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Self-triggering readout system for the neutron lifetime experiment PENeLOPE
Nuclear Instruments and Methods in Physics Research A 824 (2016) 290–291
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Self-triggering readout system for the neutron lifetime experiment PENeLOPE D. Gaisbauer a,n, I. Konorov a, D. Steffen b, S. Paul a a b
Technische Universität München, Garching, Germany CERN, Geneva, Switzerland
art ic l e i nf o
a b s t r a c t
Available online 24 October 2015
The aim of PENeLOPE (Precision Experiment on Neutron Lifetime Operating with Proton Extraction) at the Forschungsreaktor München II is a high-precision measurement of the neutron lifetime and thereby an improvement of the parameter's precision by one order of magnitude. In order to achieve a higher accuracy, modern experiments naturally require state-of-the-art readout electronics, as well as highperformance data acquisition systems. This paper presents the self-triggering readout system designed for PENeLOPE which features a continuous pedestal tracking, configurable signal detection logic, floating ground up to 30 kV, cryogenic environment and the novel Switched Enabling Protocol (SEP). The SEP is a time-division multiplexing transport level protocol developed for a star network topology. & 2015 Elsevier B.V. All rights reserved.
Keywords: DAQ Systems Front End Electronics
1. Introduction The PENeLOPE experiment is a neutron lifetime experiment aiming at a precision measurement better than 0.1 s [1]. It is developed at the Technische Universität München. Ultra cold neutrons (UCNs) will be trapped in a magnetic field created by 28 specially designed superconducting coils. As gravitational forces will keep the neutrons in the trap a decay particle detector is placed on top of the coils. The protons from neutron decays are accelerated by a high electric field towards the detector in order to overcome the magnetic mirror effect. Fig. 1 shows a CAD model of the latest design of the PENeLOPE experiment. Due to this design, the data acquisition and slow control system has to fulfil several requirements including high post-acceleration voltage of 30 kV, magnetic fields of 0.6 T, temperatures of 77 K, high vacuum of 10 8 mbar, single proton counting, and active area of 0.23 m2. Fig. 2 shows the general set up of the readout electronics of the proton detector from PENeLOPE.
2. Analog electronics Protons accelerated by the high voltage are detected with Hamamatsu S8664 avalanche photo diodes (APDs) of 10 mm by 10 mm size. In order to cover the large area, 1000 APDs will be used in the final stage of PENeLOPE. The electron avalanche n
Corresponding author. E-mail address: [email protected] (D. Gaisbauer).
http://dx.doi.org/10.1016/j.nima.2015.10.049 0168-9002/& 2015 Elsevier B.V. All rights reserved.
created by a proton hitting the APD is amplified in a charge sensitive pre-amplifier and then reshaped in a CR-RC circuit. The time constants of the shaper are about 1 μs. The signal is digitized by a 12-bit ADC (AD7450) with 1 Mbps and subsequently processed in the FPGA. Fig. 3 shows a waveform of a digitized proton signal.
3. Signal detection unit (SDU) The PENeLOPE frontend electronics consists of 10 SDUs which utilize Xilinx Spartan 6 LX150T FPGA. One SDU controls 4 ADC cards with 25 channels each. The SDU continuously determines pedestal value and measures noise of each channel. The signal detection logic calculates the threshold by multiplying the noise value by a common for all channels programmable parameter [2]. Furthermore the detection logic runs at 120 MHz and processes all 100 channels which are sampled with 1 MHz. A signal is detected when a programmable number of consecutive samples exceed the threshold. The data of the detected signals is combined to an event by tagging them with the channel ID and the absolute time. These events are then transferred via a serial optical link to the NAC for further processing.
4. Network access controller (NAC) A Xilinx Virtex 6 LX130T FPGA is the heart of the NAC. The module collects the data from all SDUs and sends it to the DAQ computer via Ethernet using the UDP protocol. The measured data throughput for this connection is about 50 MB/s. Additionally all
D. Gaisbauer et al. / Nuclear Instruments and Methods in Physics Research A 824 (2016) 290–291
291
⁄
GB s
0.120
0.115
0.110 0
Vacuum Tank SDUs
1000
2000
3000
4000
Buffer size in kbit
2.4 m
Analog Electronics and APDs lHe Cooled Coils Neutron Storage Volume Neutron Guide
Fig. 4. Maximum bandwidth versus buffer size for fixed readout rate of 1 Gbps.
Table 1 Link utilization efficiency for 16 slaves and different transmission times. Transmission time (μs)
Efficiency (%)
25,000 10,000 1000 500 100
99.93 99.84 98.42 96.90 86.20
Fig. 1. CAD model of the PENeLOPE experiment.
25 APDs
Inside of Outside of Cryostat Cryostat
PreAmp, Shaper, ADC 4x PreAmp, Shaper, ADC
SDU01 Spartan 6
...
25 APDs
...
10x 25 APDs
PreAmp, Shaper, ADC 4x PreAmp, Shaper, ADC
Op cal Spl er
SDU10 Spartan 6
...
25 APDs
30 kV high Ground Voltage Poten al
Slow Control PC
NAC Virtex 6
IPBus UDP DAQ PC
Slow Control Spartan 6
BIAS
Fig. 2. Set up of readout electronics for the proton detector of PENeLOPE.
and up to 256 slaves. SEP is a further development of the SODA time distribution system of the PANDA experiment [3]. There are one master and multiple slave modules connected with a single fiber using a passive optical splitter. Time-division parameters are programmable and are a trade-off between buffer sizes and a bandwidth efficiency utilization. Fig. 4 shows the maximum bandwidth with equal load for all SDUs and 1 Gbps link speed. SEP supports data transmission, slow control interfaces (IPbus) and distribution of synchronous messages with deterministic latency. In the case of PENeLOPE each of the 16 slaves gets a 1 ms time window to transmit detector and slow control data. The access window is sequentially moved from one slave to another in a Round-Robin manner. For PENeLOPE the overall bandwidth utilization efficiency is about 98%. Table 1 shows the efficiency for different transmission times with 16 slaves.
500
ADC channel
400
Acknowledgments
300
The authors would like to thank Stefan Huber, Dmytro Levit, Wolfgang Schreyer and Christian Tietze for generous support during the testing activities. This work is supported by the Maier-LeibnitzLaboratorium (Garching), the Deutsche Forschungsgemeinschaft (DFG) and the Excellence Cluster “Origin and Structure of the Universe”.
200 100 0 −100 0
20
40
60
80
100
time (µ s)
References
Fig. 3. Signal shape after ADC.
environmental, control and monitoring data is multiplexed and send out via the IPbus protocol [4] to the slow control computer.
5. Switched enabling protocol (SEP) The SEP is a time-division multiplexing transport level protocol developed for a star-like optical network topology with one master
[1] R. Picker, PENeLOPE and AbEx on the way towards a new precise neutron lifetime measurement (PhD), Technische Universität München, 2008. [2] D. Steffen, Self-triggering readout system with advanced online data processing for the proton detection of the neutron lifetime experiment PENeLOPE (MSc), Technische Universität München, 2014. [3] I. Konorov, et al., SODA: time distribution system for the PANDA experiment, in: Nuclear Science Symposium Conference Record (NSS/MIC), 2009, pp. 1863– 1865. [4] IPbus project website: 〈https://svnweb.cern.ch/trac/cactus〉, 2015.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Self-triggering readout system for the neutron lifetime experiment PENeLOPE D. Gaisbauer a,n, I. Konorov a, D. Steffen b, S. Paul a a b
Technische Universität München, Garching, Germany CERN, Geneva, Switzerland
art ic l e i nf o
a b s t r a c t
Available online 24 October 2015
The aim of PENeLOPE (Precision Experiment on Neutron Lifetime Operating with Proton Extraction) at the Forschungsreaktor München II is a high-precision measurement of the neutron lifetime and thereby an improvement of the parameter's precision by one order of magnitude. In order to achieve a higher accuracy, modern experiments naturally require state-of-the-art readout electronics, as well as highperformance data acquisition systems. This paper presents the self-triggering readout system designed for PENeLOPE which features a continuous pedestal tracking, configurable signal detection logic, floating ground up to 30 kV, cryogenic environment and the novel Switched Enabling Protocol (SEP). The SEP is a time-division multiplexing transport level protocol developed for a star network topology. & 2015 Elsevier B.V. All rights reserved.
Keywords: DAQ Systems Front End Electronics
1. Introduction The PENeLOPE experiment is a neutron lifetime experiment aiming at a precision measurement better than 0.1 s [1]. It is developed at the Technische Universität München. Ultra cold neutrons (UCNs) will be trapped in a magnetic field created by 28 specially designed superconducting coils. As gravitational forces will keep the neutrons in the trap a decay particle detector is placed on top of the coils. The protons from neutron decays are accelerated by a high electric field towards the detector in order to overcome the magnetic mirror effect. Fig. 1 shows a CAD model of the latest design of the PENeLOPE experiment. Due to this design, the data acquisition and slow control system has to fulfil several requirements including high post-acceleration voltage of 30 kV, magnetic fields of 0.6 T, temperatures of 77 K, high vacuum of 10 8 mbar, single proton counting, and active area of 0.23 m2. Fig. 2 shows the general set up of the readout electronics of the proton detector from PENeLOPE.
2. Analog electronics Protons accelerated by the high voltage are detected with Hamamatsu S8664 avalanche photo diodes (APDs) of 10 mm by 10 mm size. In order to cover the large area, 1000 APDs will be used in the final stage of PENeLOPE. The electron avalanche n
Corresponding author. E-mail address: [email protected] (D. Gaisbauer).
http://dx.doi.org/10.1016/j.nima.2015.10.049 0168-9002/& 2015 Elsevier B.V. All rights reserved.
created by a proton hitting the APD is amplified in a charge sensitive pre-amplifier and then reshaped in a CR-RC circuit. The time constants of the shaper are about 1 μs. The signal is digitized by a 12-bit ADC (AD7450) with 1 Mbps and subsequently processed in the FPGA. Fig. 3 shows a waveform of a digitized proton signal.
3. Signal detection unit (SDU) The PENeLOPE frontend electronics consists of 10 SDUs which utilize Xilinx Spartan 6 LX150T FPGA. One SDU controls 4 ADC cards with 25 channels each. The SDU continuously determines pedestal value and measures noise of each channel. The signal detection logic calculates the threshold by multiplying the noise value by a common for all channels programmable parameter [2]. Furthermore the detection logic runs at 120 MHz and processes all 100 channels which are sampled with 1 MHz. A signal is detected when a programmable number of consecutive samples exceed the threshold. The data of the detected signals is combined to an event by tagging them with the channel ID and the absolute time. These events are then transferred via a serial optical link to the NAC for further processing.
4. Network access controller (NAC) A Xilinx Virtex 6 LX130T FPGA is the heart of the NAC. The module collects the data from all SDUs and sends it to the DAQ computer via Ethernet using the UDP protocol. The measured data throughput for this connection is about 50 MB/s. Additionally all
D. Gaisbauer et al. / Nuclear Instruments and Methods in Physics Research A 824 (2016) 290–291
291
⁄
GB s
0.120
0.115
0.110 0
Vacuum Tank SDUs
1000
2000
3000
4000
Buffer size in kbit
2.4 m
Analog Electronics and APDs lHe Cooled Coils Neutron Storage Volume Neutron Guide
Fig. 4. Maximum bandwidth versus buffer size for fixed readout rate of 1 Gbps.
Table 1 Link utilization efficiency for 16 slaves and different transmission times. Transmission time (μs)
Efficiency (%)
25,000 10,000 1000 500 100
99.93 99.84 98.42 96.90 86.20
Fig. 1. CAD model of the PENeLOPE experiment.
25 APDs
Inside of Outside of Cryostat Cryostat
PreAmp, Shaper, ADC 4x PreAmp, Shaper, ADC
SDU01 Spartan 6
...
25 APDs
...
10x 25 APDs
PreAmp, Shaper, ADC 4x PreAmp, Shaper, ADC
Op cal Spl er
SDU10 Spartan 6
...
25 APDs
30 kV high Ground Voltage Poten al
Slow Control PC
NAC Virtex 6
IPBus UDP DAQ PC
Slow Control Spartan 6
BIAS
Fig. 2. Set up of readout electronics for the proton detector of PENeLOPE.
and up to 256 slaves. SEP is a further development of the SODA time distribution system of the PANDA experiment [3]. There are one master and multiple slave modules connected with a single fiber using a passive optical splitter. Time-division parameters are programmable and are a trade-off between buffer sizes and a bandwidth efficiency utilization. Fig. 4 shows the maximum bandwidth with equal load for all SDUs and 1 Gbps link speed. SEP supports data transmission, slow control interfaces (IPbus) and distribution of synchronous messages with deterministic latency. In the case of PENeLOPE each of the 16 slaves gets a 1 ms time window to transmit detector and slow control data. The access window is sequentially moved from one slave to another in a Round-Robin manner. For PENeLOPE the overall bandwidth utilization efficiency is about 98%. Table 1 shows the efficiency for different transmission times with 16 slaves.
500
ADC channel
400
Acknowledgments
300
The authors would like to thank Stefan Huber, Dmytro Levit, Wolfgang Schreyer and Christian Tietze for generous support during the testing activities. This work is supported by the Maier-LeibnitzLaboratorium (Garching), the Deutsche Forschungsgemeinschaft (DFG) and the Excellence Cluster “Origin and Structure of the Universe”.
200 100 0 −100 0
20
40
60
80
100
time (µ s)
References
Fig. 3. Signal shape after ADC.
environmental, control and monitoring data is multiplexed and send out via the IPbus protocol [4] to the slow control computer.
5. Switched enabling protocol (SEP) The SEP is a time-division multiplexing transport level protocol developed for a star-like optical network topology with one master
[1] R. Picker, PENeLOPE and AbEx on the way towards a new precise neutron lifetime measurement (PhD), Technische Universität München, 2008. [2] D. Steffen, Self-triggering readout system with advanced online data processing for the proton detection of the neutron lifetime experiment PENeLOPE (MSc), Technische Universität München, 2014. [3] I. Konorov, et al., SODA: time distribution system for the PANDA experiment, in: Nuclear Science Symposium Conference Record (NSS/MIC), 2009, pp. 1863– 1865. [4] IPbus project website: 〈https://svnweb.cern.ch/trac/cactus〉, 2015.