17/04/2019 Future VLBI systems Tasso Tzioumis| Facilities Program Director– Technologies for Radio Astronomy CSIRO Astronomy and Space Science IVTW November 2018 ATSC May 2016

Jupiter and Io as seen from Earth Why VLBI?  Resolution Atmosphere gives 1" limit without corrections which are easiest in radio Jupiter and Io as seen from Earth 1 arcmin 1 arcsec 0.05 arcsec 0.001 arcsec Simulated with Galileo photo IVTW November 14, 2018

Essential Features of VLBI systems – (issues) Widespread antennas – Baselines 100s  1000s km  Precise and stable timing critical. Synchronisation requires independent very stable reference clocks  H-masers Raw data samples required for Correlation of antenna signals Transmit baseband / voltage data  Extremely large data rates Mitigation: Only need 2-bit samples Data transport – internet changed issue  e-VLBI – real-time Mass storage disk systems available cheaply. Disk transport rare (remote antennas). Mainly on internet. Delayed or real time. Data Format Compatibility  mitigated with software correlators Simple to re-format on-the-fly OR ingest multiple formats OR use standard VDIF format Software correlators freely available and supported (e.g. DiFX) IVTW November 14, 2018

Current VLBI systems ***Are custom VLBI systems always necessary??!! Custom VLBI systems are implemented (needed?) Feeds/receivers: mainly standard telescope systems (but see VGOS systems for IVS) RF/IF chain: Standard till IF (e.g. IF of 0.5-1 GHz) Digitisation: Custom. Special h/w required. Digital processing: Custom h/w and firmware (DBE; DBBC; KVN/VSOP; LBA) FPGA based e.g. ROACH Data format: Custom. Many legacy formats. New standard VDIF. Mitigated by disks and internet access. Correlation: Custom. Software correlators. Mitigated by freely available correlators on HPC clusters (e.g. DiFX, STXC)  VLBI as special telescope sub-system Special and time-consuming setups. Difficult and disruptive to schedule. Only for “vlbi gurus”. ***Are custom VLBI systems always necessary??!! IVTW November 14, 2018

(H-maser; GPS; Freq references; UTC; ….) RF/IF System (LNAs, Cryo, RF, LO/IF) ADC system (Sampling, Digitisation) Digital system (FPGAs) Channels Packets Digital switch . Antenna systems (Drives, Feeds) Compute cluster (CPUs, GPUs) RF IF Data streams packets Timing systems (H-maser; GPS; Freq references; UTC; ….) Outputs Radio telescope signal flow block diagram Universal backend COTS systems RFSOC IVTW November 14, 2018

VLBI with modern telescope Receivers-Backends-GPUs Problem faced with Parkes UltraWideband (UWB) system Digitisation at Receiver in Focus cabin. RF/IF not easily available for VLBI system.  Need different/new VLBI systems??? BUT New telescope systems already produce data-packets in GPU cluster!! Voltage data samples transmitted to GPUs – e.g. Pulsar timing Samples tagged with precise timing (nsec) for pulsar timing! H-maser stability already for all systems. Also needed for pulsars.  Data in GPUs already VLBI-ready!! (Baseband & Timing) !!! Can use GPUs to channelise to VLBI channels Reformat to 2-bit and VDIF in software. Already connected to Disks and Internet. NO need for Special VLBI h/w or Firmware !! IVTW November 14, 2018

Huge advantages of new Systems Can access any Receiver or Band the telescope supports Potential for wide-band VLBI No need for special setups taking hours…. Just another telescope back-end mode. Easier to schedule and run. Cost reductions – no costly special VLBI systems No special maintenance. No VLBI h/w experts. Observations as per “normal” telescope operations. Natural fit to modern telescope subsystems (e.g UWB; PAF) Can adopt for current telescopes when modern receivers installed E.g. Parkes adopts UWB back-end for ALL receivers! IVTW November 14, 2018

Characteristics of New systems Front-end (Feed; RF/IF/LO) – Any of the receivers available on antenna Can use new UWB systems to cover large band ranges (6:1) UWL 0.7-4.2 GHz already at Parkes. Tsys ~20K; Planned: UWH 4-24 GHz Alternative: UWB-mid 4-16 GHz & UWB-H 15-30 GHz; share IF conversion. Use Multibeam or PAF feeds Universal back-end: ADCs and FPGAs Already available: ADCs at 4 Gsps and 6 Gsps Just available: RFSOC from Xilinx (16 ADCs+FPGAs) on 1 chip!! Commercial of the self (COTS) systems: Switches and GPUs Massive switches are getting cheap GPU clusters already available Astronomy software on GPUs (e.g Pulsars) available free in astro community (e.g Parkes package) Very large community investment in software IVTW November 14, 2018

Summary and Conclusions New telescope systems already produce data suitable for VLBI !! Synergies with other fields (e.g. pulsar observations and timing) Can leverage Receiver developments (eg UWB) to expand Freq and BW range of VLBI Rapid developments in ADCs+FPGAs  compact and simpler digital systems  NO need to always have “special” VLBI h/w and s/w at the telescopes Simpler maintenance Simpler setups and schedules. Part of normal telescope operation – just another “mode” Opportunity to move VLBI into the mainstream of telescope operations  More accessibility to VLBI technique IVTW November 14, 2018

CSIRO Astronomy and Space Science Tasso Tzioumis Facilities Program Director– Technologies for Radio Astronomy +61 2 9372 4350 Tasso.tzioumis@csiro.au www.csiro.au CSIRO Astronomy and Space Science