LOFAR2.0 Newsletter December 2020
The year 2020 is already nearing its end. It has been a very different year from what we were used to. Fortunately, we have found new ways to keep in touch and to continue our activities. It is great to see the technical design progressing! We can be very proud of what we achieved this year, and in particular on how it was achieved. First of all because many of the highlights presented in the Newsletter have been implemented from our home offices. Secondly, because new ways of working were introduced, and the ASTRON organisation has changed significantly in the meantime. The new ASTRON structure and the intensified interaction between LOFAR2.0 and the Astronomy and Operations department is crucial for a successful LOFAR2.0!
I conclude by wishing you Happy Holidays. Thank you for your efforts, flexibility and the excellent collaboration. Enjoy some well-deserved time off with your family and friends, and stay safe!
The development in LOFAR2.0 goes full steam ahead and the first prototypes are already under test. Early integration of the tested products is key to reduce integration risks early in the program. A systems engineering master schedule has been created wherein the integration steps for the telescope are defined. It connects program stages with planned functionality upgrades, and it shows that various sub-systems need to be updated over time. In this way, the system evolves steadily from LOFAR1 to LOFAR2.0. An overview of the Systems Engineering Master schedule of LOFAR2.0 is depicted in Figure 1.
The telescope is upgraded in five main phases, as is shown in the top row of Figure 1. Currently, we are aligning the various tasks with the project teams. Also, we are working on a more detailed plan which also shows the available functionality over time
First RCU2-H prototype board tested
Together with INAF, the first RCU2-H (high-band) prototype board has been prepared for testing and characterization. These new receivers have a larger dynamic range than the existing ones, enabling LOFAR2.0 to cope with higher levels of RFI without losing sensitivity. As in RCU2-L, the board can handle three channels independently, but the larger footprint of the analog part required the designers to spread the components over two sides of the board, which proved quite a challenge to prevent coupling.
In the top picture below you can see the board itself on the left, connected to the earlier developed ASTRON digital board on the right, together with the old RCU board as is used in the current LOFAR.
To demonstrate the dynamic range, the RCU2-H prototype was connected to an HBA tile in the test field at ASTRON, and a Uniboard2. The middle figure shows the measured spectrum Note the large dynamic range, with the strong (P2000) paging signal at 169.65 MHz still a factor 10 000 (40 dB) smaller than the limit of the receiver. To demonstrate that we did not sacrifice sensitivity, the bottom figures show the galactic noise as it drift through the tile beam pointing towards zenith.
The RCU2-L board, presented in the previous newsletter, has successfully passed its DDR. We are processing some modifications and prepare additional tests to make it ready towards the first integrated (ADC+RCU) acquisition model for integration in the new subrack and, ultimately, the Dwingeloo Test Station.
Preparation for the Dwingeloo Test Station
The Dwingeloo Test Station (DTS) will be a setup of a real subrack in a LOFAR cabinet that has been placed in the test field at ASTRON. At this moment, several people are finishing connecting the cabinet with power and fiber so we can start equipping it. A standard subrack has been ordered and will be assembled. The boards to equip it will be produced locally at ASTRON in the coming weeks. The design of the two new UB2c’s are almost finished, and then these will be sent to Neways for a first production test. We expect that these should arrive back at ASTRON around March 2021.
The subrack will contain a small number of real components (RCU2L/H’s, UB2s) , augmented by ‘dummy’ boards that will use heat resistors to mimic the actual power dissipation and heat production of the final cabinet. The ‘real’ RCU2s will be connected to a small number of LBA and HBA antennae in the test field. We will also install the supporting infrastructure of a real station (power supplies, White-Rabbit clock system, LCU, switches, etc.) and set up a connection to CEP in Groningen.
The goal of the DTS is to test the integration of all of these components as early as we can in a realistic test environment. This enables us to find integration issues at this early stage, when they can still be adapted easily.
Control firmware and software
The program board has decided that Tango-Controls will be the Monitor and Control software framework. As a result of that, the effort in the Station Control work package has been directed to getting more acquainted with this technology and more connected to the Tango-Controls community. Expert help from INAF is available to make the right choices, and an INAF-funded 1FTE software developer will start early 2021 to strengthen the work package team. For those interested in helping this effort, an additional job advertisement for a software developer has been put on the ASTRON jobs site and on LinkedIn.
In the SDP work package, the last bits are being put into place for the subband correlator functionality. An interesting new development is that SDP will try to implement the data distribution ring functionality in the firmware using OpenCL, instead of VHDL. If this attempt will succeed, it will be a first for ASTRON to have an OpenCL application in firmware In a production system. Reinier van der Walle will do the implementation on behalf of the Triple-A 2 project by John Romein. Experience at other institutes, such as CERN, show that development time of firmware drastically decreases with OpenCL as compared to VHDL, so this is an interesting pilot project for ASTRON.
Finalizing the first set of ICDs (Interface Control Document) between the system components identified in the Product Breakdown Structure takes much of the effort. Especially the ICDs with Station Control are used to steer and prioritize the software development effort. As the system’s functionality will grow, so will the ICDs. Also, they are input for the test plans that are developed to show the compliancy with requirements, so these products are important for the project.
The Timing Distributor project will deliver a central clock for the LOFAR stations in the Netherlands by the end of 2021. The team is currently working at full speed to prepare for the Critical Design Review, planned for April 2021, that will mark the end of the development phase. After CDR, the project will focus on tendering, procurement, commissioning and rollout. Towards the end of 2020, the project team will reach a conclusion about the optics to be chosen (BiDi or DWDM). To allow this decision, intensive testing has been performed in the past months, both in the lab and in the field. The pictures below show the laboratories that the engineers in our team have improvised at their homes, to continue working despite Covid-19. In both pictures the White Rabbit switches can be seen together with the settings needed to take the measurements.
For this newsletter we have a very good news to share: LOFAR4SW was granted an extension by the European Commission; we can officially continue with the new proposed planning that will bring the project to an end in February 2022 (instead of May 2021 as originally proposed). This extension was requested to account for the Covid-19 delay suffered during 2020. The decision comes timely before the end of the second reporting period. During the coming months November-January the consortium will spend considerable effort to prepare the report to the funding agency.
As part of our recent activities, in October 14 LOFAR and LOFAR4SW featured prominently at the online workshop organised by ESA’s SWE Service Network with a session dedicated to “LOFAR and space weather” convened by our project scientist Maaijke Mevius by invitation of ESA. The session had experts in the different domains: Solar, Heliosphere, and Ionospheric research and was attended by about 20 people. LOFAR4SW was also present at the European Space Weather Symposium held online in November 2-6.
Meanwhile the project team continues preparing for the Critical Design Review (September 2021); the panel of reviewers is now complete and includes a mixture of scientists and engineers from different institutions, including ASTRON.
Phase 2 of the COBALT2.0 has made excellent progress since the last update. We have completed implementation of several new features that are, at the time of writing, ready to be merged into the LOFAR master repository in preparation of commissioning.
We have implemented a new redigitisation method that reduces data volumes for beamformed observations and allows us to form more tied-array beams within the available bandwidth to our storage cluster. This includes the necessary modifications to the LOFAR Data access Layer library. We have also completed the implementation of improved Doppler correction. With the addition of longer baselines to the international LOFAR array, we started to experience increasing decorrelation, which is mitigated by this correction.
We have also spent significant effort to improve our understanding of the performance of various parts of the COBALT software and wrote tests to make those visible and testable. This is a key step on our way to automatically test and integrate the COBALT code in the future.
COBALT now also includes a truly flexible beamformer pipeline that has the ability to run a correlator and several beamformer pipelines concurrently. This is a key part of the LOFAR Mega Mode, which enables generating data products for various science cases in a single observation.
All of these features are about to be merged into the LOFAR master repository, which will start the commissioning process. A commissioning procedure has been developed that combines the desire to have newly developed features made available for expert use, with the need to have these rigorously tested and scientifically validated.
ASTRON is developing TMSS (Telescope Manager Specification System), which is a brand-new software application for the specification, administration, and scheduling of LOFAR observations. It will enable the required support for LOFAR2.0 use cases, while also streamlining LOFAR operations and improving the adaptability and maintainability of software for future extensions.
The web interface of the new system is rapidly taking shape (see figures). We can now create full scheduling units and view these on a timeline in a very user-friendly way, which directly meets the needs of operations. Moreover, for convenience we can create a complete set of scheduling units in one screen. Eventually, the framework for dynamic scheduling, a revolutionary system that will automatically determine the observing schedule, is now in place. A test version has been installed in October and was successfully used in the first commissioning observations.
Two current focus areas for the further development are including a quality assessment workflow in TMSS, which will streamline the reporting of observations to the project investigators, and adding the full set of scheduling constraints to the dynamic scheduler. During the next LOFAR software roll-out in November we will connect TMSS to the production system. The development plan of TMSS is right on track: TMSS will be put in production in June 2021, at the start of cycle 16.
LOFAR is the only telescope capable of ultra-low frequency (<100 MHz) imaging at high resolution. The LOFAR LBA Sky Survey (LOLSS) is the one of the two large sky surveys of the LOFAR Survey Key Science Project is currently carrying out and it aims to cover the northern sky at 42-66 MHz reaching the sensitivity of 1 mJy/b and the resolution of 15 arcsec.
Over the past years we developed a series of techniques to correct ionospheric and beam induced direction dependent errors to finally achieve thermal noise at these frequencies. Currently the SKSP has prepared a preliminary data release with direction independent error correction covering the HETDEX field at 4 mJy/b sensitivity and 40 arcsec resolution (the mosaic and catalogue are already available for scientific exploitation within the LOFAR community). The final release at full depth and resolution of that region will follow in 2021.
With 1000 hours awarded in the last long term proposal cycle, the LOFAR LBA Sky Survey will cover next all fields above declination 40 deg. Given the strong correlation between the solar cycle and the ionospheric disturbances, we are currently rushing to collect as much data as possible before the increase of solar activity, that will prevent high dynamic range LBA imaging for an extended period of time.
The LOFAR LBA Sky Survey will provide a unique dataset to hunt for high redshift galaxies and quasars as well as for the emission from the magnetosphere of exoplanets. The survey will also enable the tracing of the oldest populations of cosmic rays in galaxies, clusters of galaxies and from AGN activity. Providing the lowest frequency information on radio spectra, the survey will also probe absorption processes that alter the power-low synchrotron spectrum at these frequencies.