KATANA — the Krak´ow Array for Triggering with Amplitude discrimiNAtion, has been built and used as a trigger and veto detector for the SπRIT TPC at RIKEN. Its construction allows operating in magnetic ﬁeld, providing fast response for ionizing particles and giving the approximate multiplicity and charge information on forward emitted reaction products. Depending on this information, trigger and veto signals are generated. Multi-Pixel Photon Counters were used as light sensors for plastic scintillators. Custom designed front-end and peripheral electronics will be presented as well

Brzychczyk, Janusz

Hirnyk, P.

Lasko, P.

Pawłowski, P.

Pelczar, Krzysztof

Snoch, A.

Sochocka, Anna

Sosin, Zbigniew

Łukasik, J.

Il Nuovo Cimento C

English

Brzychczyk, J.

Pelczar, K.

Sochocka, A.

Sosin, Z.

Scientific Open-access Literature Archive and Repository

DOI 10.1393/ncc/i2016-16408-5Colloquia: IWM-EC 2016IL NUOVO CIMENTO 39 C (2016) 408KATANA — a charge-sensitive trigger/veto array for the SπRITTPCP. Lasko(1)(2)(∗), J. Brzychczyk(2), P. Hirnyk, J. Lukasik(1), P. Pawlowski(1),K. Pelczar(2), A. Snoch(3), A. Sochocka(2) and Z. Sosin(2)†(1) IFJ PAN - Kraków, Poland(2) Institute of Physics, Jagiellonian University - Kraków, Poland(3) University of Wroclaw - Wroclaw, Polandreceived 10 January 2017Summary. — KATANA — the Kraków Array for Triggering with AmplitudediscrimiNAtion, has been built and used as a trigger and veto detector for the SπRITTPC at RIKEN. Its construction allows operating in magnetic field, providing fastresponse for ionizing particles and giving the approximate multiplicity and chargeinformation on forward emitted reaction products. Depending on this information,trigger and veto signals are generated. Multi-Pixel Photon Counters were usedas light sensors for plastic scintillators. Custom designed front-end and peripheralelectronics will be presented as well.1. – IntroductionThe symmetry term in the Nuclear Equation of State (NEoS) is being recently in-tensively investigated [1, 2]. The experimental efforts are focused on constraining thestiffness of the symmetry energy, especially in the range of higher densities [3]. One ofthe proposed methods consists in getting the information on momentum distribution ofcharged pions and isotopically-resolved light charged particles, Z ≤ 3, emitted in thecentral heavy-ion collisions [4-6]. Realization of this kind of measurements inspiredthe construction of the Time Projection Chamber (TPC) called SπRIT (the SAMURAIPion-Reconstruction and Ion-Tracker) [7, 8].To obtain sufficiently large gas amplification for pions and light charged particles, ahigh electric field is required inside the chamber. This brings a danger of damage whena heavier fragment passes through the chamber: charge produced by gas ionization can(∗) E-mail: pawel.lasko@ifj.edu.pl† Deceased.Creative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0) 12 P. LASKO et al.Fig. 1. – SπRIT experimental setup.exceed safe limit for the pad planes of the TPC. For this reason, a gating grid wire planewas mounted in front of the pad plane [7]. The grid is normally closed, but may bequickly opened (in ∼200 ns) when an interesting collision occurs.The KATANA array has been designed to play a double role: to produce a minimumbias or a given multiplicity trigger and to provide a veto signal whenever a beam particleor a fragment heavier than Z  20 has passed through the chamber. To fulfill therequirements, the wall has been constructed of two parts, a Veto and Trigger arrays.The KATANA-Veto part consisting of 3 thin (1 mm thick) plastic-scintillator paddleswith the middle one centered on the beam, has been designed to produce a veto signalfor heavy fragments. The KATANA-Trigger array, consisting of 12 thicker (10 mm thick)paddles, arranged on both sides of the beam, has been designed to produce a trigger.This paper will shortly describe details of the KATANA wall construction and ofthe accompanying electronics. More details on the performance of the detector will bepresented in [9, 10].2. – Experimental setupThe experimental setup [11] is depicted in fig. 1 with the SπRIT TPC as the maindetection device. The TPC was placed inside the SAMURAI super-conducting spec-trometer [12] at Rare Isotope Beam Facility (RIBF) of RIKEN [13].The target was located about 3 mm upstream of the field cage within the SπRITenclosure. The KATANA detector was located downstream of the exit TPC window.In this configuration HI beam first hits the target, than fragments pass through thechamber and finally reach KATANA paddles. An additional active collimator detectorwas applied upstream of the target to reduce the rate of the out-of-target events. Onboth sides of the TPC additional triggering KYOTO arrays were installed to provide acentral-event trigger. Neutrons were detected with the NeuLand [14] detector.KATANA — A CHARGE-SENSITIVE TRIGGER/VETO ARRAY FOR THE SπRIT TPC 3Fig. 2. – KATANA detector: a technical drawing with external dimensions (in mm).3. – KATANA detector — overall descriptionThe design of KATANA detector is schematically presented in fig. 2. Three vetoplastic bars, marked with dashed lines, (size 400 × 100 × 1mm3, made of BC404) areplaced in about the middle of the frame. Twelve trigger plastics (400 × 100 × 10mm3,made of BC408) are placed unevenly on both sides of the beam (7 on the left and 5 onthe right side) to account for bending of the charged particles in the magnetic field.The scintillators are fixed to the frame by two handles. For the thick paddles thelight is collected by two light sensors, each located in the middle of the top and bottomside of the plastic. The light is read out directly, without any light-guides. The handlesfor the thin veto paddles have more complex design (see fig. 3). Here, the light is readout by four light sensors. First the light is collected along the plastic edge with theuse of a Wave Length Shifter (WLS) fiber (type BCF92). The WLS collects light fromshorter sides of the scintillator and propagates it to the light sensors mounted on bothsides of the fiber. In both cases, the Multi Pixel Photon Counter (MPPC) devices fromHamamatsu [15] have been used as the light sensors.Figure 3 shows a conceptual design of a single veto module. It is worth mentioningthat each MPPC is mounted directly on a preamplifier PCB to minimize the noise level.The front-end electronics is completed by analog adders, each providing analog sum ofsignals coming from all sensors of a single paddle. Thus, each paddle provides finally asingle electric pulse. Analog adders provide an inverted signal as well.The frame of KATANA detector is mounted on two trolleys, capable to move onspecial rails used primarily to set-up the position of the SπRIT TPC inside the SAMURAIa) b)Fig. 3. – a) KATANA single veto module; b) Veto scintillator handle.4 P. LASKO et al.Fig. 4. – KATANA signal wiring.vacuum chamber. Trolleys provide also possibility for left-right adjustment of the frame(see fig. 2).4. – Signal path descriptionFigure 4 shows the distribution of the signal wires. The amplified MPPC’s signalsof each plastic scintillator are summed, providing one analog signal per each scintillator.Each analog adder has normal and inverted output. In total KATANA provides 15normal (positive) signals and 15 inverted (negative) ones.The positive signals are sent to a Flash ADC board (CAEN V1730) for control pur-pose. The negative signals are dispatched to the leading edge discriminators and arecompared to the threshold levels set by remotely controlled DAC cards. The logic out-puts of discriminators are then analyzed by a logic circuit built on a FPGA board. TheFPGA circuit takes into account discriminated signals from all KATANA paddles (trig-ger and veto) and additionally, the signals from the Active Collimator and the majoritylogic signal from the KYOTO array. Its fast and flexible logic allows to provide quickly(within <100 ns) the signals required by the TPC gating grid and by the acquisitionsystem.5. – Electronics description5.1. MPPC sensors. – The light readout has been done using the MPPCs of twotypes. For the thick paddles the S12572-025 product was used. Its photo-sensitive areaof size 3×3mm2 consists of 14400 pixels-separate avalanche diodes. The thin paddles areread out by the S12571-010 element, containing 10000 pixels on 1 × 1mm2 area. Mainparameters of the applied MPPCs are specified in table I.5.2. Preamplifier for MPPC . – A schematic of the preamplifier applied is shown infig. 5. It consists of a few basic blocks: a common base and a common collector (emitterfollower) amplifiers based on the T1 and T2 transistors, respectively; and a simple polezero cancellation circuit based on the C3, R7 and R8 elements.KATANA — A CHARGE-SENSITIVE TRIGGER/VETO ARRAY FOR THE SπRIT TPC 5Table I. – Main parameters of the applied MPPCs.S12571-010 S12572-025Photosensitive area 1 × 1 mm 3 × 3 mmNumber of pixels 10000 14400Typical operating voltage 69 V 68 VGain 1.35 × 105 5.15 × 105Peak sensitivity WL 470 nm 450 nmGain temp. coefficient 1.6 × 103/ K 8.2 × 103/ KPhoton detection efficiency 10% 35%The low-voltage power supplies and filters are omitted in the schematic but it isobvious that high stability and low-noise power supply is required.The MPPC (D1) is polarized by sufficiently high voltage (HV) provided by high-voltage power supply described below. High frequency signal pulses are passing throughC1 to low impedance input of the common base amplifier. This kind of an amplifier waschosen because of its good characteristics for high frequency operation.A common collector amplifier was used to match the output impedance. The R6 andR9 resistors also play a significant role in this respect. The C2 capacitor cuts off the DCcomponent.The preamplifier allowed to achieve a one-photon resolution in amplitude. Figure 6shows the amplitude distribution obtained from a thick paddle, stored in a dark room.The peaks correspond to one, two and more photon, events. It clearly shows sensitivityand amplitude resolution of the thick (trigger) paddles. Of course, during the experiment,the thresholds were set-up much above this natural noise, to detect only light chargedparticles. On the other hand, the sensitivity of thin (veto) paddles is much lower, as itshould give response only for heavy charged fragments.5.3. HV supply . – The MPPC elements need to be biased. This goal was achievedby designing a dedicated HV power supply, satisfying the following special requirements:10 mV precision, low noise and low voltage ripple (< 1mV), 60–80 V range of regulation,40 channels, remote control via Ethernet, multi-point temperature control, current limiterand a feedback info (saturation/error).Fig. 5. – Schematic of the preamplifier for MPPC.6 P. LASKO et al.Fig. 6. – Single-photon amplitude resolution achieved for thick paddles, equipped with S12572-025 elements.Figure 7 presents an actual view of the high voltage power supply (note its modular,expandable construction).The HV supplier was remotely controlled. The controller was based on a STM32F103microcontroller with ARM Cortex-M3 core. The Ethernet controller allowed to createa system working in a server mode. The IP and port numbers for the communicationare configurable. The interface for the DAC cards and HV cards was custom designedand allowed to connect those cards in parallel. Each card is provided with switches forsetting the card address.The HV supply is temperature sensitive. A DS18B20 element has been chosen asa built-in temperature sensor. This is a digital thermometer with 12-bit (0.0625 ◦C)resolution and 1-Wire interface for communication. Two such devices were installedinside the high voltage power supply box. Additionally, six such sensors were mountedon the frame of the KATANA detector to monitor the operating temperature of theMPPCs. The temperature data were collected by the controller and were available uponrequest from the server.The HV modules on the HV pwr card (see fig. 7) can be turned on/off separatelya) b)Fig. 7. – HV power supply for the MPPC: a) picture of the device; b) block diagram.KATANA — A CHARGE-SENSITIVE TRIGGER/VETO ARRAY FOR THE SπRIT TPC 7through the controller. Before switching on, the controller sends a code to the specifiedDAC corresponding to the required voltage. The voltage on the DAC output is a referencevoltage for the HV module: the required high voltage appears on the HV module output.The HV module is based on a MAX1932 APD bias supply and has a flexible design:it can work in analog mode (as described above) or in a “stand alone” mode. In thelatter mode a built-in DAC is in use. Nevertheless, our construction is based on externalDACs to achieve better parameters. Additional filters were applied as well.The device is fully controlled through Ethernet and all information about its statecan be read out.SummaryIn summary, we have presented technical details of the KATANA detector. The detec-tor was built, tested and used in the recent experiment at RIKEN, playing a significantrole in the detection system. Its construction allowed to place it inside strong magneticfield just behind the SπRIT TPC exit window. Fast response, high triggering efficiency,insensitivity to magnetic field, stability and the possibility of remote control were themain attributes of this trigger and veto array.∗ ∗ ∗Work supported by Polish National Science Center (NCN), Contract Nos. UMO-2013/10/M/ST2/00624 and UMO-2013/09/B/ST2/04064.REFERENCES[1] Tsang M. B. et al., Phys. Rev. C, 86 (2012) 015803.[2] Li B.-A. and Han X., Phys. Lett. B, 727 (2013) 276.[3] Russotto P. et al., Phys. Lett. B, 697 (2011) 471; Phys. Rev. C, 94 (2016) 034608.[4] Li B.-A., Phys. Rev. Lett., 88 (2002) 192701.[5] Rizzo J. et al., Phys. Rev. C, 72 (2005) 064609.[6] Hong J. and Danielewicz P., Phys. Rev. C, 90 (2014) 024605.[7] Shane R. et al., Nucl. Instrum. Methods A, 784 (2015) 513.[8] Jhang G. et al., J. Korean Phys. Soc., 69 (2016) 144.[9] Lasko P. et al., in preparation, arXiv:1610.06682.[10] Lasko P. et al., Proceedings of the 2016 Zakopane Conference on Nuclear Physics, to bepublished in Acta Phys. Pol. B.[11] groups.nscl.msu.edu/hira/NP1306 SAMURAI15/index.htm.[12] Kobayashi T. et al., Nucl. Instrum. Methods B, 317 (2013) 294.[13] Yano Y. et al., Nucl. Instrum. Methods B, 261 (2007) 1009.[14] www.gsi.de/en/work/project management fair/rare isotope beams/r3b/neuland.htm.[15] www.hamamatsu.com .

KATANA — a charge-sensitive trigger/veto array for the SπRIT TPC

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