The P-ONE Demonstrator
The main target of the P-ONE demonstrator - as well as the first prototype line P-ONE-1 - is to test the system components and deployment strategy within the deep sea environment and to verify the expected detector performance. The P-ONE demonstrator is defined as the first cluster of the P-ONE detector and comprises ten instrumented mooring lines with total lengths of one kilometer, line spacings of 80 meters, and 20 optical modules with an inter-module spacing of 50 meters. P-ONE-1 will be deployed in 2025; the further lines will follow suit.
Detector Infrastructure
The P-ONE hybrid fiber-optic/copper cable is a single, deep sea-applicable cable that carries fiber communication and power to each of the instruments along its e length of 1 kilometer. These connections to individual modules are realized using a segmented cable. The required fiber and copper connections are spliced iteratively from the main cable at each instrument termination frame. This novel termination process allows using a single cable for the whole string while maintaining the possibility of exchanging full cable segments. The termination frames are made from titanium, and their splicing is s. On the surface end, the mooring line terminates with a buoyancy that maintains the upright position of the string. On the seafloor end, the cable terminates in the mJB, which hosts power controllers for each instrument, a synchronization unit, and a connection to the NEPTUNE network node. Here, a rugged steel tray is used to mount the mJB and to act as both a deployment tray and an anchor. Before deployment, the string is coiled on the tray, lowered to the sea floor, and unfurled once the anchor is in place. Data acquisition (DAQ) synchronization of the P-ONE detector is achieved using a newly developed system, BlackCat. This custom development employs the concept of the White Rabbit (WR) protocol but without using WR switches. Instead, a syntonous operation on layer-1 of Gigabit Ethernet (GbE) ensures sub-nanosecond synchronization between a central clock and all receiver endpoints.
Optical Modules
The two main instruments on the P-ONE mooring lines are regular optical modules (P-OMs) and calibration modules (P-CALs). Both are encapsulated in 17-inch borosilicate glass hemispheres, equipped with PMTs for light detection, and attached to the same instrument termination frame on the mooring line. However, while the P-OM carries eight PMTs per hemisphere, the P-CAL replaces four with different calibration systems. In total, 20 modules are located on each string, up to 3 being P-CALs and the remainder P-OMs. Optical coupling of the PMTs to the glass hemispheres is achieved using custom gel pads molded to the photosensitive area before assembly within the glass hemispheres. A custom, high-voltage sub-system provides each PMT with a self-regulated, programmable high-voltage supply. Analog output signals of the PMTs are fed to the P-OM mainboard, where they are digitized with an ADC at a rate of around 200 MHz. A field-programmable gate array (FPGA) provides the mainboard with a central control logic operating a Linux operating system and controlling DAQ, peripheral devices, synchronization, and communication. Each module has several temperature, pressure, humidity, acceleration, and magnetic field sensors for continuous system monitoring.
Calibration system
Real-time monitoring and calibration are of major importance for ocean-based detectors due to the dynamic deep-sea environments. The detector geometry, water optical properties, and bioluminescent light backgrounds vary with time due to changing ocean currents. Thus, the P-ONE calibration system comprises three main concepts: beamed and isotropic optical light pulsers, an acoustic positioning system, and integrated devices to measure sedimentation, acceleration, magnetic fields, and environmental parameters. In combination with the PMTs, these systems allow continuous monitoring of calibration parameters. Ten beamed, sub-nanosecond light flashers are integrated into every module, targeting measurements of time synchronization between instruments, light scattering, and spectral dispersion. P-CALs are further equipped with isotropic, high-power, nanosecond light pulsers, and a self-monitoring system based on the Precision Optical Calibration Module (POCAM) used for IceCube. This system determines the calibration of optical water properties, module efficiencies, and sedimentation. The acoustic positioning system is comprised of an acoustic transceiver system on the sea floor and acoustic receivers in each instrument. This allows precise monitoring of the string and module positions. At a later stage, acoustic positioning is planned to verify the introduction of a potential optical positioning system. Using sub-nanosecond light pulsers, a continuous, optical geometry calibration of P-ONE is envisioned. Lastly, in addition to environmental sensors included in all modules, P-CALs are further equipped with a camera system for monitoring sedimentation, biofouling, and bioluminescence.