Status of the vertex detector program of the CBM experiment at FAIR
Philipp Klaus, Michal Koziel, Ole Artz, Norbert Bialas, Michael Deveaux, Ingo Fröhlich, Jan Michel, Christian Müntz, Roland Weirich, Joachim Stroth
aa r X i v : . [ phy s i c s . i n s - d e t ] O c t Status of the vertex detector program of the CBMexperiment at FAIR
Philipp Klaus ∗ , Michal Koziel, Ole Artz, Norbert Bialas, Michael Deveaux,Ingo Fr¨ohlich, Jan Michel, Christian M¨untz, Roland Weirich, Joachim Stroth Goethe-Universit¨at Frankfurt, Institut f¨ur Kernphysik, Max-von-Laue Strasse 1, 60438Frankfurt am Main, Germany.
Abstract
The Compressed Baryonic Matter Experiment (CBM) is one of the core ex-periments of the future FAIR facility (Darmstadt/Germany). The fixed-targetexperiment will explore the phase diagram of strongly interacting matter inthe regime of high net baryon densities with numerous rare probes. The Mi-cro Vertex Detector (MVD) will determine the secondary decay vertex of opencharm particles with ∼ µ m precision, contribute to the background rejectionin dielectron spectroscopy, and help to reconstruct neutral decay products ofstrange particles by means of missing mass identification. The MVD comprisesfour stations with 0.3 and 0 . x/X , which are placed between 5 and 20 cmdownstream the target and inside vacuum. It will host highly-granular, next-generation Monolithic Active Pixel Sensors, with a spatial precision of 5 µ m, atime resolution of 5 µ s, and a peak rate capability of ∼
700 kHz / mm . Moreover,a tolerance to 3 · n eq / cm and & Keywords:
Solid State Detectors - Poster Session; Vertex Detector; CBM;Integration; CMOS Pixel Sensors
1. Introduction
The MVD of the fixed target Compressed Baryonic Matter Experiment [1]will consist of four CMOS pixel detector stations [2] populated with radiation-tolerant sensors, form-factor 31 ×
17 mm , thinned to 50 µm. An ultra-lightand vacuum-compatible cooling concept is foreseen to transfer the dissipatedpower of the sensors via highly heat-conductive carriers (CVD-diamond [3] andThermal Pyrolytic Graphite [4]), in turn clamped into liquid cooled aluminum-based heat sinks mounted outside the detector acceptance. Control, power, and ∗ Corresponding author: Philipp Klaus
Email address: [email protected] (Philipp Klaus)
Preprint submitted to Elsevier October 23, 2018 ata links are provided to the sensors via customized, thin Flexible PrintedCircuit (FPC) cables. The sensors exposed to the maximum hit densities willbe read out by the mean of eight differential data links. This paper summarizesthe status of sensor development, station prototyping, and detector slow control.
2. Sensor Development
Figure 1: Visualization of the Micro-Vertex Detector of the CBM experiment. Station three isfully depicted. It employs nine sensors on one side and six on the other side, respectively. TheTPG carrier is clamped into an aluminum heat sink that holds also passive R/O electronics(DC filters and impedance matching).
There is no ready technical solution that could provide a CMOS Pixel Sen-sor (CPS) suitable for the CBM experiment, e.g. the ALICE-ALPIDE chip [5]is not adapted to the maximum hit rate and radiation load at CBM (drivenby local hot-spots due to δ -electrons in the fixed-target setup). The CBM-MVD sensor, called ”MIMOSIS”, is being developed by IPHC Strasbourg withthe TowerJazz 0.18 micrometer process, same as used for manufacturing theALPIDE chip. MIMOSIS will profit of ALPIDE’s readout but feature an in-pixel architecture more tolerant to radiation and will be equipped with entirelynew digital micro-circuitry (chip communication, signal processing and control).The sensor development is made in several steps, where the first is realized witha prototype chip called MIMOSIS-0, aiming at selecting an optimum in-pixelarchitecture and studying the built-in priority encoder. To characterize the sen-sor performance, a dedicated readout system that provides sensor powering anddata transmission from the sensor to the computer, has been developed. Tospeed up test campaign, several test benches were set up and distributed withinthe participating institutes. The planned radiation tolerance tests will coverthe doses up to 10 Mrad and 10 n eq / cm . We focus on selecting the most ro-bust in-pixel architecture and characterizing, after irradiation, the performanceof digital to analog converters used to define reference voltages and operatingpoints for, e.g. in-pixel amplifiers and discriminators.2 . Prototyping There were two prototyping phases accomplished validating the feasibilityof use the CVD diamond and TPG materials as a carrier capable to most ef-ficiently transfer the heat from the MVD sensors. The prototype described in[6] was based on the CVD-diamond and hosting two 50 µm-thin MIMOSA-26sensors [7, 8] on both sides of the CVD carrier. The second prototype, called”PRESTO” [9], comprises 15 thinned CPS of the same type. Nine of the sen-sors were glued on the front, and six on the back side of the module. Figure1 illustrates the full detector and PRESTO. The sensors are wire bonded to atotal of 10 FPC cables, which provide the necessary bias lines and data links.PRESTO has the size of a quadrant of the 2nd MVD station but due to thenumber of sensors integrated, its complexity is equivalent to the one of the 3rdstation. The assembly procedures and QA measures were established, guaran-teeing vacuum compatible integration of the sensors on both sides of the carrierwith a placing precision of better than 100 µm. Cooling concept, selection ofadhesives, vacuum compatibility, and FPC cable performance [10] were studiedwith a positive outcome. The rather poor sensor assembly yield of ∼
60% forthe PRESTO module was identified as problems with a wire bonding machine.This will be proven by a follow-up prototype.
4. Detector Slow Control
For 24/7 reliability tests of the PRESTO module and to ensure a failsafeoperation of the device at any time, the EPICS framework (v3.15.5) [11] isused to monitor and control the system. We have implemented the requiredI/O Controllers (IOCs), those are the EPICS server processes that establish theconnection between the laboratory equipment and the EPICS network calledchannel access (CA). The CS-Studio RDB Archiver was chosen to store processvariables in a PostgreSQL database set up with table partitioning, see [12].What concerns the user interfaces, a two-fold strategy was selected: A CS-Studio interface was created for full-fledged system control, locally accessiblefor the operators and experts. In addition, a highly configurable web dashboardfor EPICS PVs was developed. Running in any modern browser, it can beused on any device with an internet connection. It was designed to be r/o. Incase user logins and protocolling would be added later, write acces could beconsidered. At the moment, we are implementing cross-IOC alarm handlingand procedures to startup / shutdown the detector. This work serves also as asmall size prototype of the CBM-MVD slow control system.
Acknowledgments
We would like to thank the IPHC-PICSEL team for their work. Work sup-ported by BMBF (05P15RFFC1), HIC for FAIR and GSI.3 eferences [1] V. Friese, ”The CBM experiment at GSI/FAIR”, Nuclear Physics A 774(2006) 377.[2] R. Turchetta et al., ”A monolithic active pixel sensor for charged particletracking and imaging using standard VLSI CMOS technology”, Nucl. Instr.and Meth. A 458 (2001) 677.[3] Diamond Materials GmbH., .[4] Momentive Performance Materials, Inc., .[5] G. Aglieri Rinella, ”The ALPIDE pixel sensor chip for the upgrade of theALICE Inner Tracking System”, Nucl. Instr. and Meth. A 845 (2017) 583.[6] M. Koziel at al., ”The prototype of the Micro Vertex Detector of the CBMExperiment”, Nucl. Instr. and Meth. A 732 (2013) 515.[7] C. Hu-Guo et al., ”First reticule size MAPS with digital output and in-tegrated zero suppression for the EUDET-JRA1 beam telescope”, Nucl.Instr. and Meth. A 623 (2010) 480.[8] A. Dorokhov et al., ”High resistivity CMOS pixel sensors and their appli-cation to the STAR PXL detector”, Nucl. Instr. and Meth. A 650 (2011),174.[9] M. Koziel at al., ”Vacuum-compatible, ultra-low material budget Micro-Vertex Detector of the compressed baryonic matter experiment at FAIR”,Nucl. Instr. and Meth. A 845 (2017) 110.[10] P. Klaus at al., ”Prototyping the read-out chain of the CBM MicrovertexDetector”, JINST, Vol.11/03, pp. 03046, 2016.[11] Experimental Physics and Industrial Control System, https://epics.anl.govhttps://epics.anl.gov