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12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3

IBIC2023, Saskatoon, Canada
JACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - M O P 0 1 8BEAM-DIAGNOSTIC AND T0 SYSTEM FOR THE mCBM AND CBMEXPERIMENTS AT GSI AND FAIR
A. Rost1∗ , T. Galatyuk2,3 , V. Kedych3 , M. Kis2 , W. Krüger3 ,J. Pietraszko2 , A. Senger1 , J. Thaufelder2 , F. Ulrich-Pur2
1
FAIR GmbH, Darmstadt, Germany
2
GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany
3Institut für Kernphysik, TU Darmstadt, Darmstadt, Germany
Abstract

Table 1: Requirements to the CBM BMON System

The Compressed Baryonic Matter (CBM) experimentat the Facility for Antiproton and Ion Research (FAIR) inDarmstadt requires a highly accurate beam monitoring andtime-zero (T0) system. This system needs to meet the requirements of the CBM time-of-flight (ToF) measurement
system for both proton and heavy ion beams, while also
serving as part of the fast beam abort system. To achievethese goals, a detector based on chemical vapor deposition(CVD) diamond technology has been proposed. In addition,
new developments using Low Gain Avalanche Detectors(LGADs) are currently under evaluation. This contribution
presents the current development status of the beam detector
concept for the CBM experiment.

Max. beam intensity
Max. read-out rate
Time precision
Position resolution
Beam spot size on sensor
Sensor thickness

107 particles/s on sensor
5 MHz per channel
50 ps
0.5 mm
1 cm (2 sigma)
70 µm

will be used for beam halo monitoring and as a port of a fast
beam abort system (BAS). Both detectors will be mounted
inside a beam-pipe using commercially available CF 100
vacuum elements, as schematically shown in Fig. 1.

INTRODUCTION
The CBM experiment [1] is a fixed-target, multi-purpose
detector that will be used to explore the QCD phase diagramof nuclear matter at high net-baryon densities and moderatetemperatures. The experiment will be located at the Facility for Antiproton and Ion Research (FAIR) in Darmstadt,Germany.
The CBM detector will be able to detect hadrons, photons,electrons, and muons in elementary and heavy-ion collisions
over the entire energy range provided by the SIS100 heavyion synchrotron, from 3 to 11 A GeV for heavy ions and29 GeV for protons. The measurements will be performed at
event rates from 100 kHz up to 10 MHz using free-streaming
readout electronics and fast online event reconstruction.
The BMON system consists of a high-speed timezero (T0) and halo detector. The detector must meet therequirements of the time-of-flight (ToF) measurement system for both proton and heavy-ion beams. Specifically, it
must achieve a time precision better than 50 ps (sigma), maintain stable long-term operation even at high interaction ratesof 107 particles/s, and have a detection efficiency approaching 100%. A summary of the requirements is provided inTable 1.

THE CBM BEAM MONITORING SYSTEMThe CBM BMON system has been already introducedin [2], it will consist of two detector stations located in frontof the CBM target chamber. The T0-station is foreseen tomeasure the start time of the reaction, while the Halo-station∗ a.rost@gsi.deFigure 1: The CBM BMON system consists of two stations for beam halo and T0 measurement. The stations aremounted in standard CF 100 vacuum chambers in front ofthe CBM target. The T0 station uses a single sensor, while
the Halo station uses a mosaic structure of four sensors.
The Halo station will also be part of a fast beam abort system (BAS).
The sensor for the T0 station is currently planned to bemade using poly-crystal CVD (pcCVD) diamond technology [3]. The sensor will have a thickness of 70 µm and will
cover an area of 1 × 1 cm2 . It will be equipped with a metallization arranged in 16 strips on each side. A detailed
description of the sensor and the production and testingof a prototype sensor can be found in [2]. The strip segmentation and orientation, aligned in the 𝑥 and 𝑦-directions,will allow to extract the position information of the beam
particles. We are currently also investigating higher segmen-MOP01866

02 Beam Position Monitors

IBIC2023, Saskatoon, Canada
JACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - M O P 0 1 8tation, i.e. 48x48 strips, for the final CBM T0 sensor. This
will increase the rate capability of the sensor.
The halo station is planned to be used as an independent
beam monitoring system. The halo detector will consistof a mosaic arrangement of four sensors, each metallizedwith four strips on both sides. The sensor arrangement is
schematically shown in Fig. 1. This arrangement allows tomonitor the beam position and its rate during the extraction
process. This information will be used to secure sensitive
CBM detectors as part of a fast beam-abort system (BAS).
At the moment, we are actively investigating the possibility of using recently developed Low Gain Avalanche Detector (LGAD) technology, especially for proton beams in theCBM experiment. LGAD technology has been shown to bevery promising for beam monitoring applications, as it canachieve high time resolution and rate capability [4].

INFLUENCE OF THE T0 DETECTOR ON
THE CBM DETECTOR SYSTEM
The influence of the T0 detector on the CBM detector
system has been studied using Monte Carlo simulations.
The detector was placed at two locations in the simulations:
0.5 m and 2 m in front of the target. A point-like Au beamwith an energy of 4 A GeV and a rate of 107 ions/s was used.
The simulation assumed an Au target with a thickness of250 µm and 85% of the maximum magnetic field.
In a first study, the widening of the beam due to the diamond material was investigated. The results are shown inFig. 2. The beam profile is enlarged, but the halo particle
rate is not significantly increased. The ratio between thebeam spot maximum the beam spot center, at a distance
5 mm from the beam spot maximum, is eight orders of magnitude. This is in agreement with the guidelines of the CBM
collaboration.
The additional diamond material in front of the target
will also lead to an increased charged particle contaminationin the region where the Silicon Tracking System (STS) [5]is located. This is visualized in Fig. 2. However, initial
discussions with the CBM STS detector experts suggest that
this should not be problematic for its performance.

T0 MANIPULATOR PROTOTYPEThe T0 and halo detectors will be integrated into the CBM
beam line in front of the CBM target. The sensors will bemounted inside the vacuum, in standard CF 100 vacuum
chambers (see Fig. 3). The feed-through PCBs will be glued
into blind flanges.
The T0 detector will be operated for beam intensities of
107 particles/s. For higher beam intensities, the T0 detector
will need to be removed from the beam axis. We plan to usea step motor in combination with a flexible bellow to allow
the remote movement of the sensor from the beam axis. Aschematic drawing of a prototype, which is currently being
built, is shown in Fig. 3 (right).

Figure 2: Widening of the beam and charged particle contamination in the STS region for two different T0 positions.
Upper panel: The widening of the beam due to the diamond material of the T0 detector, which is located 50 cm(red curve) and 200 cm (blue curve) in front of the CBMtarget. Lower panel: The charged particle contamination inthe STS region for the two different T0 positions.

SENSOR MOUNT AND FEED-THROUGHPRINTED CIRCUIT BOARD
The T0 sensor will be bonded to a dedicated [6] printed circuit board (PCB) that serves as a sensor holder. A schematic
picture of such a PCB is shown in Fig. 4.
To compensate for radiation damage, which will result ina decrease of the signal amplitude, two analog amplification
stages are implemented close to the sensor. The sensor PCB
will be mounted inside the vacuum chambers. The feedthrough PCB (see green part in Fig. 4) will be glued into theflanges of the vacuum chamber.
The T0 detector is designed to operate at beam intensities
of up to 107 particles/s. Assuming a beam spot diameter of0.5 cm on the T0 sensor with a metalization of 16 stripes, arate of 1 MHz per readout channel is expected. The analog
signals are discriminated using the PADI ASIC [7] and aMOP018

02 Beam Position Monitors

67

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12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3

Content from this work may be used under the terms of the CC-BY-4.0 licence (© 2023). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI

12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3

IBIC2023, Saskatoon, CanadaJACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - M O P 0 1 8Figure 3: Schematic illustration of the manipulator system
for removing the T0 detector from the beam axis.
time-to-digital converter (TDC) is used, the Get4 ASIC [8].
Digital data is then sent to a single Common Readout Interface (CRI) board. A detailed description of the readout
system can be found in [2].

SUMMARY AND OUTLOOKA concept for the CBM BMON detector, consisting ofa T0 station and a halo station, has been developed. TheT0 station will be used to measure the time of arrival ofparticles with a precision of 50 ps. It will also be used forbeam monitoring purposes and as part of a fast beam abortsystem.
The system is currently planned to be based on polycrystalline chemical vapor deposition (pcCVD) diamondtechnology. However, we are also evaluating the recently developed Low Gain Avalanche Detector (LGAD) technology.
The impact of the T0 detector on the performance of theCBM detector system has been studied. It was found that theT0 detector does not negatively influence the performanceof the CBM detector system.
A manipulator system has been developed to remove theT0 detector from the beam axis. A demonstrator of themanipulator system is currently in production.
A prototype T0 detector based on pcCVD diamond material has been successfully tested at previous mCBM campaigns. For upcoming campaigns, we plan to further test theT0 detector and evaluate LGAD technology.

ACKNOWLEDGEMENTS
This project has received funding from the European
Union’s Horizon 2020 research and innovation programme
under grant agreement No. 871072. We would like to thankTU Darmstadt and GSI Detector Laboratory for the preparation of the diamond sensors.

Figure 4: Sensor mount and feed-through PCB. The sensor
will be glued into the recess and then bonded to the amplification stage input pads. Upper panel: One PCB is needed
for the T0 system. Lower panel: A mosaic arrangement offour PCBs is used for the halo system.

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ISSN: 2 6 7 3 - 5 3 5 0
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12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3