About the Project
As part of the ongoing enhancement of the HiFi spectrometer at ISIS, Nuclear Instruments integrated the DAQ121—our high-speed, 1 Gsps, 12-bit digitizer—into the data acquisition chain alongside the legacy TDC system. This hybrid configuration enables advanced digital discrimination of PMT signals and real-time pile-up deconvolution, increasing temporal resolution and system flexibility for high-rate muon experiments.
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Date
April 2025
Nuclear Instruments
UKRI - Science and Technology Facilities Council
What is HiFi?
HiFi (High-Flux Instrument) is a high-resolution muon spectrometer installed at the ISIS Neutron and Muon Source. It was designed to address the need for high time-resolution measurements in muon spin spectroscopy (μSR) experiments, allowing researchers to study dynamic processes at the atomic scale with exceptional sensitivity. The spectrometer is optimized to detect subtle magnetic and electronic fluctuations in materials by capturing the time-resolved behavior of muon spin precession and relaxation.
HiFi leverages fast plastic scintillators coupled to photomultiplier tubes (PMTs), which register the arrival of positrons from muon decay. With a cylindrical arrangement of 96 detectors around the sample and a high-rate capable Time-to-Digital Converter (TDC) system, HiFi delivers precise event timing and high data throughput. The architecture is tailored to enable fine temporal discrimination of events, making it particularly valuable for studying fast spin dynamics, quantum materials, and systems under extreme conditions.
Our Contribution: Full DAQ System Integration for HiFi
Nuclear Instruments has played a central role in the DAQ upgrade of the HiFi spectrometer, delivering a complete solution from hardware to real-time data processing. Our contributions include:
- Design and production of the DAQ121 digitizer, a 1 Gsps, 12-bit ADC board optimized for fast spectroscopy
- Development of the digitizer firmware, enabling acquisition, triggering, timestamping, and waveform buffering
- Implementation of FPGA pipelines for real-time computation of muon lifetime and energy spectra, directly on the digitizer hardware
- Direct integration of the DAQ121 system with IBEX, allowing full remote control and monitoring within the ISIS control ecosystem
- Connection to Grafana dashboards, including custom metrics for acquisition status, digitizer temperature, and system diagnostics
- Kafka-based data streaming, linking the waveform acquisition flow to high-throughput pipelines for live processing and long-term storage
DAQ121 Integration into HiFi: Advancing Digital Signal Processing
Nuclear Instruments has successfully integrated the DAQ121 digitizer — a 1 Gsps, 12-bit device — into the HiFi acquisition system. This integration complements the existing 96-channel TDC (one for each PMT) and aims to demonstrate the benefits of direct analog signal sampling from the PMTs, enabling digital event discrimination, especially in scenarios characterized by severe pile-up.
The system is engineered to acquire PMT signals following a trigger generated by a Cherenkov scintillator placed at the entrance of the muon beamline. Upon receiving this trigger, the digitizer captures the analog waveform, which is then transmitted via a pipeline architecture to a processing server. There, deconvolution-based algorithms are applied to resolve spatial pile-up, a key challenge in high-flux experiments.
On the sampled waveform, a dual-threshold mechanism is implemented — both in time and energy — achieving an effective time resolution of 1 ns peak-to-peak. Looking forward, the system design accommodates future digital CFD (Constant Fraction Discriminator) algorithms, paving the way for enhanced spatial resolution. Preliminary results already demonstrate sub-100 ps resolution within specific channel groups.
Photo: DAQ121 digitizers in the HiFi acquisition cabinet
Photo: DAQ121 digitizers in the HiFi acquisition cabinet
Full Integration into the ISIS Control Ecosystem
The upgraded system is fully integrated into IBEX, the SCADA (Supervisory Control and Data Acquisition) framework used at ISIS. Real-time monitoring of system parameters is implemented through Grafana, providing clear visibility and operational control.
Screenshot: IBEX interface displaying digitizer parameters
Each DAQ121 digitizer autonomously sends data to a dedicated InnoDB database. This architecture enables the storage and retrieval of essential system diagnostics, which are then visualized via custom Grafana dashboards — in a structure similar to that used for the MuSR and SuperMUSR instruments.
Screenshot: Grafana dashboard for HiFi digitizer performance and DAQ temperature monitoring
Screenshot: Grafana dashboard for HiFi digitizer performance and DAQ temperature monitoring
Screenshot: Grafana dashboard for HiFi digitizer acquisition status and DAQ monitoring
Screenshot: Grafana dashboard for HiFi digitizer acquisition status and DAQ monitoring
Screenshot: Grafana dashboard status packet timing and frame distribution system monitoring
Screenshot: Grafana dashboard status packet timing and frame distribution system monitoring
HiFi Data Acquisition Architecture
The diagram represents the architecture of the upgraded HiFi data acquisition system, highlighting the parallel processing paths and real-time integration of control and analysis components. The ADC feeds both the Processing Firmware and the Acquisition Firmware, enabling simultaneous signal analysis and acquisition. The Acquisition Firmware interfaces with the DMA engine, and also receives timing signals from the Trigger T0 and TDC subsystems to synchronize event detection. All acquired data is funneled into the Embedded DAQ Software, which not only communicates with the processing chain but also branches into three output streams: Slow Control & Monitoring, Waveform Acquisition, and Real-time Lifetime & Energy Histogram. The Slow Control and Real-time Histogram streams are routed to the IBEX Server, enabling full integration with the IBEX Client interface used at ISIS. Meanwhile, waveform data is pushed to a Kafka Producer, which delivers it into a Kafka Pipeline. This pipeline feeds both persistent Storage and a Real-time Data Processing module, whose output is directed to Mantid, the analysis software used for scientific interpretation. This architecture ensures high-speed data flow, robust control, and the ability to apply advanced digital signal processing and live diagnostics in complex experimental environments.
Processing diagram of the HiFi digitizer system from acquisition to data storage and analisys.
Processing diagram of the HiFi digitizer system from acquisition to data storage and analisys.
