A read-out system for wire spark chambers with core memory

N U C L E A R I N S T R U M E N T S A N D M E T H O D S I o 0 (i97 z) 375-378; © N O R T H - H O L L A N D

P U B L I S H I N G CO.

A R E A D - O U T S Y S T E M FOR WIRE SPARK C H A M B E R S WITH CORE M E M O R Y F. CEVENINI

National Institute of Nuclear Physics, Naples, Italy Received 29 June 1971 and in revised form 6 December 1971 A very simple and compact read-out system for core memory spark chambers is described. It uses a multichannel analyzer as fast recording device, the reading speed is about 200000 wires/sec.

A wire spark chamber with a core memory, coupled with a read-out system capable of recording multiple events, would be an excellent device to use to measure charged particle beam profiles. Another obvious application would be the measurement of the energy spectrum of charged particles in the focal plane of a magnetic spectrometer. As is well known, the use of conventional core spark chamber systems in such cases is sometimes inadvisable because one needs very fast record systems to avoid overlong read dead times. A magnetic tape or disk storage unit or a small on-line computer are very expensive and complicated devices whose use is generally reserved to those cases in which the magnitude of the measuring problem m a k e them necessary. A record system for a spark-chamber is satisfactory when the record time is as long as the dead time of the spark-chamber high voltage pulser.Wire spark-chambers with a 10 m m or smaller gap need driving pulses up to 5 kV height and have dead times of some milliseconds. Spark-chamber core m e m o r y reading frequencies of 1 M H z or faster are easily obtainable but there is no device able to record data at such frequencies. Generally the highest read frequency obtainable from read circuits and cores is used but whenever a commutated core is found, the read cycle is stopped until after the record cycle has taken place. The dead time of the system in such cases is determined from the number o f c o m m u t a t e d cores. It is expressed from Trn = nA tl + niA t2, where n is the number of the wires, At~ is the read time, n t the number of the commutated cores and Atz, is the record time. The record time is one or two #sec for a computer central m e m o r y if one uses a modern computer and a complicated interface system, but is much longer for other recording devices. We have designed, built and tested a very compact multiple events recording system for core m e m o r y

spark chambers testing. It uses a multichannel analyzer as a multiple pulse counter. D a t a are recorded in histogram form and displayed on an oscilloscope. A multichannel analyzer is an instrument commonly found in experimental laboratories and its core memory is generally fast enough for such applications. Memory organization is displayed in fig. 1. System logic (fig. 2) is very simple. After a spark chamber event, a clock is enabled and core memory reading starts. Clock pulses increment and the address register is incremented also, and, if a m e m o r y core is commutated, the sense pulse is strobed in the multichannel m e m o r y register at the same address as that of that core. After a predetermined number of events, the circuit commands the multichannel memory print and inhibits the spark chamber and the other circuits during the print time. Our Laben multianalyzer has a memory cycle (address-register increment and memory access) of 4/~sec. We can use record frequencies of up to 200 k H z without any data damage. Therefore it is possible to use a 200 k H z read frequency without the necessity of stopping the read cycle to record. The dead time is constant and is expressed by Trn=nAt, where n is the number of wires and At is the read and record time. Since this system cannot be used for chambers with m a n y wires, because the number of memory cores cannot exceed the number of multianalyzer channels, the dead time is generally satisfactory. The oscilloscope display is a remarkable feature of this system and makes it a very versatile instrument for the testing and use of wire spark-chambers. In fig. 3 there is an histogram of the events of a hundred wires spark-chamber with cosmic rays trigger. Silver wires of 0.06 m m diameter were 3 m m spaced with a 8 m m gap. One of the three scintillation counters of the telescope was 30 m m wide and consequently sparks took place more frequently on ten of the hundred wires.

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