In the Karlsruhe Tritium Neutrino Experiment, an international group of 200 researchers has joined forces to measure the mass of neutrinos. Neutrinos are the lightest, most common, but also the most puzzling particles in our universe. They are electrically neutral and interact with their environment only through gravity and the so-called weak nuclear force. This makes it difficult to measure their properties and the list of technical challenges to be solved is long.
Description of the experiment
In the KATRIN experiment, the mass of the electron antineutrino is to be limited by highly precise energy determination of tritium decay electrons (β radiation). The most striking component of the experiment is a very large electrostatic retardation spectrometer formed by a stainless steel vessel of 10 m diameter. By means of a high voltage source (approx. -18.6 kV), an electric counter field is formed in it, which causes a large part of the electrons to bounce back. The few b-electrons passing through the spectrometer are registered by a silicon detector.
Such a large-scale experiment also requires very highly specialized components in the field of electronics, which can only be developed in close interdisciplinary collaboration in the experiment collaboration.
The IPE is currently collaborating on the KATRIN experiment with the following contributions
Management of electronics-related KATRIN tasks
Slow control (experiment control and monitoring) and data management
Detectors and electronics
Highly specialized measurement technology
Fast data acquisition (detector signals)
High voltage stabilization
Advice/support in electronics-related questions
Slow control and data management
The main components such as the spectrometers and the tritium source are highly complex systems. A multitude of technical challenges such as ultra-high vacuum, high magnetic fields, high voltage in the range of a few kilovolts, cryogenic temperatures in the superconducting magnets or bakeout temperatures of 300°C have to be taken into account, sometimes simultaneously. In addition to low-noise detectors for the detection of charged elementary particles, the KATRIN experiment also places high demands on the automation technology, the so-called "slow control". To ensure safe operation on the one hand and to provide the necessary flexibility of a physical experiment on the other hand, the Slow Control is divided into the control of the basic machine and a physical monitoring and control system. The former is realized by robust process control technology. The control of the particularly safety-critical tritium source in the radiation protection monitoring area was developed at the institutes ITEP and IK, where corresponding experience was already available. The monitoring system will be set up under the leadership of the IPE. In order to allow a flexible integration of different systems, a system has been developed which allows the central acquisition and control of the subsystems. The tasks of the physical monitoring and control system include, for example, 3D temperature monitoring, the distributed high-voltage system, magnetic field monitoring and correction, and the entire detector area.
The ADEI data management system was created to make the relevant data from all system parts centrally available. This system accesses the original data of the individual systems and checks consistency and data quality and then performs standard analyses. The entire data stock is made available to the entire experiment collaboration on the Internet via the KATRIN Experiment Portal. A fast interactive navigation is enabled by an intelligent caching strategy.
Visualization of the temperature distribution of the main spectrometer tank
DAQ and databases
Key technologies that IPE has developed in KATRIN are
Framework for flexible "slow control" systems
For automation tasks PC-based measurement and control systems combined with flexible programming in LabView are used. Standard interfaces such as OPC, web services and SQL databases allow easy integration into data acquisition and data management systems. The system was used to implement various monitoring instruments.
Fast data acquisition for pixelated detectors
The multi-channel IPE-DAQ electronics are used to read out the KATRIN main detector. The flexible and programmable FPGA-based system is integrated into the graphical object-oriented real-time control and acquisition system ORCA.
Data management for international scientific collaborations
The Advanced Data Extraction Infrastructure ADEI was developed to provide easy, referenceable, worldwide access to the complete data of an experiment. Through its programming interface and web data portal, ADEI combines unified access to international collaborations. It has a modular structure to integrate data from very different sources. Currently, several gigabytes of data are recorded daily, which add up to terabytes of slow control data managed by ADEI.
Computing and data infrastructure
Complex experimental setups require a reliable and powerful computing infrastructure to ensure data acquisition, storage and fast access to the data. The KATRIN infrastructure uses a redundant LAN ring, a hierarchical storage system. Virtualization and cloud services are used to optimize flexibility and minimize maintenance efforts.
Further information is available at https://ufo.kit.edu/dis/index.php/ufo/katrin.
Low-latency Big Data Visualisation - Tan Jerome, Nicholas PhD thesis, Faculty of Electrical Engineering and Information Technology, Karlsruhe Institute of Technology, 2019.
Focal-plane detector system for the KATRIN experiment - Amsbaugh, J.F. et al. in Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment Volume 778, 1 April 2015, Pages 40-60
Characterization of an FPGA-based DAQ system in the KATRIN experiment - Phillips, D.G et al. in IEEE Nuclear Science Symposium Conference Record 2010, Article number 5874002, Pages 1399-1403
Advanced data extraction infrastructure: Web based system for management of time series data - Chilingaryan, S., et al. in Journal of Physics: Conference Series. Vol. 219. No. 4. IOP Publishing, 2010.
The IPE developed the electronics for the then "pre-spectrometer experiment" (64 pixels or channels) and the electronics for the main spectrometer detector (148 pixels or channels). Both are multi-element silicon PIN detectors for low-energy β electrons, which are produced during the radioactive decay of tritium. The special requirements are the high integration density, the low noise, the operation in a high magnetic field, the operation in a vacuum and the galvanic isolation, which is necessary due to a post-acceleration device. Safety and monitoring components for operation are also required.
The detector electronics were also developed for numerous auxiliary experiments:
- In the so-called TRAP experiment, tritium was to be detected under difficult mechanical conditions with a relatively large area Si-PIN detector (300mm²).
- The so-called Forward Beam Monitor is operated in the full electron flow of the tritium source and in a very high magnetic field and must be mechanically pivotable.
- In the so-called monitor spectrometer, the equipment of the Mainz neutrino mass experiment is still used, but the detector electronics had to be revised.
- A 14-element silicon detector for operation in ultra-high vacuum and in a very high magnetic field was required for the commissioning of the KATRIN differential pumping section 2F.
Sectional drawing of the KATRIN 148-pixel main detector
Test stand for the electronics and data acquisition of the KATRIN main detector
Ceramic assembly with main detector preamplifiers
The 64-pixel pre-spectrometer detector
Preamplifier stage for the TRAP detector, built in hybrid technology
Preamplifier stage for the "Forward Beam Monitor" on ceramic substrate (in cooperation with the Institute of Nuclear Physics)
electronic boxes for the KATRIN veto detector. In the boxes, weak light pulses consisting of only a few photons are converted into electrical pulses.
Detector data acquisition system (data acquisition, DAQ)
to the technology DAQ electronics for multi-channel detectors
High voltage supply and high voltage safety
The retardation voltage of the main spectrometer, which can be up to 35 kV for calibration measurements, is one of the most important accuracy relevant key parameters of the KATRIN experiment: Accuracy in the ppm range up to the high frequency range is required. In addition, there are complex EMC requirements due to the unshielded, spatially extensive arrangement (main spectrometer tank). The ultra-precision measurement of the high voltage developed by the University of Münsteris supplemented by a specially developed control technology which ensures the most accurate maintenance of the high voltage even up to the MHz range.
Furthermore, due to the large extension of the experiment, special attention has to be paid to the electrical reference potential used by different parts of the facility. Despite the danger of interference coupling, it must be ensured that the reference potential is accurate at all points in the mV range.
Furthermore, because of the high voltage carrying parts, safety precautions must of course also be taken, such as shut-off measures and emergency shut-off devices.
Diagram of the high-precision retardation voltage readjustment
For monitoring the magnetic field at the main spectrometer, which is generated by the Low Field Coil System (LFCS, air coils with 12 m diameter!), the IPE developed a low-cost multi-point 3D magnetometer. A considerable cost saving compared to commercial magnetometers could be achieved by optimal adaptation to the KATRIN requirements.
KATRIN Low Field Magnetometer IPE-316/5
Magnetic field measuring robots developed by the University of Applied Sciences Fulda are supported and further developed by the IPE
Magnet safety systems for superconducting magnets
In the KATRIN experiment, the axial guidance of the beta electrons from the tritium decay is achieved by strong axial magnetic fields generated by superconducting coils.
In the plant sections "WGTS" (Windowless Gaseous Tritium Source) and "CPS" (Cryo Pumping Section), these coils are operated in the so-called "Driven Mode", in which the power supply units are permanently connected and control the coil current.
Special monitoring devices are required to protect the magnetic coil from damage in the event of a quench (sudden loss of superconductivity during operation). A quench detection system (QDS) developed at the IPE is used in combination with a PLC control system and other components that have been specially developed for KATRIN.
IPE quench detection system "UniQD
High-current power supply unit (left) and DC switchboard with high-current circuit breakers (top right) and high-power load resistor (bottom right)
The IPE coordinates the construction and maintenance of the KATRIN IT infrastructure. Due to the different safety requirements (from the networking of safety-relevant process control units to simple PC office and internet applications), a structure with several parallel fibre optic ring lines was chosen.
- Advising the KATRIN collaboration on electrotechnical issues such as EMV/earthing/high voltage
- Co-supervision of interns, diploma and doctoral students in electrical/information technology topics