Atacama Large Millimeter Array Update

1
Atacama Large Millimeter Array Update

• Slides Unabashedly Stolen by
• Al Wootten
• NA ALMA Project Scientist
• From
• ALMA NA Cost/Management Review
• January 30 February 1 2006

2
The ALMA Partnership

• ALMA is a global partnership in astronomy to
  deliver a truly transformational instrument
• North America (US, Canada Taiwan in process)
• Europe (via ESO with Spain)
• Japan (now including Taiwan)
• Key Science goals include
• Image protoplanetary disks, to study their
  physical, chemical, and magnetic-field
  structures, and to detect tidal gaps created by
  planets undergoing formation in the disks
• image starburst galaxies as early as z 10
• image normal galaxies like the Milky Way out to z
  3
• Located on the Chajnantor plain of the Chilean
  Andes 16500 above sea level
• The way ALMA is being built is via a 5050
  partnership between NA Europe and a closely
  coordinated but separate effort from Japan
• ALMA will be Operated as a single Observatory
  with scientific access via regional centers
• North American ALMA Science Center (NAASC) is
  here

3
What is ALMA?

• Up to 64 12m antennas
• Plus the Compact Array of 4 x 12m and 12 x 7m
  antennas from Japan
• Baselines from 15m to 15km
• 5000m site in Atacama desert
• Receivers low-noise, wide-band (8GHz),
  dual-polarisation, SSB
• Digital correlator, gt8192 spectral channels, 4
  Stokes
• Sensitive, precision imaging between 30 and 950
  GHz
• 350 GHz continuum sensitivity about 1.4mJy in
  one second
• Angular resolution will reach 40 mas at 100 GHz
  (5mas at 900GHz)
• First light system has 6 bands 100, 230, 345 and
  650GHz
• Japan will provide 140, 460 and 900GHz
• 10-100 times more sensitive and 10-100 times
  better angular resolution compared to current
  mm/submm telescopes

4
El llano de Chajnantor
Where is ALMA?
5
Chajnantor
AOS TB
Toco
Chajnantor
Road
Negro
Chascón
Macón
OSF
Honar
43km27 miles
6
Chajnantor
V. Licancabur
Cº Chajnantor
Pampa La Bola
Cº Chascón
Cº Toco
AOS TB
Center of Array
7
OSF Facilities ALMA and Contractors Camps
ALMA Camp
Contractors Camp
Contractors Lay-down area
8
OSF Facilities ALMA and Contractors Camps
ALMA camp
Contractors recreation room
Water tanks
Contractors Dormitories
Contractors kitchen and dining room
Contractors offices
9
Recent Camp Development
Dormitories at ALMA Camp

10
Recent Camp Development
Contractors Camp dining room
11
APEX - The Atacama Pathfinder Experiment
A Vertex RSI Antenna Operating at Chajnantor

Bonn 21.10.05
R.Güsten
12
AOS Facilities
Access Road
AOS Technical Building
85 complete
13
AOS Technical Building
14
AOS TB Construction (1)
General view, January 2006
15
AOS TB Construction (2)
16
Vertex SEF grading
17
(No Transcript)
18
ALMA Status

• ALMA has just undergone a major rebaselining and
  subsequent review
• The review declared the technology readiness of
  ALMA very high and judged that most technical
  risk has been eliminated
• Five years ago ALMA was a "must do"
  scientifically but with high technical risk
  pushing the state of the art
• We now have
• prototype antennas that meet ALMAs demanding
  requirements
• receivers with near quantum-limited performance,
  unprecedented bandwidth and no mechanical tuning
• the first quadrant of the correlator completed
  below cost and with enhanced performance
• The baseline includes appropriate contingency for
  remaining technical risks (e.g. photonic local
  oscillator, highest frequency cold multipliers)

19
Front End Key Specifications(and Preliminary
Results)
ALMA Band Frequency Range Receiver noise temperature Receiver noise temperature Mixing scheme Receiver technology Responsible
ALMA Band Frequency Range TRx over 80 of the RF band TRx at any RF frequency Mixing scheme Receiver technology Responsible
1 31.3 45 GHz 17 K 28 K USB HEMT Not assigned
2 67 90 GHz 30 K 50 K LSB HEMT Not assigned
3 84 116 GHz 37 K (35K) 62 K (50K) 2SB SIS HIA
4 125 169 GHz 51 K 85 K 2SB SIS NAOJ
5 163 - 211 GHz 65 K 108 K 2SB SIS 6 units EU ?
6 211 275 GHz 83 K (40K) 138 K (60K) 2SB SIS NRAO
7 275 373 GHz 147 K (80K) 221 K (90K) 2SB SIS IRAM
8 385 500 GHz 98 K 147 K DSB SIS NAOJ
9 602 720 GHz 175 K (120K) 263 K (150K) DSB SIS SRON
10 787 950 GHz 230 K 345 K DSB SIS NAOJ ?
- between 370 373 GHz Trx is less then 300 K

• Dual, linear polarization channels
• Increased sensitivity
• Measurement of 4 Stokes parameters

• 183 GHz water vapor radiometer
• Used for atmospheric path length correction

20
Software Architecture
21
Pre-production ALMA Water Vapor
Radiometer Operating in an SMA Antenna on Mauna
Kea (January 19, 2006)
Relay mirrors
Photo courtesy of Magne Hagstrom Ross Williamson
22
System Integration Activities Prototype
Integration

• Electronics are first integrated as a system and
  characterized in the lab at AOC, Socorro.

23
Canada

• Canada is part of the North American ALMA project
• As part of this they are members of the North
  American Partnership in Radio Astronomy
• This gives them the right to compete for time
  on all NRAO facilities including ALMA
• They are delivering on of the receiver bands
  (Band 3) plus cash and software effort to an
  agreed Value of 20M FY2000
• They are also committed to providing 7.25 of the
  ALMA Operations costs
• Canada will cover all cost overruns associated
  with their work
• As such they were not part of the ALMA
  rebaselining exercise
• Canadian ALMA work is covered by an MOU which
  empowers the NA ALMA PM and the relevant NA IPT
  leads to direct their work

24
Japan

• Japanese contribution to ALMA Enhanced ALMA
• Atacama Compact Array (ACA) System
• Twelve 7-m antennas four 12-m antennas
• Higher photometric accuracy
• ACA Correlator
• high sensitivity, simultaneous realization of
  wide
• frequency coverage and high spectral
  resolution
• New frequency bands
• Band 4 (125-163GHz), Band 8 (385-500GHz), and
  Band 10 (787-950GHz) RD
• Emphasis on submillimeter wavelengths
• Contributions to infrastructure operations

25
ALMA-J plans

• Reexamine funding/Value agreements between
  projects
• Complete agreement with ALMA-J June 2006
• Respond to RFQ summer 2006
• Late 2006 3rd Executive, E-ALMA

26
Enhanced ALMA
12-m array
ACA
27
Reviews, Reviews and More Reviews
28
1.09 Science Summary Schedule
(Data from IPS as of 2006Jan13)
ATF Testing
June 06 ATF First Fringes

SEI Reference
OSF Integration Start dates
32nd
50th
1st
16th
3rd
2nd
8th
ATF Testing Support
ATF
Site Characterization
Science Support OSF
Commissioning Antenna Array Finish dates
SCIENCE SUMMARY

32nd
AOS 6 Ant Array Evaluation Complete
16th
50th
8th
Science Verification
OSF/AOS
Mar 09 Early Science Decision Point

Call for Proposals / Early Science Preparation
Jan 10 Early Science
Sept 12 Start of Full Science
29
J11485251 an EoR paradigm with ALMA
CO J6-5
Wrong declination! But High sensitivity 12hr 1?
0.2mJy Wide bandwidth 3mm, 2 x 4 GHz IF Default
continuum mode Top USB, 94.8 GHz CO 6-5 HCN
8-7 HCO 8-7 H2CO lines Lower LSB, 86.8 GHz HNC
7-6 H2CO lines C18O 6-5 H2O 658GHz
maser? Secure redshifts Molecular
astrophysics ALMA could observe CO-luminous
galaxies (e.g. M51) at z6.
30
ALMA into the EoR

• Spectral simulation of J11485251
• Detect dust emission in 1sec (5s) at 250 GHz
• Detect multiple lines, molecules per band gt
  detailed astrochemistry
• Image dust and gas at sub-kpc resolution gas
  dynamics! CO map at 0.15 resolution in 1.5 hours

CO
HCO
HCN
CCH
N. B. Atomic line diagnostics C II emission in
60sec (10s) at 256 GHz O I 63 µm at 641 GHz O
I 145 µm at 277 GHz O III 88 µm at 457 GHz N
II 122 µm at 332 GHz N II 205 µm at 197 GHz HD
112 µm at 361 GHz
31
Bandwidth Compression Nearly a whole band scan in
one spectrum
LSB
USB
Schilke et al. (2000)
32
Antenna Designs in ALMA

• Three antenna designs currently in hand
• Two will be operated in PSI interferometer in
  near future
• Vertex (APEX close copy operational at
  Chajnantor, destiny of this prototype uncertain).
• AEC (Basis of AEM design, destiny uncertain).
• MElCo prototype disassembled for retrofit to
  design similar to 3 MElCo production antennas
• Four others expected
• Production Vertex design (25-32 antennas)
• Production AEM design (25-32 antennas)
• Production MElCo 12m antennas (3 antennas)
• Production MElCo 7m antennas (12 antennas)
• For present purposes, only consider production
  Vertex and AEM designs
• As these are evolving, must assume they will be
  identical to the prototype antennas

33
Antennas

• Demanding ALMA antenna specifications
• Surface accuracy (25 µm)
• Absolute and offset pointing accuracy (2 arcsec
  absolute, 0.6 arcsec offset)
• Fast switching (1.5 deg sky in 1.5 sec)
• Path length (15 µm non-repeatable, 20 µm
  repeatable)
• To validate these specifications two prototype
  antennas built evaluated at ATF (VLA)

34
AEC Prototype Antenna
35
Vertex Prototype Antenna
36
VertexRSI and AEC Prototype Antennas
Property VertexRSI AEC
Base/Yoke/Cabin Insulated Steel Steel/Steel/CFRP
BUS Al honeycomb with CFRP plating, 24 sectors, open back, covered with removable GFRP sunshades Solid CFRP plates, 16 sectors, closed-back sectors glued and bolted together
Receiver Cabin Cynlindrical Invar thermally stabilized steel CFRP direct-connection cabin to BUS
Base 3-point support bolt connection with foundation 6-point support flanged attachments
Drive Gear and pinion Direct-drive with linear motors
Brakes Integrated on servo motor Hydraulic disk
Encoders Absolute (BEI) Incremental (Heidenhain)
Panels 264 panels, 8 rings, machined Al, open-back, 8 adjusters (3 lateral/5 axial) per panel 120 panels, 5 rings, Al honeycomb with replicated Ni skins. Rh coated, 5 adjusters per panel
Apex/Quadripod CFRP structure, configuration CFRP structure, x configuration
Focus Mechanism Hexapod (5 DOF) 3-axis mechanism
Total Mass 108 tonnes 80 tonnes
Mass Dist. (El/Az) 50/50 35/65
37
Science Implications

• Prototypes accepted from manufacturers
• Final technical evaluations complete
• Both antennas meet the specifications
• What happens with two different antenna "designs"
• common mode errors dont cancel
• But differences may help
• cost (construction, commissioning, operation)
• other ?
• Consider
• Surface differences
• Pointing
• Pathlength
• Mosaicking and polarization

38
Science ImplicationsThe Antenna Surfaces
Source AEG Results
Both telescopes easily meet specifications (lt25
µm) both are excellent antennas.
39
Prototype Pointing Results
Source AEG Results
Spec 2 all-sky 0.6 offset pointing under
primary operating conditions
40
Fast Switching
Specification 1.5 degrees in 1.5 seconds,
settling time under 3 seconds.
41
Path Length Stability
?t 3, 10, 30 minutes Wind-induced, ?t 15
minutes

• Spec 15/20 µm repeatable/nonrepeatable

42
Science Implications

• Pointing
• Both antennas meet specifications, but the
  character of pointing differs
• in compact configuration
• WIND wind "shadowing may have some effect
• SUN sunrise may have some effect
• GRAVITY both designs are essentially rigid
• in other configurations
• WIND differs over the site as will the antenna
  response
• SUN GRAVITY remain constant over the site
• Fast Switching
• Both antennas meet specifications
• Awaiting redesign of AEC quadripod
• If not, effect would be to decrease
  throughput/efficiency

43
Science Implications

• Phase / pathlength / focus
• as pointing, but a more subtle effect.
• Axis non-intersection may be the dominant effect
  on pathlength (baseline) prediction, and has no
  common mode error
• Other mechanical deformations would benefit from
  identical antennas
• Gravitational sag, thermal deformation, perhaps
  other environmental items
• Phase effects due to fiber length
• Fiber run to antenna is dominant in effective
  length change (but if monitored and corrected, no
  common mode)
• Polarization matching and primary beam shape
• determined by quadripod leg design (shadowing of
  quadripod legs, but exact shape plays a minor
  role too)
• Lesser effect from the differing arrangement of
  panels and therefore character of scattering from
  the edges

44
Fiber Length

• The effective length of the fiber is dominated by
  the run up the antenna (see ALMA Memo 443).
• Differences in the two designs include
• Length of fiber run
• Degree of thermal shielding
• Such variations are monitored and compensated.

45
Pathlength Effects

• Temperature
• Surface RMS changes with ambient temperature from
  holography
• VertexRSI 0.6-0.7 micron/K.
• AEC 0.8 micron/K.
• Both deformations had a high degree of structure
  (like BUS segment print-through for VertexRSI,
  large-scale 45-degree plus inner-ring
  print-through for AEC) probably in the noise at
  highest frequencies, where frequent calibration
  will be done in any event.
• Focal length change due to ambient temperature
  changes
• VertexRSI
• 34 micron/C from holography
• 36 micron/C from radiometry
• AEC
• 14 micron/C from holography
• 20 micron/C from radiometry
• All within specification and unlikely to impact
  science (focus tracked surface changes small)

46
Quadripods

• The optical path from the sky off the reflector
  to the subreflector intercepts the quadripod. In
  both designs, the solid angle subtended by the
  quadripod is minimized and the point of
  attachment to the antenna is as close as possible
  to the edge of the reflector to minimize
  shadowing.
• The shadowing profile is less than 1 of the
  antenna diameter.
• Owing to careful minimization of the quadripod
  profile, the sidelobes will be small and distant
  from the primary beam.
• Beam profiles were calculated from the shadowing
  profiles (next slide).
• Quadripod shadowing is known for the Vertex
  design (ALMA Antenna Group Report 40), estimated
  for the AEC design by Lucas.
• Reflections are minimized by profiling of the
  inward edge of the quadripod legs.
• Different lateral motion of the subreflectors
  with elevation in a homologous antenna could
  effect cross-polarization amenable to
  calculation.
• Shadowing is measured using holography and is the
  same for both antenna designs within a few tenths
  of a per cent.
• Integrated power lt1 of that in the main beam,
  hence sidelobe power will be more than 40 dB
  below that of the main beam.

47
Quadripod-dependent Questions
Cross
Vertex
AEC
Three sorts of interferometric baselines provide
three sorts of beams Vertex-Vertex, AEC-AEC, and
Vertex-AEC. For the most sensitive
imaging, these must all be measured and tracked.
The most sensitive images include mosaics and
polarization images.
48
Effects of Quadripod Differences

• If one ignores the effects of the sidelobes, it
  is better to have antennas with different
  configurations if you are going to correct for
  it then it is easier if they are all the same.
  James Lamb
• Case Oneno correction
• The effect of the different sidelobes is small
• Since the sidelobes differ, a source wont be in
  both at once and the effect on an image is
  diminished
• Interferometric data provide a strong
  discriminant for sources near the main beam owing
  to fringe rotation/delay offset
• Case Twocorrection applied
• Worst case is an interfering source in a
  sidelobe. But with two designs it cannot be in a
  sidelobe of all antennas at once. One will want
  to correct for the different antenna patterns

49
Summary

• If quadrupod layout is identical, advantage of a
  single design exist, but is rather limited
• ? 25 excellent antennas 25 good antennas is
  better than 50 good antennas
• ? 50 (or 64) excellent antennas is even better
• Each prototype met specifications and qualifies
  as an excellent antenna
• Conclusion The effect of having two designs for
  the 12m antennas in ALMA is small. Any imaging
  effect can be dealt with for the most sensitive
  images which might need additional care.
• Cost probably has a greater effect
• 2 designs
• 2 software interfaces
• 2 Assembly, integration, verification,
  commissioning and science verification
• 3 beams to track in the most sensitive
  applications

50

• www.alma.info
• The Atacama Large Millimeter Array (ALMA) is an
  international astronomy facility. ALMA is a
  partnership between Europe, North America and
  Japan, in cooperation with the Republic of Chile.
  ALMA is funded in North America by the U.S.
  National Science Foundation (NSF) in cooperation
  with the National Research Council of Canada
  (NRC), in Europe by the European Southern
  Observatory (ESO) and Spain. ALMA construction
  and operations are led on behalf of North America
  by the National Radio Astronomy Observatory
  (NRAO), which is managed by Associated
  Universities, Inc. (AUI), on behalf of Europe by
  ESO, and on behalf of Japan by the National
  Astronomical Observatory of Japan.