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Muon system based on streamer tubes with time-difference readout
Nuclear Instruments and Methods in Physics Research A265 (1988) 137-140 North-Holland, Amsterdam
137
MUON SYSTEM BASED ON STREAMER TUBES WITH TIME-DIFFERENCE READOUT V.M. A U L C H E N K O , B.O. B A I B U S I N O V , A.G. C H I L I N G A R O V , M.Yu. L E L C H U K a n d A.B. N O M E R O T S K Y Institute of Nuclear Physics, 630090, Novosibirsk, USSR
A time-difference technique for the measurement of the coordinate along the wire has been investigated in streamer tubes connected in series. A resolution of 15 mm has been obtained for 5 tubes with a total length of 15 m. The detailed study of nonlinearity of time-coordinate relation was performed for a 8-tube chain with a total length of 10.6 m.
1.
Introduction
The study of a method of coordinate measurements along the anode wire using leading edge timing at the opposite ends of a streamer tube is presented in this paper. The possibility of streamer position measurement with an accuracy of several millimeters using this technique was tested recently [1,2]. This possibility is provided firstly by the excellent time features of streamer pulses, i.e. the short rise time, large pulse amplitude, limited dynamic range and secondly by the use of fast discriminators and advanced TDCs with a 10-20 ps resolution and small intrinsic nonlinearity. We investigated resolution, nonlinearity and calibration problems with emphasis on the series connection of tubes in a long chain (up to 15 m). This approach decreases considerably the number of readout channels and can be used in muon identifiers where the particle flow is sufficiently low. 2. Time-difference technique The time difference between the pulses arriving at the opposite ends of the tube is measured to determine the streamer position along the wire. The coordinate Z is proportional to the obtained time difference with a coefficient 1,'/2 - where V is the pulse propagation velocity in a tube. V is approximately equal to the speed of light in vacuum. Thus, the conversion coefficient T / Z is equal to 6.7 ps/mm. If compared to the charge division technique, timing has some advantages among which we mention the following: - only one digital convertor is required instead of two; an anode wire with smaller resistance and, consequently, with larger diameter can be used providing the reliable operation in the streamer mode and a simple design of streamer tubes; 0168-9002/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
the utmost attainable resolution for the time-difference technique is considerably better than for charge division [31. Both techniques were compared in detail in ref. [1,3]. The dependence of the input-output delay on the discriminator versus the form of the input signal leading edge is the most essential for the understanding of the factors governing the resolution and nonlinearity. Let us consider a conventional discriminator with a constant threshold. Then if the transmission process changes the pulse shape due to attenuation and reflections, delays on the start and stop discriminators may not compensate each other. This results in nonlinearity of a reconstructed coordinate. This nonlinearity depends on the signal amplitude. Therefore the range of pulse amplitudes degrades the resolution of the streamer position. The attenuation due to the wire resistance, in the first order of magnitude, leads to a linear addition in the time-coordinate relation and is equivalent to the reduction of the propagation velocity in the tube. The reflections, however, are essentially nonlinear factors because the reflection distorts the measured time difference only if the delay between the parent and reflected signals is less than the time between the beginning of the signal and the moment of the switching of the threshold element in the discriminator. This condition is fulfilled only in the vicinity of the tube ends. Using a series connection of tubes we inevitably insert perturbations in the transmission line. This leads to reflections and, as a result, to the linearity and resolution degradation. Hence, the investigated problem was whether the electronics used could give a sufficiently high accuracy for the series connection of a large number of tubes and how the accuracy degraded at the ends of the multitube chain where the amplitude difference between the signals arriving at the opposite discriminators was extreme. -
IV. PARTICLE IDENTIFICATION
138
V.M. Aulchenko et al. / Muon system based on streamer tubes
3. Streamer tubes
Measurements were carried out with tubes made of stainless steel with diameters of 20 and 40 mm and wall thickness of 0.2 and 0.3 mm respectively. A C u - B e anode wire with the diameter of 100 txm had a tension of 350 g. The tube ends were sealed by plastic plugs with a brass pin for a wire at the axis. Gas flowed through special inlets. Three-component gas mixtures at atmospheric pressure composed of A r - C O 2 - e t h a n o l or A r - C O 2 - n - p e n t a n e in various concentrations were used. Carbon dioxide passed before mixing through the purification system of silica aerogel and activated carbon. The series gas supply was used for several simultaneously operating tubes. In our previous work [2] the streamer mode was investigated for various gas mixtures, different cathode materials and diameters and different thicknesses of anode wire. At present the ageing effects for different anode materials are under detailed study. In tubes with a diameter of 20 mm the typical parameters of streamer pulses are as follows: a rise ime of about 3 ns, a total width of about 35 ns, an average pulse height about 3 mA, pulse height spectrum fwhm 50-70%. Operational voltage is 5200 V for A r - C O e - n pentane (l : 2 : 1) gas mixture.
4. Electronics
The electronics channel includes two front-end discriminators, a time stretcher and a direct counting T D C . The block diagram is presented in fig. 1.
The transmission line composed of several streamer tubes is terminated with a 230 ~2 resistor. This value was chosen by special optimization. The discriminators are positioned directly at the ends of the tubes and are connected to the stretcher by twisted pair cable. The signal from the time stretcher is fed into the T D C also by a twisted pair cable 20 m long. The time-coordinate calibration of the chain was made using the connections between the tubes. Duration of the stretcher output signal is proportional to the time difference between start and stop signals. The stretching coefficient is determined by the required resolution, the T D C time binning and the dynamic range. For these measurements the 12-bit T D C with the binning of 2 ns was used. With a chosen stretching coefficient of 80 the binning of the time channel was equal to 25 ps corresponding to a position resolution of 1 mm (here and below resolution means the rms deviation). The stretching is based on the charging of a capacitance by a large current followed by its discharge by a small current. The maximum stretching time difference is 120 ns. The maximum error caused by the differential and integral nonlinearities of the stretcher does not exceed 50 ps (input time). Discriminators based on the K 5 0 0 L P l l 6 integrated circuit were used. The intrinsic resolution (limited by time jitter) was measured to be 18 ps. The delay time of the discriminator depends on the pulse amplitude with a slope of about 6 p s / m V (in the region of typical amplitudes). The total thermal drift in the 2 0 - 6 0 ° C range does not exceed 15 p s / ° C. All electronics used was
i t(me
slretclter __J
.~'o~
.~eset
L--~
L ~ ~ L ~
V
,
~ ' L •
.
I;
~ATAWAY
Fig. 1. Schematic diagram of the electronics used for the time difference technique. The chain of streamer tubes is shown in the left upper corner. Calibration signals can be fed into the end of tubes.
139
V.M. A ulchenko et al. / Muon system based on streamer tubes
designed a n d built in the Institute of Nuclear Physics at Novosibirsk [4].
5. Results o | the m e a s u r e m e n t s First of all we tested the possibility of achieving high resolution for several tubes connected in series. The m e a s u r e m e n t s were carried out for tubes of 3 m length with a diameter of 40 ram. Streamer signals were produced with the help of a n 55Fe source. F o r the irradiation the tubes had special windows covered with mylar. T a b l e 1 shows the resolutions o b t a i n e d for the chains with different n u m b e r s of tubes. T h e electric c o n n e c t i o n was provided by an unshielded wire c o n d u c t o r a b o u t 10 c m long. T h e gas m i x t u r e was (20% A r - 8 0 % C O 2 ) - e t h a n o l . The operational H V was 5600 V. In the table S1 denotes the resolution in the middle of the chain; $2 is the resolution at a distance of 10 cm from the ends of the chain. Similar resolution was o b t a i n e d with the collimated
9°Sr source. H a v i n g a series c o n n e c t i o n it is c o n v e n i e n t to calibrate the tube chain in c o n n e c t i o n points. Special attention, however, should be paid to diminishing transmission line i n h o m o g e n e i t i e s causing signal reflections. W e have studied in detail the d e p e n d e n c e of the resolution versus the source position along the wire for the 4-tube chain with a total length of 4 m. The diameter of the tubes was 20 ram. The c o n n e c t i o n s between tubes were m a d e by strips of 0.3 m m width a n d a b o u t 40 m m length o n the printed circuit board. H V and calibration signals were fed into the centers of the c o n n e c t i n g strip. Fig. 2 shows the general view of the m o d u l e consisting of 12 similar tube chains put into two layers. The tubes of adjacent c h a i n s alternate with one a n o t h e r to m a k e negligible the p r o b a b i l i t y of simultaneous hitting
50 ¸
RESOLUflON, 'ram
25
Table 1 Resolution at the middle of a chain (S1) and at 10 cm from the ends ($2) for chains with different numbers of tubes Number of tubes
Length (m)
1
3
3 5
9 15
$1 (mm) 10 13 15
$2 (ram) 20 35 50
2
3
PtJ$1TION,~
Fig. 3. Resolution vs position for 4-tube chain. Hatched regions correspond to connections between the tubes. Discriminator thresholds are 10 mV. Average pulse height is about 200 mV.
Fig. 2. View of the streamer tubes module. Alternating tubes from the same layer are composed in chains with series connection. IV. PARTICLE IDENTIFICATION
V.M. Aulchenko et al. / Muon system based on streamer tubes
140
N t5 ~0 5
The large pulse height a n d the low threshold that are i m p o r t a n t for high accuracy may lead to a cross-talk, especially for the chain solution where conductors connecting the tubes are positioned close to each other. For 10 m V discriminator thresholds the pulse height causing a false hit at the adjacent c h a n n e l was found to be 350 m V in the worst case for two 8-tube chains arranged in the alternating structure m e n t i o n e d above.
6. Summary S,'mrn Fig. 4. Histogram of differences between measured and fitted positions for one of the channels. The rms deviation is equal to 10 mm that corresponds to position accuracy in a tube of 12 mm (see text).
two tubes belonging to the same chain by one particle. T h e amplitude d e g r a d a t i o n due to the a t t e n u a t i o n a n d reflections was f o u n d to be a b o u t 25% in the worst case. The d e p e n d e n c e of the measured resolution versus the posit!on is plotted in fig. 3. G a s mixture C O 2 - n - p e n t a n e (3 : 1) was used (HV 6000 V, average a m p l i t u d e 200 mV at 230 ~2). Three similar modules were tested with cosmic ray particles. Two scintillation counters 20 x 20 cm served for a trigger. The efficiency of the m o d u l e to m i n i m u m ionizing particles at H V of 6000 V was higher t h a n 99%. Six points per track were fitted with a straight fine. T h e histogram for the difference between the m e a s u r e d a n d fitted coordinate for one of the c h a n n e l s is presented in fig. 4. The rms deviation of the presented spectrum is 10 ram. This corresponds to a 12 m m resolution at one tube if one assumes equal resolution in all tubes. W i t h o u t any corrections for calibration shifts the average resolution goes up to 25 mm. T h e tube chain length in these m e a s u r e m e n t s was 4 m. Detailed study of nonlinearity was p e r f o r m e d for 8 tubes of 1.15 m length with a d i a m e t e r of 40 m m connected in series. The time-coordinate relation was o b t a i n e d with a 9°Sr source for A r - C O 2 - n - p e n t a n e ( 1 : 2 : 1 ) gas ( H V 5200 V, average a m p l i t u d e of 150 mV). The pulse height decreased b y 55% after the p r o p a g a t i o n from one end of the chain to the other. T h e m e a s u r e d points of time-coordinate relation were fitted b y a linear function with 3 parameters: the reference point, the slope, a n d the effective length of the conductor between the n e i g h b o u r i n g tubes in the chain. T h e largest nonlinearities of 40 m m were observed at the ends of the chain. T h e rms deviation from linearity over the total length of 10.6 meters is 14 mm, which is c o m p a r a b l e to the resolution.
The o b t a i n e d resolution a n d nonlinearity are in a n accordance with the values expected from the properties of the electronics used. It is clearly seen that discriminators with a lower effective threshold or discriminators with a c o n s t a n t fraction threshold could advance the position accuracy. But that requires new more sophisticated electronics design. A t present studies in b o t h directions are in progress. The investigated time difference technique is p l a n n e d to b e used in m u o n systems of new detectors for colliders at our institute. Achieved resolution is sufficient for these purposes because it is of the same order as a deflection due to multiple scattering in an absorber. In our previous work [2] it was shown that streamer tubes used here can be exploited in a drift regime providing a resolution of 130 ~m. As a result, one timing c h a n n e l allows a position resolution of 12-15 mm, a n d two timing c h a n n e l s allows a resolution of 0.13-15 m m over a detector surface of 4 0 - 1 5 0 0 0 ram.
Acknowledgements T h e authors would like to t h a n k A.E. Bondar, L.M. Kurdadze, V.P. Nagaslaev, L.V. R o m a n o v a n d B.A. Schwartz for helpful discussions, A.V. Chegodaev and Yu.A. K h o k h r j a k o v for the help in designing a n d construction of streamer tube modules, V.I. Isachenko for the help in m a n u f a c t u r i n g a n d tuning of the electronics.
References [1] S.F. Biagi, P.S.L. Booth and R.A. Donald, Delphi Internal Report 84-9 Track 1 (1984). [2] V.M. Aulchenko et al., preprint 85-122 (1985) INP Novosibirsk. [3] S.F. Biagi and P.S.L. Booth, Nucl. Inst. Meth. A252 (1986) 586. [4] B.O. Baibusinov, Graduation Thesis, Electrotechnical lnstitut of Novosibirsk (1986).
137
MUON SYSTEM BASED ON STREAMER TUBES WITH TIME-DIFFERENCE READOUT V.M. A U L C H E N K O , B.O. B A I B U S I N O V , A.G. C H I L I N G A R O V , M.Yu. L E L C H U K a n d A.B. N O M E R O T S K Y Institute of Nuclear Physics, 630090, Novosibirsk, USSR
A time-difference technique for the measurement of the coordinate along the wire has been investigated in streamer tubes connected in series. A resolution of 15 mm has been obtained for 5 tubes with a total length of 15 m. The detailed study of nonlinearity of time-coordinate relation was performed for a 8-tube chain with a total length of 10.6 m.
1.
Introduction
The study of a method of coordinate measurements along the anode wire using leading edge timing at the opposite ends of a streamer tube is presented in this paper. The possibility of streamer position measurement with an accuracy of several millimeters using this technique was tested recently [1,2]. This possibility is provided firstly by the excellent time features of streamer pulses, i.e. the short rise time, large pulse amplitude, limited dynamic range and secondly by the use of fast discriminators and advanced TDCs with a 10-20 ps resolution and small intrinsic nonlinearity. We investigated resolution, nonlinearity and calibration problems with emphasis on the series connection of tubes in a long chain (up to 15 m). This approach decreases considerably the number of readout channels and can be used in muon identifiers where the particle flow is sufficiently low. 2. Time-difference technique The time difference between the pulses arriving at the opposite ends of the tube is measured to determine the streamer position along the wire. The coordinate Z is proportional to the obtained time difference with a coefficient 1,'/2 - where V is the pulse propagation velocity in a tube. V is approximately equal to the speed of light in vacuum. Thus, the conversion coefficient T / Z is equal to 6.7 ps/mm. If compared to the charge division technique, timing has some advantages among which we mention the following: - only one digital convertor is required instead of two; an anode wire with smaller resistance and, consequently, with larger diameter can be used providing the reliable operation in the streamer mode and a simple design of streamer tubes; 0168-9002/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
the utmost attainable resolution for the time-difference technique is considerably better than for charge division [31. Both techniques were compared in detail in ref. [1,3]. The dependence of the input-output delay on the discriminator versus the form of the input signal leading edge is the most essential for the understanding of the factors governing the resolution and nonlinearity. Let us consider a conventional discriminator with a constant threshold. Then if the transmission process changes the pulse shape due to attenuation and reflections, delays on the start and stop discriminators may not compensate each other. This results in nonlinearity of a reconstructed coordinate. This nonlinearity depends on the signal amplitude. Therefore the range of pulse amplitudes degrades the resolution of the streamer position. The attenuation due to the wire resistance, in the first order of magnitude, leads to a linear addition in the time-coordinate relation and is equivalent to the reduction of the propagation velocity in the tube. The reflections, however, are essentially nonlinear factors because the reflection distorts the measured time difference only if the delay between the parent and reflected signals is less than the time between the beginning of the signal and the moment of the switching of the threshold element in the discriminator. This condition is fulfilled only in the vicinity of the tube ends. Using a series connection of tubes we inevitably insert perturbations in the transmission line. This leads to reflections and, as a result, to the linearity and resolution degradation. Hence, the investigated problem was whether the electronics used could give a sufficiently high accuracy for the series connection of a large number of tubes and how the accuracy degraded at the ends of the multitube chain where the amplitude difference between the signals arriving at the opposite discriminators was extreme. -
IV. PARTICLE IDENTIFICATION
138
V.M. Aulchenko et al. / Muon system based on streamer tubes
3. Streamer tubes
Measurements were carried out with tubes made of stainless steel with diameters of 20 and 40 mm and wall thickness of 0.2 and 0.3 mm respectively. A C u - B e anode wire with the diameter of 100 txm had a tension of 350 g. The tube ends were sealed by plastic plugs with a brass pin for a wire at the axis. Gas flowed through special inlets. Three-component gas mixtures at atmospheric pressure composed of A r - C O 2 - e t h a n o l or A r - C O 2 - n - p e n t a n e in various concentrations were used. Carbon dioxide passed before mixing through the purification system of silica aerogel and activated carbon. The series gas supply was used for several simultaneously operating tubes. In our previous work [2] the streamer mode was investigated for various gas mixtures, different cathode materials and diameters and different thicknesses of anode wire. At present the ageing effects for different anode materials are under detailed study. In tubes with a diameter of 20 mm the typical parameters of streamer pulses are as follows: a rise ime of about 3 ns, a total width of about 35 ns, an average pulse height about 3 mA, pulse height spectrum fwhm 50-70%. Operational voltage is 5200 V for A r - C O e - n pentane (l : 2 : 1) gas mixture.
4. Electronics
The electronics channel includes two front-end discriminators, a time stretcher and a direct counting T D C . The block diagram is presented in fig. 1.
The transmission line composed of several streamer tubes is terminated with a 230 ~2 resistor. This value was chosen by special optimization. The discriminators are positioned directly at the ends of the tubes and are connected to the stretcher by twisted pair cable. The signal from the time stretcher is fed into the T D C also by a twisted pair cable 20 m long. The time-coordinate calibration of the chain was made using the connections between the tubes. Duration of the stretcher output signal is proportional to the time difference between start and stop signals. The stretching coefficient is determined by the required resolution, the T D C time binning and the dynamic range. For these measurements the 12-bit T D C with the binning of 2 ns was used. With a chosen stretching coefficient of 80 the binning of the time channel was equal to 25 ps corresponding to a position resolution of 1 mm (here and below resolution means the rms deviation). The stretching is based on the charging of a capacitance by a large current followed by its discharge by a small current. The maximum stretching time difference is 120 ns. The maximum error caused by the differential and integral nonlinearities of the stretcher does not exceed 50 ps (input time). Discriminators based on the K 5 0 0 L P l l 6 integrated circuit were used. The intrinsic resolution (limited by time jitter) was measured to be 18 ps. The delay time of the discriminator depends on the pulse amplitude with a slope of about 6 p s / m V (in the region of typical amplitudes). The total thermal drift in the 2 0 - 6 0 ° C range does not exceed 15 p s / ° C. All electronics used was
i t(me
slretclter __J
.~'o~
.~eset
L--~
L ~ ~ L ~
V
,
~ ' L •
.
I;
~ATAWAY
Fig. 1. Schematic diagram of the electronics used for the time difference technique. The chain of streamer tubes is shown in the left upper corner. Calibration signals can be fed into the end of tubes.
139
V.M. A ulchenko et al. / Muon system based on streamer tubes
designed a n d built in the Institute of Nuclear Physics at Novosibirsk [4].
5. Results o | the m e a s u r e m e n t s First of all we tested the possibility of achieving high resolution for several tubes connected in series. The m e a s u r e m e n t s were carried out for tubes of 3 m length with a diameter of 40 ram. Streamer signals were produced with the help of a n 55Fe source. F o r the irradiation the tubes had special windows covered with mylar. T a b l e 1 shows the resolutions o b t a i n e d for the chains with different n u m b e r s of tubes. T h e electric c o n n e c t i o n was provided by an unshielded wire c o n d u c t o r a b o u t 10 c m long. T h e gas m i x t u r e was (20% A r - 8 0 % C O 2 ) - e t h a n o l . The operational H V was 5600 V. In the table S1 denotes the resolution in the middle of the chain; $2 is the resolution at a distance of 10 cm from the ends of the chain. Similar resolution was o b t a i n e d with the collimated
9°Sr source. H a v i n g a series c o n n e c t i o n it is c o n v e n i e n t to calibrate the tube chain in c o n n e c t i o n points. Special attention, however, should be paid to diminishing transmission line i n h o m o g e n e i t i e s causing signal reflections. W e have studied in detail the d e p e n d e n c e of the resolution versus the source position along the wire for the 4-tube chain with a total length of 4 m. The diameter of the tubes was 20 ram. The c o n n e c t i o n s between tubes were m a d e by strips of 0.3 m m width a n d a b o u t 40 m m length o n the printed circuit board. H V and calibration signals were fed into the centers of the c o n n e c t i n g strip. Fig. 2 shows the general view of the m o d u l e consisting of 12 similar tube chains put into two layers. The tubes of adjacent c h a i n s alternate with one a n o t h e r to m a k e negligible the p r o b a b i l i t y of simultaneous hitting
50 ¸
RESOLUflON, 'ram
25
Table 1 Resolution at the middle of a chain (S1) and at 10 cm from the ends ($2) for chains with different numbers of tubes Number of tubes
Length (m)
1
3
3 5
9 15
$1 (mm) 10 13 15
$2 (ram) 20 35 50
2
3
PtJ$1TION,~
Fig. 3. Resolution vs position for 4-tube chain. Hatched regions correspond to connections between the tubes. Discriminator thresholds are 10 mV. Average pulse height is about 200 mV.
Fig. 2. View of the streamer tubes module. Alternating tubes from the same layer are composed in chains with series connection. IV. PARTICLE IDENTIFICATION
V.M. Aulchenko et al. / Muon system based on streamer tubes
140
N t5 ~0 5
The large pulse height a n d the low threshold that are i m p o r t a n t for high accuracy may lead to a cross-talk, especially for the chain solution where conductors connecting the tubes are positioned close to each other. For 10 m V discriminator thresholds the pulse height causing a false hit at the adjacent c h a n n e l was found to be 350 m V in the worst case for two 8-tube chains arranged in the alternating structure m e n t i o n e d above.
6. Summary S,'mrn Fig. 4. Histogram of differences between measured and fitted positions for one of the channels. The rms deviation is equal to 10 mm that corresponds to position accuracy in a tube of 12 mm (see text).
two tubes belonging to the same chain by one particle. T h e amplitude d e g r a d a t i o n due to the a t t e n u a t i o n a n d reflections was f o u n d to be a b o u t 25% in the worst case. The d e p e n d e n c e of the measured resolution versus the posit!on is plotted in fig. 3. G a s mixture C O 2 - n - p e n t a n e (3 : 1) was used (HV 6000 V, average a m p l i t u d e 200 mV at 230 ~2). Three similar modules were tested with cosmic ray particles. Two scintillation counters 20 x 20 cm served for a trigger. The efficiency of the m o d u l e to m i n i m u m ionizing particles at H V of 6000 V was higher t h a n 99%. Six points per track were fitted with a straight fine. T h e histogram for the difference between the m e a s u r e d a n d fitted coordinate for one of the c h a n n e l s is presented in fig. 4. The rms deviation of the presented spectrum is 10 ram. This corresponds to a 12 m m resolution at one tube if one assumes equal resolution in all tubes. W i t h o u t any corrections for calibration shifts the average resolution goes up to 25 mm. T h e tube chain length in these m e a s u r e m e n t s was 4 m. Detailed study of nonlinearity was p e r f o r m e d for 8 tubes of 1.15 m length with a d i a m e t e r of 40 m m connected in series. The time-coordinate relation was o b t a i n e d with a 9°Sr source for A r - C O 2 - n - p e n t a n e ( 1 : 2 : 1 ) gas ( H V 5200 V, average a m p l i t u d e of 150 mV). The pulse height decreased b y 55% after the p r o p a g a t i o n from one end of the chain to the other. T h e m e a s u r e d points of time-coordinate relation were fitted b y a linear function with 3 parameters: the reference point, the slope, a n d the effective length of the conductor between the n e i g h b o u r i n g tubes in the chain. T h e largest nonlinearities of 40 m m were observed at the ends of the chain. T h e rms deviation from linearity over the total length of 10.6 meters is 14 mm, which is c o m p a r a b l e to the resolution.
The o b t a i n e d resolution a n d nonlinearity are in a n accordance with the values expected from the properties of the electronics used. It is clearly seen that discriminators with a lower effective threshold or discriminators with a c o n s t a n t fraction threshold could advance the position accuracy. But that requires new more sophisticated electronics design. A t present studies in b o t h directions are in progress. The investigated time difference technique is p l a n n e d to b e used in m u o n systems of new detectors for colliders at our institute. Achieved resolution is sufficient for these purposes because it is of the same order as a deflection due to multiple scattering in an absorber. In our previous work [2] it was shown that streamer tubes used here can be exploited in a drift regime providing a resolution of 130 ~m. As a result, one timing c h a n n e l allows a position resolution of 12-15 mm, a n d two timing c h a n n e l s allows a resolution of 0.13-15 m m over a detector surface of 4 0 - 1 5 0 0 0 ram.
Acknowledgements T h e authors would like to t h a n k A.E. Bondar, L.M. Kurdadze, V.P. Nagaslaev, L.V. R o m a n o v a n d B.A. Schwartz for helpful discussions, A.V. Chegodaev and Yu.A. K h o k h r j a k o v for the help in designing a n d construction of streamer tube modules, V.I. Isachenko for the help in m a n u f a c t u r i n g a n d tuning of the electronics.
References [1] S.F. Biagi, P.S.L. Booth and R.A. Donald, Delphi Internal Report 84-9 Track 1 (1984). [2] V.M. Aulchenko et al., preprint 85-122 (1985) INP Novosibirsk. [3] S.F. Biagi and P.S.L. Booth, Nucl. Inst. Meth. A252 (1986) 586. [4] B.O. Baibusinov, Graduation Thesis, Electrotechnical lnstitut of Novosibirsk (1986).