Camarri, P

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29th International Cosmic Ray Conference Pune (2005) 8, 8992Control and monitoring of the ARGO-YBJ detectorP. Camarri , R. Cardarelli and Q. Goufor the ARGO-YBJ collaboration(a) INFN Section of Rome 2 and Physics Department of the University of Roma Tor Vergata, Italy(b) IHEP Beijing, ChinaPresenter: P. Camarri (Paolo.Camarri@roma2.infn.it), ita-camarri-P-abs1-he15-oralThe ARGO-YBJ Detector Control System (DCS) is designed to control and monitor the most significant oper-ational parameters of the experiment, related both to the detector and to the environment. Beyond monitoringthe stability and the reliability of the detector operation, the DCS is also sensitive to sudden current changes inthe RPCs, induced by high density air showers. The control procedures are described, and the dependence ofthe RPC currents on the environmental parameters is presented.1. IntroductionThe Detector Control System (DCS) of the ARGO-YBJ experiment [1] was described in [2], where its mainarchitectural and operational features were presented. At present (June 2005), 42 clusters (about 1/3 of thecentral carpet) have been installed, 16 of which have been operated and monitored for more than one year. Themain purpose of the DCS is to guarantee the overall reliability and robustness of the system by controlling thehigh-voltage power supplies and monitoring the time trends of all the significant operational and environmentalparameters. The ARGO-YBJ detector is a full-coverage array of Resistive Plate Chambers (RPC) [3] operatedin streamer mode. The operating voltage is chosen so that the actual single-hit time resolution is about 1 ns.Continuous monitoring of the single RPC absorption current is crucial to guarantee the stability of the efficiencyof every chamber and to check that the gas flow through each RPC is regular. In addition, constant monitoringmay provide important support to the data analysis, mainly concerning sudden changes in the air-shower rateif an increase lasting longer than a few seconds is observed.2. Details of the DCS implementationThe RPC high-voltage channels are powered by CAEN SY127 mainframes, which are controlled using a PCinterface (CAEN A1303 PCI board) and a dedicated program developed in the LabVIEW environment [4].This is meant to control the applied voltage and monitor both the output voltage and the absorption currenton each high-voltage channel continuously. The single RPC absorption currents, the voltage powering theRPC electronics front-end boards and the local temperature are collected by a suitably designed multiplexerboard on each cluster and recorded by a VME acquisition system, which also records the barometric pressuremeasured by a sensor placed in the center of the experimental hall.A three-component gas mixture is used for the RPC operation, namely C  H  F  /Ar/i-C  H  = 75/15/10. Afourth, strongly electronegative component, SF  , will soon be added (with an overall concentration of a fewper mil) in order to reduce the average streamer charge and therefore to increase the detector robustness byreducing one of its ageing factors. The gas mixture sent to the detector is monitored continuously usingmass flowmeters with adequate accuracy. Moreover, the amount of residual gas in each bottle is checked bymeasuring the pressure for the Argon and the weights of the bottles containing the other gas components, whichare compressed liquids inside the bottles.To check the correct behavior of the RPC detectors, it is also necessary to monitor the count rates for each RPCchamber. This feature is about to be implemented in the DCS. The count rate of each RPC is provided by the90 P. Camarri, R. Cardarelli and Q. Goufast logical OR of 10 pads, each one corresponding to 	 of the active detector area. The fast OR is providedby the local trigger station [5] and translated into differential TTL signals. The count rates are recorded by PXIFPGA boards, each one implementing over 100 count-rate channels.3. Alarms and warningsThe DCS of the ARGO-YBJ experiment is designed to monitor the following quantities:1. the gap currents for each RPC, the voltage powering the RPC front-end electronics and receiver boards,the local temperature on each cluster and the barometric pressure in the experimental hall: these param-eters are sampled every few seconds;2. the applied voltage and the absorption current in every high-voltage channel;3. the gas pressure for the Argon line and the bottle weights for the liquid gas bottles.Beyond monitoring the correct operation of the detector, the DCS must provide a prompt and reliable feedbackevery time some anomalous behavior is detected. The most important occurrences for alarms, warnings andfeedbacks are the following:1. High-current alarm. This is issued whenever a chamber absorption current becomes higher than a safelyestablished upper limit, e.g. 7  A. In order to avoid potential damages to the chambers due to highcurrent, the DCS starts a protection procedure by switching off the corresponding high-voltage channel.2. Working-point stabilization. Changes in the barometric pressure and in the local temperature affect thedensity of the gas mixture, causing the RPC working point to change. In order to keep the workingpoint stable, the applied voltage must be constantly updated according to the relationship 		 , where  is the voltage to be applied at absolute temperature  and barometric pressure  ifthe operating voltage is ﬀ at reference temperature ﬁ and barometric pressure  . This feedback willsoon be introduced.3. Low voltage alarm. This is issued whenever the low voltage powering the RPC electronics front-endboards has wrong values.4. Empty-bottle alarm. This is issued whenever the Ar gas pressure becomes too low or the weights ofthe C  H  F  and iC  H   bottles drop below a fixed lower threshold, implying that some of the gascomponents are about to be exhausted.4. Continuous monitoring of the detectorThe ARGO-YBJ DCS has been monitoring the first 16 clusters of the experimental setup for over one year.The time trends of the monitored parameters are crucial to check the correct behavior of the detector.In Fig. 1 the time trend of the total gap current for the 16 RPC clusters (monitored every 6.5 seconds for over3.5 hours) is shown. Sudden high spikes due to the detection of dense air showers are evident.In Fig. 2 the time trend (for 13 days in August, 2004) of the average total gap current is shown. The dailychanges related to the time trends of both the barometric pressure and the temperature inside the experimen-tal hall are clearly seen. The trends of the pressure and the inner temperature over the same time span areControl and monitoring of the ARGO-YBJ detector 9165070075080085090095010002004/08/1522:04:482004/08/1522:33:362004/08/1523:02:242004/08/1523:31:122004/08/160:00:002004/08/160:28:482004/08/160:57:362004/08/161:26:242004/08/161:55:122004/08/162:24:00I 16 ( µµ µµA)Figure 1. Time trend of the total gap current for 16 RPCclusters. The sampling time is 6.5 s. The plot refers to a3.5-hour observation time. The spikes due to the detectionof dense air showers are clearly seen.6506706907107307507707908108308502004/08/09 0:00 2004/08/11 0:00 2004/08/13 0:00 2004/08/15 0:00 2004/08/17 0:00 2004/08/19 0:00 2004/08/21 0:00I 16 ( µµ µµA)Figure 2. Time trend of the total gap current for 16 RPCclusters, averaged every 130 s, during a 13-day span in Au-gust 2004. Each point is the average of 20 measured values.respectively shown in Fig. 3 and 4, where the typical daily trends of the two environmental parameters areseen.These trends are crucial to correlate the RPC gap current with the local temperature at constant pressure, andwith the barometric pressure at constant temperature. Examples of this type of analysis are shown in Fig. 5and 6, where linear fits to the experimental points are also added. In the chosen conditions, the estimateddifferential changes of the gap current are about 3% / ﬂ C and -2% / mbar respectively.5. ConclusionsThe DCS of the ARGO-YBJ experiment provides continuous monitoring and control of all the relevant param-eters which affect the detector operation. Its support to the data analysis will be increased very soon with theaddition of the single RPC count-rate monitoring system.References[1] B. D’Ettorre Piazzoli et al.(ARGO-YBJ Coll.); 29th ICRC, Pune (2005), OG.2.7 .[2] P. Camarri et al. (for the ARGO-YBJ Coll); 28th ICRC, Tuskuba (2003), 761.[3] R. Santonico and R. Cardarelli; Nucl. Instr. and Meth. A 377 (1981), 187.R. Cardarelli and R. Santonico; Nucl. Instr. and Meth. A 263 (1988), 200.[4] National Instruments; “LabVIEW User Manual”, April 2003 (PN 320999E-01).[5] G. Marsella et al. (for the ARGO-YBJ Coll); Nucl. Instr. and Meth. A 518 (2004), 549.92 P. Camarri, R. Cardarelli and Q. Gou6036046056066076086096106112004/08/090.00.002004/08/110.00.002004/08/130.00.002004/08/150.00.002004/08/170.00.002004/08/190.00.002004/08/210.00.00Barometric pressure (mbar)Figure 3. Time trend of the barometric pressure, averagedevery 130 s, during a 13-day span in August 2004. Eachpoint is the average of 20 measured values.15161718192021222004/08/090.00.002004/08/110.00.002004/08/130.00.002004/08/150.00.002004/08/170.00.002004/08/190.00.002004/08/210.00.00Inner temperature (°C)Figure 4. Time trend of the temperature inside the ARGO-YBJ experimental hall, averaged every 130 s, during a 13-day span in August 2004. Each point is the average of 20measured values.I16 (µA) = 19.6 t (°C) + 37970071072073074075076077016.5 17 17.5 18 18.5 19 19.5 20Temperature (°C)I 16 ( µµ µµA)p = 608.8 mbarFigure 5. Correlation plot of the total current on 16 clustersversus the experimental hall inner temperature, both aver-aged every 130 s, at constant barometric pressure (608.8mbar).I16 (µA) = -17.42 p(mbar) + 11378780790800810820830840850604.5 605 605.5 606 606.5 607 607.5 608Barometric pressure (mbar)I 16 ( µµ µµA)t = 20.3 °CFigure 6. Correlation plot of the total current on 16 clustersversus the barometric pressure, both averaged every 130 s,at constant inner temperature (20.3 ﬃ C).

Control and monitoring of the ARGO-YBJ detector

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