Chlad, L.

Koenig, W.

Pietraszko, J.

Rost, A.

GSI Repository

Optimizing the PaDiWa-AMPS TDC and QDC front-end electronics for theHADES pion beam Hodoscope∗A. Rost†1, L. Chlad2, W. Koenig3, and J.Pietraszko3 for the HADES Collaboration1TU Darmstadt, Darmstadt, Germany; 2Nuclear Physics Institute of ASCR, Rez, Czech Republic; 3GSI, Darmstadt,GermanyThe HADES pion beam experiment has started to takedata in summer 2014. A dedicated tracking system CER-BEROS [1] and a Start detector have been used to mea-sure the momentum, the position and precise time of thepions in front of the spectrometer. A Hodoscope was lo-cated behind the spectrometer and was used as an addi-tional beam position monitor detector. The Hodoscope [2]is built from 16 plastic scintillator rods with the dimensionsof 10x5x100 mm, aligned horizontally. The scintillationsignal of the rods is read out on each side by HamamatsuR3478 photo-multiplier tubes (PMTs) providing to get hor-izontal position information.Fast TDC and QDC with online monitoring in real-timewere needed to control the direction of the pion beam inthe spectrometer. The PaDiWa-AMPS front-end board forthe TRBv3 [3] was used to measure the time and the chargeinformation of the PMT signals. The TDC is implementedin an FPGA by the tapped delay method. A high precisioncharge measurement is achieved by implementing a modi-fied Wilkinson-ADC method, so that actively dischargingof the integrated signal results in a fast crossing of thethreshold. The width of the pulses, which are proportionalto the charge, are measured by the well-established TRBv3platform. Because it is realized based on the KISS (Keepit Small and Simple) principle, it is possible to modify thefront-end electronics with little effort and adapt it to differ-ent PMT signal shapes. The first version of the PaDiWa-AMPS front-end electronics was optimized for HADESECAL PMTs and was already successfully tested underbeam conditions [4].In Fig. 1 (left) a Hodoscope PMT signal is shown. Incomparison, HADES ECAL PMT pulse-shapes have anamplitude of about 1 V and a pulse-width of about 50 ns.An adaption to the smaller and shorter Hodoscope signalswas needed. By modifying the input attenuation of thePaDiWa-AMPS front-end board and by reducing the inte-gration time by an FPGA design update, a significant im-provement in the signal-to-noise ratio and in the rate ca-pability has been achieved. In Fig. 1 (right) the chargemeasurement of the Hodoscope version is shown.By subtracting the measured time information of theStart detector t0 from the Hodoscope t1 and with the as-sumption σ2 ≅ σ2Hodo + σ2Start a time measurement pre-cision of the Hodoscope and the Start detector could beestimated. After time-walk corrections and for events withthe pion beam aligned in the central part of both detectors a∗Work supported by VH-NG-823, HA216/EMMI, HIC for FAIR, GSI.† a.rost@gsi.detime resolution of σHodo ≅ σStart ≅ σFit√2 = 196 ps couldbe achieved (see Fig. 2).Figure 1: PMT pulse-shape of the Hodoscope (left). Themeasured charge encoded in the width of the integrated andlinearly discharged signal (right).Figure 2: Time difference between Hodoscope and Startdetector after time-walk corrections and for events withpion beam aligned in the central part of both detectors.References[1] L. Fabbietti et al., “Integration of the Pion-Beam Tracker intothe HADES DAQ”, GSI Scientific Report 2013[2] J. Diaz et al., “Design and commissioning of the GSI pionbeam”, Nucl.Instrum.Meth., 2002, Volume 478, Issue 3, p.511-526[3] M. Traxler et al., “A Precise Multi-Channel QDC FEE uti-lizing FPGAs as Discriminators and Delay Elements Basedon the TRB3 as TDC and Readout Platform”, GSI ScientificReport 2013[4] O. Svoboda et al., “Test of the HADES ElectromagneticCalorimeter modules on photon beam”, GSI Scientific Report2013MU-NQM-HADES-25 GSI SCIENTIFIC REPORT 201428 DOI:10.15120/GR-2015-1-MU-NQM-HADES-25

Optimizing the PaDiWa-AMPS TDC and QDC font-end electronics for the HADES pion beam Hodoscope

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Optimizing the PaDiWa-AMPS TDC and QDC font-end electronics for the HADES pion beam Hodoscope

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