a chamber with 1-mm wire spacing. The main features of the electronics used for the lines are a zerocrossing system and a 20 M H z clock1). Output signals from the delay line which correspond to sparks spaced by 4 cm are shown in fig. 3. The only deviations from linearity across the whole line are the fluctuations of the order of 0.2 m m when going from one coil to the next (fig. 2). This should be possible to improve by designing the coils differently.
345
z \
340
0
I
I
I
I
I
I
1
2
3
4
s
6
Fig. 2. Time delay vs position in small steps around three coils.
u
Fig. 3. Output signals for sparks 4 cm apart (2 V/cm; 1/~s/cm).
300_
Z 100_ E
{
0
! ][ . . . . .
_
-1~-qs
o
xL -
o~ 1~ x M
m/m
-I,2-o~ XR
i !
. . . . .
o
q6
-
E
m/m
XM
Fig. 4. Distributions of the differences between position from magnetostriction, XM, and position from delay line, XL or Xrt.
140
s. KULLANDER et al.
In a test with cosmic-ray particles both the right and left outputs of the delay line are used. An area of the spark chamber corresponding to 15 cm along the line is exposed. A standard deviation measurement error a = 0.5 m m is obtained for the differences X L --XM and XR--XM (fig. 4). Part of this error is due to the error in the magnetostriction (0.25 ram) and part of it is due to the 20 M H z clock used for this measurement. We conclude that electromagnetic delay lines are
simple and accurate read-out systems for wire spark chambers operating in magnetic fields. Other advantages compared to magnetostrictive lines are simplicity, reliability and the strong signals induced. Work has been started on the construction of delay lines for read-out of 1 m wire chambers. Reference 1) G. Landaud et al., submitted to Nucl. Instr. and Meth. (1970).