International audienceThis report describes the basic performance of the detector system installed in the final momentum-dispersive focal plane of the SHARAQ spectrometer

Gangnant, P.

Libin, J.F.

Michimasa, S.

Noji, S.

Ota, S.

Roussel-Chomaz, P.

Sakai, H.

Shimoura, S.

Spitaels, C.

Tokieda, H.

Uesaka, T.

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Focal Plane Detector System of SHARAQ SpectrometerS. Michimasa, H. Tokieda, S. Noji, S. Ota, S. Shimoura, T. Uesaka, H. Sakai,P. Roussel-Chomaz, J.F. Libin, P. Gangnant, et al.To cite this version:S. Michimasa, H. Tokieda, S. Noji, S. Ota, S. Shimoura, et al.. Focal Plane Detector System ofSHARAQ Spectrometer. RIKEN Accelerator Progress Report, 2010, 43, pp.174-175. <in2p3-00553112>HAL Id: in2p3-00553112http://hal.in2p3.fr/in2p3-00553112Submitted on 6 Jan 2011HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.L’archive ouverte pluridisciplinaire HAL, estdestine´e au de´poˆt et a` la diffusion de documentsscientifiques de niveau recherche, publie´s ou non,e´manant des e´tablissements d’enseignement et derecherche franc¸ais ou e´trangers, des laboratoirespublics ou prive´s.RIKEN Accel. Prog. Rep. 43 (2010)Focal Plane Detector System of SHARAQ SpectrometerS. Michimasa,� 1 H. Tokieda,� 1 S. Noji,� 2 S. Ota,� 1 S. Shimoura,� 1 T. Uesaka,� 1 H. Sakai,� 2P. Roussel-Chomaz, � 3 J-F. Libin,� 3 P. Gangnant,� 3 and C. Spitaels� 3[SHARAQ spectrometer, cathode-readout drift chamber]The consturuction of the SHARAQ spectrometer1)and the high-resolution beam line2) was completed atthe RI Beam Factory (RIBF) at RIKEN in March2009, and commissioning beam runs were performedin March and May 2009. During the beam runs, weexamined dispersion-matching ion optics and evalu-ated the performance of the detectors installed in thefocal planes of the beam line and that of the spec-trometer. Valuable information on the basic perfor-mance of the high-resolution spectrometer system wasobtained. This report describes the basic performanceof the detector system installed in the ﬁ nal momentum-dispersive focal plane of the SHARAQ spectrometer.Figure 1 shows the detector setup used in the com-missioning runs. Two tracking detectors and two plas-tic scintillators were installed in the ﬁ nal focal plane ofthe SHARAQ spectrometer. The focal plane is located3040706579BeamFocal PlaneCRDC1 SHARAQ D2 MagnetExit of D2 MagnetCRDC235oPlastic ScintillatorsAluminium WindowFig. 1. Detector setup in the ﬁ nal focal plane of SHARAQin the commissioning runs (top view). The detector sys-tem consists of two tracking detectors and two plasticscintillators.3.04 m downstream from the exit of the SHARAQD2 magnet and inclined at 35 degrees relative to thecentral orbit. The beam particles passed through thetracking detectors installed in vacuum and then passedinto the air through a 10 mm-thick aluminum window.The plastic scintillators were placed downstream of thealuminum window.The plastic scintillators were used to measure thetimings of beam particles at the focal plane and tomeasure the energy deposits in them. The two-layerconﬁ guration of the scintillators was eﬀective in re-jecting cosmic-ray events. The measured results ob-� 1 Center for Nuclear Study, University of Tokyo� 2 Department of Physics, University of Tokyo� 3 GANIL, Francetained from each scintillator were read out by two pho-tomultiplier tubes attached to the left and right of thescintillators. The size of the plastic scintillator was1110 (H) × 300 (V) × 5 (T) mm3. Charge and timingdata obtained from the scintillators were collected us-ing charge-to-time converters (QTCs)3) and multi-hitTDCs. We were able to identify 12N and 11C particleswith a separation of more than 5 σ.The tracking of particles were performed using twocathode-readout drift chambers (CRDCs)4,5). TheCRDCs have manufactured in January 2009 in collab-oration with the detector developing group of GANIL.The structure of the CRDC is described in detail inRef.5). In the commissioning runs, the CRDCs wereoperated with isobutane gas at 15 or 30 torr for thedetection of various light nuclei such as t, 6He, 9Li,12B, and 12,14N at around 200A–250A MeV.The CRDC transmits two signals from the anodewires and two multiplexed signals from the cathodepads. The anode signals were used to deduce thedrift time and the charge of secondary electrons. Thepreampliﬁ ers for the anodes were charge sensitive; theyhad a gain of 0.9 V/pC and a time constant of 20 � s.The time reference for the measurement of the drifttime was provided by the plastic scintillators. Sincethe anode signal is generated when an avalanche oc-curs around the anode wires, the drift times are de-termined by the diﬀerence between the anode timingsignal and the timing signal of the plastic scintillator.We operated CRDCs with drift electric ﬁ elds of 83.3(140) V/cm using 15-(30-)torr isobutane. The driftvelocity of the secondary electrons were 5.9 cm/� s at15 torr and 5.3 cm/� s at 30 torr, respectively. Thesevalues are approximately equal to those evaluated byusing the GARFIELD code6). Under the above men-tioned conditions, the vertical position resolution wasapproximately 0.9 mm (FWHM), which is inferior tothe design value by a factor of 2. We are continuingdata analysis in order to improve the position resolu-tion.Figure 2 shows the avalanche gain measured byCRDCs operated with 30-torr isobutane as a functionof the voltage supplied to the anode wires. CRDC1(CRDC2) corresponds to the upstream (downstream)tracking chamber in Fig. 1. The avalanche gain ofCRDC2 was consistently smaller than that of CRDC1.This diﬀerence in the gains is considered to be dueto the diﬀerence in their conﬁ gurations. In CRDC1,potential wires are placed between anode wires, whileCRDC2 has no potential wires; this has been schemati-1- 174 - cc l. ro . e .  (2010)- 175 -Fig. 2. Avalanche gain of CRDCs measured using isobu-tane gas at 30 torr. The deﬁ nitions of CRDC1 andCRDC2 are described in the text.cally depicted in Fig. 2 of Ref.5). However, we demon-strated that both the CRDCs achieved an avalanchegain higher than the required gain of 104.The detection eﬃ ciency of the CRDC is deﬃ ned hereas the ratio of the detection using the anode signalto the detection by the plastic scintillators. Figure 3shows the detection eﬃ ciency of CRDC1 as a functionof the supplied anode voltage. Fig. 3(a) shows the de-tection eﬃ ciency curves for 14N ions at 250A MeV inthe 15- and 30-torr operations, and Fig. 3(b) showsthe detector eﬃ ciency for lighter particles at around220A MeV in the 30-torr operation. It was conﬃ rmedFig. 3. (a) Detection eﬃciency for 250A-MeV 14N ions withthe 15- and 30-torr operations. (b) Detection eﬃciencyfor t, 6He, 9Li particles with the 15- and 30-torr opera-tions.that the CRDCs designed for SHARAQ will achievedetection eﬃ ciencies of approximately 100% for 200A-MeV tritons even when operated using 30-torr isobu-tane gas.The horizontal position in the focal plane is de-termined by the charge distribution on the cathodepads. The charge signals from the cathode pads wereread out by using GASSIPLEX chips7) and a CRAMSmodule8). The pedestals of the channels the GASSI-PLEX chip ranged from 60 to 70 mV and were stable(< 2 mV) over the 10-day measurements. The track-and-hold signals were generated by the timing of theanode signal of the CRDC under the condition thattwo plastic scintillators and the anode were detectedsimultaneously. In the commissioning run, we appliedanode voltages that were 30 V higher than the voltagesfor which the detection eﬃ ciencies were 100%. At thesupplied voltage, induced charges were distributed overapproximately 10 cathode pads, and the maximum in-duced charge was present around the middle of thedynamic range of GASSIPLEX. The horizontal posi-tion was deduced by ﬃ ttings of the charge distributionsto a functionq(x) = a1 · sech2 [π(x− a2)/a3] ,where ai (i = 1, 2, 3) are ﬃ tting parameters9). Thehorizontal positions corresponds to a2. The typicalresolutions of horizontal position were estimated to be500 � m and 700 � m (FWHM) for 14N at 250A-MeVand 6He at 220A-MeV, respectively.In summary, we examined the detector system in-stalled in the ﬃ nal focal plane of the SHARAQ spec-trometer in the commissioning runs of the SHARAQspectrometer by using light radioactive isotopes at200A–250A MeV. All the detectors were operated suc-cessfully and the basic data on their performance wereobtained. Identiﬃ cation of particles with atomic num-bers Z of around 7 was performed by using plasticscintillators. Under the present conditions, the posi-tion resolution of CRDCs was estimated to be 0.9 mm(FWHM) in the horizontal direction and 0.7 mm(FWHM) in the vertical direction. In the ﬃ rst exper-iment10) that was performed in November 2009, thefocal plane detector system was used, and the data onthe (t,3He) reactions at 300AMeV were obtained. Fur-ther analysis is now in progress in order to optimize thedetectors’ parameters and to improve the data-analysisalgorithm used in the detectors.References1) T. Uesaka et al.: Nucl. Instrum. Methods Phys. Res. B266, 4218 (2008).2) T. Kawabata et al.: Nucl. Instrum. Methods Phys. Res.B 266, 4201 (2008); Y. Yanagisawa et al.: Bull. Amer.Phys. Soc. 54, 48 (2009).3) H. Nishino et al.: Nucl. Instrum. Methods Phys. Res. A610, 710 (2009).4) M.H. Tanaka et al.: Nucl. Instrum. Methods Phys. Res.A 362, 521 (1995).5) S. Michimasa et al.: CNS-REP-80, (2009) 55.6) R. Veenhof, GARFIELD, CERN Program LibraryW5050.7) The GASSIPLEX is a re-designed chip of the AMPLEXby J.C. -Santiard of CERN. The AMPLEX is describedin E. Beuville et al.: Nucl. Instrum. Methods Phys. Res.A 288, 157 (1990).8) V551 C.A.E.N sequencer User Guide, V550 C.A.E.NCRAMS User Guide.9) K. Lau and J. Pyrlik: Nucl. Instrum. Methods Phys.Res. A 366, 298 (1995).10) K. Miki et al.: RIKEN Accel. Prog. Rep. 43, (2010).2- 174 - - 175 -

Focal Plane Detector System of SHARAQ Spectrometer

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Focal Plane Detector System of SHARAQ Spectrometer

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