alma cloa improvements and upgrades...16 alma future science development workshop, 24-25 aug 2016 to...
TRANSCRIPT
1 ALMA Future Science Development Workshop, 24-25 Aug 2016
ALMA CLOA Improvements and Upgrades
Christophe Jacques, Bill Shillue, Jason Castro Photonic LO Group
2 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
3 ALMA Future Science Development Workshop, 24-25 Aug 2016
Current Central LO References for ALMA
AOS Central Bldg
Key
Antenna
Central Reference Generator
Correlator
Master Laser and Laser
Synthesizer
Master Frequency Standard
LO Photonic Receiver
LO Reference ReceiverCentral
Variable Reference
Line Length
Corrector
10 MHz
125 MHz
13.5—20 GHz
WDM1556 nm27-122
GHz
1532 nm, 2 GHz, 125 MHz, 48 msec
5 MHz
WDM
Buried Fiber to Antenna
48 msec
1st LO Offset
20-45 MHz 1st LO PLL ref
2nd LO ref 8-14 GHz comb2nd, 3rd LO 125 MHz
1st LO ref 27-122 GHz
`
Fiber Patch Panel
ElectronicFiber Optic
5 MHz
4 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 • 1st LO RMS integrated phase noise < 53 fs • 1st 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-15
1E-14
1E-13
1E-12
1E-11
10 100 1000
Pha
se S
truc
ture
Fun
ctio
n (s
ec)
Tau (Seconds)
Measured PhaseExpected Phase without CorrectionLO spec ALMA LO Phase
Drift over 300 seconds
5 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/sec2
Unprecedented phase stability at each antenna guaranteed vs. temperature, time, fiber length, antenna motion, …
6 ALMA Future Science Development Workshop, 24-25 Aug 2016
Current Central LO References for ALMA - 4
7 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.
8 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.
9 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.
Photonic LOV 1.0
Line Length CorrectionV. 1.0
15 km
Currrent implementation
Photonic LOV 2.0
Line Length CorrectionV. 2.0
n1 km
BidirectionalOptical amplifier
n2 km LO Regeneration n3 km
Study implementation
10 ALMA Future Science Development Workshop, 24-25 Aug 2016
Phase Drift, Visibility and Coherence • Current 1st 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)
11 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
12 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)
13 ALMA Future Science Development Workshop, 24-25 Aug 2016
Longer Baselines -2: Master Laser Coherence
X
> 50 % at 30 km
• 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
14 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
15 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.
16 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.
Photonic LOV 1.0
Line Length CorrectionV. 1.0
15 km
Currrent implementation
Photonic LOV 2.0
Line Length CorrectionV. 2.0
n1 km
BidirectionalOptical amplifier
n2 km LO Regeneration n3 km
Study implementation
17 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
18 ALMA Future Science Development Workshop, 24-25 Aug 2016
“Proof-of-Concept” bidirectional EDFA
Er doped fiber
bandpass filter
LO Signal Output
Monintor
pump/signal combiner
980 nmpump laser
5/95
Return Signal Input
Monitor
LO Signal Input
Monitor
Return Signal Output
Monintor
LO Signal (to antenna) Return Signal (from Antenna)
5/95
Allows stable LLC locking to the “equivalent” of a 70 km baseline.
19 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.
20 ALMA Future Science Development Workshop, 24-25 Aug 2016
Current Central LO for ALMA
21 ALMA Future Science Development Workshop, 24-25 Aug 2016
Elevation wrap
Azimuth wrap
Buried Fiber Optic Cable,
L<15 km
Photonic Distribution
Master Laser
4 sets of 66 Fibers
Subarray Switch
Modules
Line Length Corrector Modules
LaserSynthesizers
ML ref
1 Set of 66 Fibers
LO Photonic Receiver
WCA
WCAFRM
WCA
Band 1
Band 2
Band 9
WCABand 10
FrequencyReferences
To other Antennas
Master Laser (1556 nm)Master + Slave (1556 + 1557 nm)Electronic Signal
22 ALMA Future Science Development Workshop, 24-25 Aug 2016
Subarray Switch Line Length Corrector
LO Photonic Receiver
FRM
Band 1
Band 10
Frequency Shifter
EDFA 1:10 Switch
Compensating Fiber
LO RCVR
LO1st LO DriverYIG+Active
Multiplier Chain and PLL
Input from Laser Synthesizers
Div by N
Phase DetectorFringe CounterStretcher DriverMicroControlller
50 MHz
Fiber Stretcher Polarimeter
5 MHz ref
PBS1:6
Switch
PC
PC
“Beatnote” Det
5% PC
l sl M
FBG
WDM
1532 nm
LO Reference Receiver
WDM
48 msec
1st LO Offset
20-45 MHz 1st LO PLL ref
2nd LO ref 8-14 GHz comb2nd, 3rd LO 125 MHz
Compensating Fiber
Round-‐trip phase correc9on path in red