ALMA CLOA Improvements and Upgrades Christophe Jacques, Bill Shillue, Jason Castro Photonic LO Group 1 ALMA Future Science Development Workshop, 24-25 Aug 2016
Outline • Overview of current system performance • ALMA 2030 motivation • Phase Drift, Visibility and Coherence • Longer Baselines • CLOA 2.0 2 ALMA Future Science Development Workshop, 24-25 Aug 2016
Current Central LO References for ALMA AOS Central Bldg Antenna Master LO Frequency Correlator 1 st LO ref 27-122 GHz Photonic WDM Standard Receiver 1 st LO 20-45 MHz 1 st LO 125 MHz Offset 5 MHz PLL ref Central LO 2 nd , 3 rd LO 125 MHz Reference 5 MHz 2 nd LO ref 8-14 GHz comb Reference Generator 48 msec Receiver Central 10 MHz Variable Reference Buried Fiber to Antenna Key 13.5—20 GHz Electronic Fiber Optic Master Laser Line Fiber 1556 nm and Laser Length Patch 27-122 WDM Synthesizer GHz Corrector Panel 1532 nm, 2 GHz, 125 MHz, 48 msec ` 3 ALMA Future Science Development Workshop, 24-25 Aug 2016
Current Central LO References for ALMA - 2 • Tunable LO for all ALMA bands, 27~ 122 GHz, including an extended Band 1 tuning range of 27~ 39 GHz • 1 st LO RMS integrated phase noise < 53 fs • 1 st LO phase drift < 18 fs, over 15 km (w/. active stabilization). • < 1 second fast-switching time to any frequency • 5 independently tunable SubArrays, expandable to 6 • For all 66 antennas, can already expand to 80 • 1 hour reset free operation / 24 hour polarization calibration stability 1E-11 Phase Structure Function (sec) Measured Phase Expected Phase without Correction 1E-12 ALMA LO Phase LO spec Drift over 300 1E-13 seconds 1E-14 1E-15 10 100 1000 Tau ¡(Seconds) 4 ALMA Future Science Development Workshop, 24-25 Aug 2016
Current Central LO References for ALMA - 3 • Antenna motion, a 100+ ton structure: – Azimuth: -275 to + 275 degrees – Elevation: -1.5 to 93.5 degrees – Velocity: 6 deg/sec – Acceleration: 18 deg/sec 2 Unprecedented phase stability at each antenna guaranteed vs. temperature, time, fiber length, antenna motion, … 5 ALMA Future Science Development Workshop, 24-25 Aug 2016
Current Central LO References for ALMA - 4 6 ALMA Future Science Development Workshop, 24-25 Aug 2016
ALMA 2030 motivation - 1 To enhance current ALMA Science, and allow new study fields: • Galactic and Extra-Galactic astronomy, galactic surveys, Solar Science, mapping, innermost cores of protoplanetary disks, imaging of masers in excited regions, imaging of nearby star- forming disks and star-forming galaxies, astrometry of nearby solar-type stars, … • Imaging and molecular spectroscopy of small feature size solar system objects (~10km at 10 AU): planetary moons, Kuiper Belt objects. We need improvements in array sensitivity, resolution, FOV, image quality, and calibration. 7 ALMA Future Science Development Workshop, 24-25 Aug 2016
ALMA 2030 motivation - 2 • The existing hardware was not designed to support these science enhancements. It was “delicately crafted” to meet the original specifications. • We should pro-actively identify and study which areas of the CLOA will require upgrading, and how. • …and since the CLOA must operate well past 2030, reliability of these solutions has to be on par with current system. 8 ALMA Future Science Development Workshop, 24-25 Aug 2016
Not only to realize the ALMA 2030 vision… • The current ALMA array would quickly benefit from these potential improvements in coherence, phase and calibration stability. Line ¡Length ¡ Photonic ¡LO 15 ¡km Correction V ¡1.0 V. ¡1.0 Currrent ¡implementation Line ¡Length ¡ LO ¡ Photonic ¡LO n1 ¡km n2 ¡km Correction n 3 ¡ k m Regeneration V ¡2.0 V. ¡2.0 Bidirectional Optical ¡amplifier Study ¡implementation 9 ALMA Future Science Development Workshop, 24-25 Aug 2016
Phase Drift, Visibility and Coherence Current 1 st LO overall phase noise measured (mm-wave antenna based LO • locked to Laser Synthesizer): < 53 fs for 65~122 GHz Laser Synthesizer PLL corrects phase noise to ~ 0.01 rad (< 27 fs) • During the best months of the year, the quietest time of the day, and the highest observing bands 8/9/10, is the phase noise & slow phase drift limiting the instrument, i.e. degrading array visibility ? (temporal delay/phase noise drift variations be smaller than those of the natural environment at least 95% of the time, over 300 s) 10 ALMA Future Science Development Workshop, 24-25 Aug 2016
Phase Drift, Visibility and Coherence study What are the areas of potential improvement ? • Improve the phase stability of the LS by 10 %, to regain maximum value at highest frequencies (coherence, resolution) • Reduce the LS locking time to enable more frequent LO tunings (efficiency) • Improve band-switching/phase calibration, to reduce/eliminate LS lock failures • Improve antenna-to-antenna phase stability: Line Length Corrector (bigger impact at shorter wavelengths) • Increase the dynamic range of the active phase correction system, increasing time between calibrations (efficiency) • Increase Band 1 CLOA tuning range past 39 GHz 11 ALMA Future Science Development Workshop, 24-25 Aug 2016
Longer Baselines - 1 • Multiple sources (ALMA Development Working Group, 2008, A Roadmap for Developing ALMA, Kameno-san’s presentation, 2013…) conclude that longer baselines (20, 30, 50, …300 km) would allow for improved Galactic, Extra-Galactic science (better resolution, more precise imaging, more accurate astrometry) Ex: a 32 km baseline (~double the current one) would allow an ~ 8 mas resolution @ 230 GHz – think of the HL Tau & SDP81 gravitational lens studies, achieved at 10 km But … (in addition to trenching & data transport, pad and antenna costs, snow removal and maintenance) 12 ALMA Future Science Development Workshop, 24-25 Aug 2016
Longer Baselines -2: Master Laser Coherence > 50 % at 30 km X ¡ • Reliable lock achieved at 22.5 km at the NTC (lab environment) • Fringes observed @ 86.2 GHz between an AOS and an OSF antenna, 24 km baseline (Olguin et al. 2012) This is just about the maximum that can be achieved with the current Master Laser 13 ALMA Future Science Development Workshop, 24-25 Aug 2016
Longer Baselines study • We need to find a laser with much greater coherence -OR- implement a new correction/regeneration scheme • The Line Length Correction needs a greater range (currently 4.5 mm) to be able to correct the much longer path lengths • We should look at alternative technologies to stretching fiber, to achieve greater range and speed, less polarization sensitivity (because of polarization to phase conversion) Less ¡than ¡0.4 ¡radians ¡SOP ¡change ¡ ¡for ¡540-‑degree ¡antenna ¡rota9on. ¡ ¡ ¡ SOP ¡change ¡plo<ed ¡against ¡input ¡ polariza9on ¡ 14 ALMA Future Science Development Workshop, 24-25 Aug 2016
Longer Baselines study • The Line Length Correction needs greater resolution in the fringe detector circuit, to 16 bits, to implement a finer fringe count and ultimately allow a “software only” type correction. A 50 km baseline may require it. • Direct photonic LO for the longer baseline antennas ? Maybe a hybrid system ? We propose to provide a roadmap for the technical solutions that need to be implemented before longer baselines are decided upon. 15 ALMA Future Science Development Workshop, 24-25 Aug 2016
To realize the ALMA 2030 vision… • As delivered, the CLOA is a complete, “holistically” designed system, where each element impacts phase stability, power budget, polarization change … of the entire LO. • Increasing the baseline length is NON trivial. • The team, having delivered the current state-of-the-art LO, is “wired” to look for solutions that will integrate into the existing ALMA structure, at the lowest cost. Line ¡Length ¡ Photonic ¡LO 15 ¡km Correction V ¡1.0 V. ¡1.0 Currrent ¡implementation Line ¡Length ¡ Photonic ¡LO LO ¡ n1 ¡km n2 ¡km n3 ¡km Correction Regeneration V ¡2.0 V. ¡2.0 Bidirectional Optical ¡amplifier Study ¡implementation 16 ALMA Future Science Development Workshop, 24-25 Aug 2016
Photonic LO group has a complete CLOA at the NTC 1 x MFS, CRG, CVR, ML, LS, MLD, PRD, LFRD 2 x SAS, LLC, LPR, FOW, WCA, and approx. 75 km of fiber 17 ALMA Future Science Development Workshop, 24-25 Aug 2016
“Proof-of-Concept” bidirectional EDFA Allows stable LLC locking to the “equivalent” of a 70 km baseline. LO Signal (to antenna) Return Signal (from Antenna) Er doped fiber bandpass filter 5/95 5/95 pump/signal combiner LO Signal Return Return LO Signal Input Signal Output Signal Input Output Monitor Monintor Monitor Monintor 980 nm pump laser 18 ALMA Future Science Development Workshop, 24-25 Aug 2016
www.nrao.edu science.nrao.edu public.nrao.edu ¡ ¡ The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. ¡ 19 ALMA Future Science Development Workshop, 24-25 Aug 2016
Current Central LO for ALMA 20 ALMA Future Science Development Workshop, 24-25 Aug 2016
Recommend
More recommend
