Low gain avalanche diodes for timing applications

This work aims to develop a non-destructive beam time structure monitoring system for the superconducting Darmstadt linear accelerator (S-DALINAC). The S-DALINAC is a 3 GHz superconducting electron accelerator capable of operations in the energy recovery (ERL) mode. The ERL operation mode allows the recovery of the beam energy and uses it for an acceleration of consecutive bunches. It is reached by recirculating the beam to the main LINAC with a 180° phase shift with respect to the phase of the electric field in the accelerator cavities. During the operation in the ERL mode, one beamline recirculates two beams simultaneously, leading to the 6 GHz repetition rate inside this beamline. To monitor both beams, a detector system capable of resolving this time structure of 6 GHz has to be built. For this purpose, a test setup based on the Low Gain Avalanche Diodes (LGADs), silicon sensors designed for high-precision simultaneous position and time measurement, was developed. Several groups have demonstrated a time resolution below 50 ps for LGADs, which indicates that this technology is a suitable candidate for the beam time structure monitoring at the S-DALINAC. The read-out system was based on leading-edge discriminators and Field-Programmable Gate Array (FPGA) based Time-to-Digital converters (TDCs) developed at GSI in Darmstadt, Germany. These allow for the estimation of arrival time and signal width via the time-over-threshold method. To demonstrate the feasibility of an LGAD-based beam time structure monitoring system, a simplified setup based on a single 1 cm×0.5 cm LGAD sensor with a limited number of active channels was prepared and tested at the experimental hall at the S-DALINAC. Due to the placement of the setup, the delivered beam had a 3 GHz time structure. During this proof-of-principle demonstration, the S-DALINAC 3 GHz beam time structure was successfully resolved for the first time. An upgraded setup, which employed two 1 cm×1 cm LGAD sensors, was prepared to investigate the feasibility and performance of an LGAD-based beam time structure monitoring system. In contrast to the first proof-of-principle experiment, the entire system was read out using an upgraded version of the read-out system. Also, with this upgraded setup, the 3 GHz time structure was successfully resolved, and an intrinsic time resolution of 79 ps was demonstrated. Since the setup installation for the proof-of-concept study had to be done outside of the accelerator hall, only the beam with the 3 GHz time structure could be measured. A design concept study using Geant4 simulations was performed as a next step to investigate the feasibility of an LGAD-based beam time structure monitoring system for the ERL mode. To evaluate the LGAD’s performance in such conditions, a simulation with the simplified geometry of the potential measurement station was prepared. This simulation demonstrated the feasibility of an LGAD-based system for monitoring the 6 GHz beam time structure. Additionally, the best detector position inside the accelerator hall could be identified. In the upcoming runs at the S-DALINAC, it will be possible to verify the results of simulations and the concept. Lastly, the feasibility of the machine learning (ML) approach for the LGADs data analysis was demonstrated. It was shown that the ML approach reduces the amount of data required for the LGAD correction without distorting the time resolution. Additionally, this approach can be used to implement an online LGAD correction procedure

Beam-diagnostic and T0 System for the mCBM and CBM Experiments at GSI and FAIR

The Compressed Baryonic Matter (CBM) experiment at the Facility for Antiproton and Ion Research (FAIR) in Darmstadt requires a highly accurate beam monitoring and time-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 achieve these 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

First experimental time-of-flight-based proton radiography using low gain avalanche diodes

Ion computed tomography (iCT) is an imaging modality for the direct determination of the relative stopping power (RSP) distribution within a patient's body. Usually, this is done by estimating the path and energy loss of ions traversing the scanned volume via a tracking system and a separate residual energy detector. This study, on the other hand, introduces the first experimental study of a novel iCT approach based on time-of-flight (TOF) measurements, the so-called Sandwich TOF-iCT concept, which in contrast to any other iCT system, does not require a residual energy detector for the RSP determination. A small TOF-iCT demonstrator was built based on low gain avalanche diodes (LGAD), which are 4D-tracking detectors that allow to simultaneously measure the particle position and time-of-arrival with a precision better than 100um and 100ps, respectively. Using this demonstrator, the material and energy-dependent TOF was measured for several homogeneous PMMA slabs in order to calibrate the acquired TOF against the corresponding water equivalent thickness (WET). With this calibration, two proton radiographs (pRad) of a small aluminium stair phantom were recorded at MedAustron using 83 and 100.4MeV protons. Due to the simplified WET calibration models used in this very first experimental study of this novel approach, the difference between the measured and theoretical WET ranged between 37.09 and 51.12%. Nevertheless, the first TOF-based pRad was successfully recorded showing that LGADs are suitable detector candidates for TOF-iCT. While the system parameters and WET estimation algorithms require further optimization, this work was an important first step to realize Sandwich TOF-iCT. Due to its compact and cost-efficient design, Sandwich TOF-iCT has the potential to make iCT more feasible and attractive for clinical application, which, eventually, could enhance the treatment planning quality

First experimental time-of-flight-based proton radiography using low gain avalanche diodes

Ion computed tomography (iCT) is an imaging modality for the direct determination of the relative stopping power (RSP) distribution within a patient's body. Usually, this is done by estimating the path and energy loss of ions traversing the scanned volume via a tracking system and a separate residual energy detector. This study, on the other hand, introduces the first experimental study of a novel iCT approach based on time-of-flight (TOF) measurements, the so-called Sandwich TOF-iCT concept, which in contrast to any other iCT system, does not require a residual energy detector for the RSP determination. A small TOF-iCT demonstrator was built based on low gain avalanche diodes (LGAD), which are 4D-tracking detectors that allow to simultaneously measure the particle position and time-of-arrival with a precision better than 100um and 100ps, respectively. Using this demonstrator, the material and energy-dependent TOF was measured for several homogeneous PMMA slabs in order to calibrate the acquired TOF against the corresponding water equivalent thickness (WET). With this calibration, two proton radiographs (pRad) of a small aluminium stair phantom were recorded at MedAustron using 83 and 100.4MeV protons. Due to the simplified WET calibration models used in this very first experimental study of this novel approach, the difference between the measured and theoretical WET ranged between 37.09 and 51.12%. Nevertheless, the first TOF-based pRad was successfully recorded showing that LGADs are suitable detector candidates for TOF-iCT. While the system parameters and WET estimation algorithms require further optimization, this work was an important first step to realize Sandwich TOF-iCT. Due to its compact and cost-efficient design, Sandwich TOF-iCT has the potential to make iCT more feasible and attractive for clinical application, which, eventually, could enhance the treatment planning quality

First experimental time-of-flight-based proton radiography using low gain avalanche diodes

Objective. Ion computed tomography (iCT) is an imaging modality for the direct determination of the relative stopping power (RSP) distribution within a patient's body. Usually, this is done by estimating the path and energy loss of ions traversing the scanned volume utilising a tracking system and a separate residual energy detector. This study, on the other hand, introduces the first experimental study of a novel iCT approach based on time-of-flight (TOF) measurements, the so-called Sandwich TOF-iCT concept, which in contrast to any other iCT systems, does not require a residual energy detector for the RSP determination. Approach. A small Sandwich TOF-iCT demonstrator was built based on low gain avalanche diodes (LGADs), which are 4D-tracking detectors that allow to simultaneously measure the particle position and time-of-arrival with a precision better than 100 μm and 100 ps, respectively. Using this demonstrator, the material and energy-dependent TOF was measured for several homogeneous PMMA slabs in order to calibrate the acquired TOF against the corresponding water equivalent thickness (WET). With this calibration, two proton radiographs (pRads) of a small aluminium stair phantom were recorded at MedAustron using 83 MeV and 100.4 MeV protons. Main results. Due to the simplified WET calibration models used in this very first experimental study of this novel approach, the difference between the measured and theoretical WET ranged between 37.09% and 51.12%. Nevertheless, the first TOF-based pRad was successfully recorded showing that LGADs are suitable detector candidates for Sandwich TOF-iCT. Significance. While the system parameters and WET estimation algorithms require further optimization, this work was an important first step to realize Sandwich TOF-iCT. Due to its compact and cost-efficient design, Sandwich TOF-iCT has the potential to make iCT more feasible and attractive for clinical application, which, eventually, could enhance the treatment planning quality

New results on light nuclei, hyperons and hypernuclei from HADES (HADES collaboration)

International audienceIn March 2019 the HADES experiment recorded 14 billion Ag+Ag collisions at √sNN = 2.55 GeV as a part of the FAIR phase-0 physics program. In this contribution, we present and investigate our capabilities to reconstruct and analyze weakly decaying strange hadrons and hypernuclei emerging from these collisions. The focus is put on measuring the mean lifetimes of these particles