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ALMA: The Atacama Large Millimeter Array

Link to ALMA Web site

I. General project/facility description

  1. Overview of the facility/project
    The Atacama Large Millimeter/Submillimeter Array (ALMA) is a revolutionary instrument in its scientific concept, in its engineering design, and in its organization as a global endeavor. ALMA will provide scientists with precise images of galaxies in formation, seen as they were twelve billion years ago; it will reveal the chemical composition of heretofore unknown stars and planets still in their formative process; and it will provide an accurate census of the size and motion of the icy fragments left over from the formation of our own solar system that are now orbiting beyond the planet Neptune. These science objectives, and many more, are made possible owing to the design concept of ALMA that combines the clarity of detail in images provided by a 64-antenna interferometric array together with the brightness sensitivity of a fully filled aperture.

    The challenges of engineering the unique ALMA telescope begin with the need for the telescope to operate in the thin, dry air found only at elevations high in the Earth's atmosphere where the light at millimeter and submillimeter wavelengths from cosmic sources penetrates to the ground. ALMA will be sited in the Altiplano of northern Chile at an elevation of 5000 meters (16,500 feet) above sea level. The ALMA site is the highest, permanent, astronomical observing site in the world. On this remote site superconducting receivers that are cryogenically cooled to less than 4 degrees above absolute zero will operate on each of the 64 12-meter diameter ALMA antennas. The signals from these receivers will be digitized and transmitted to a central processing facility where they will be combined and processed at a sustained rate greater than 1016 operations per second. As an engineering project, ALMA is a collection of 64 precisely-tuned mechanical structures each weighing more than 80 tons, cryogenically cooled superconducting electronics, and optical transmission of data at terabit rates--all operating together, continuously, on a site very high in the Andes mountains.

    The challenges of communicating the mission and the excitement of ALMA to the citizens who ultimately sponsor the project is a task as vital as the engineering challenges. To this end, a comprehensive program of education and public outreach is an integral part of the ALMA Project.

  2. Managing institution and organization
    The Atacama Large Millimeter Array (ALMA) is an international astronomy facility. Today, ALMA is an equal partnership between Europe and North America, in cooperation with the Republic of Chile, and is funded in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC), and in Europe by the European Southern Observatory (ESO) and Spain. In the near future, the process whereby Japan becomes a participant in ALMA, adding a compact array and receiver bands, is expected to be completed. 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) under a cooperative agreement with the NSF, and on behalf of Europe by ESO.

  3. Funding source(s)

  4. Construction history and cost
    ALMA constuction began in 2002, following four years of design and development (funded under the MREFC line).

    US ALMA Construction Budget (Millions US$ Y2000)
    Design & Dev. 2002 actual 2003 actual 2004 actual 2005 actual 2006 est. 2007 est. 2008 est. 2009 est. 2010 est. Total Const.
    32.0 12.0 28.1 42.2 41.5 39.2 37.1 34.8 27.0 14.3 276.3

    Status of major items:

  5. Operational history and cost
    Future facility: estimate only.

    NRAO/AUI is proposing a program of user support for ALMA data analysis to the NSF, along the lines of the 2000 AASC report recommendations. ALMA is expected to produce ~100 Tbytes/year of data. This exceeds the total amount of data accumulated in the HST archive in its lifetime by a factor of five, every year. Users will require resources at their home institutions, as well as the services of the North American ALMA Science Center, if they are to reduce and analyze this data effectively.

II. Technical details

  1. Specifics of telescope/instrument
    Array   Main Compact(ACA)
      Number of Antennas (N) 64 16
     Total Collecting Area (p/4 ND2) 7238 m2 915
     Total Collecting Length (ND) 768 m 132
     Angular Resolution 0.2 arcsec λ(mm)/baseline (km)  
    Array Configurations (dimension of filled area)    
      Compact: Filled 150 m 35 m
      Continuous Zoom 150-18500 m  
      Highest Resolution 14.8 km  
      Total Number of Antenna Stations 216 22
     Diameter (D) 12 m 4 × 12m + 12 × 7m
     Surface Accuracy 25 µ RMS 12m: 25µ; 7m: 20µ
     Pointing 0".6 RSS in 9 m/s wind same

    Front Ends
    (All frequency bands are dual polarization with noise performance limited by the atmosphere)

    Intermediate Frequency (IF)      
     Bandwidth 8 GHz, each polarization  
    Correlator   Main Array Compact Array (ACA)
     Correlated baselines 2016 (=64x63/2) 120
     Bandwidth 16 GHz per antenna same
     Spectral Channels 4096 per IF same
    Data Rate      
     Data Transmission from Antennas 120 Gb/s per antenna, continuous  
     Signal Processing at the Correlator 1.6 × 1016 multiply/add per second  

    + Four frequency bands required for first-light ALMA. Receivers in six additional atmospheric winders are deferred to future development.
    @ Bands supplied by Japan for main array. Japan provides all bands for ACA.

  2. New capabilities anticipated/planned in next 5-10 years
    New facility. Expected completion 2012, but partial array operations in 2008.

III. User profile

  1. % of "open skies" time
    The North American scientific community will have access to 37.5% of ALMA time (assuming all current ALMA partners, including Japan, are able to meet their commitments to ALMA construction). This time will be distributed among principal investigators at institutions in the United States, Canada, and Mexico on an "open skies" basis. The other international partners will control access to their own shares.

  2. Institutional affiliations of users
    The institutional distribution of users is expected to be at least as broad as it is at present for the VLA, except that users at European and Japanese institutions will have access to ALMA through their own ALMA Regional Centers. In a restricted call (ASAC, ALMA Science IPT, et al.) for sample proposals to be used in the Design Reference Science Plan for ALMA, 128 proposals were received from 75 investigators from a broad range of institutions.

  3. Student access, involvement, usage
    Student access to ALMA time will be encouraged and supported, as it is for other NRAO telescopes.

IV. Science Overview

  1. Current forefront scientific programs
    Future facility: NA

  2. Major discoveries (through 1999)
    Future facility: NA

  3. Science highlights of last 5 years
    Future facility: NA

  4. Main future science questions to be addressed

  5. Synergies with other major forefront facilities

  6. Unique contributions

V. Education/Outreach activities

  1. Visitor facility
    Future facility: under development
    ALMA will have a Visitor center at the Operations Support Facility at 2900m altitude. The potential audience includes the 10000 visitors to San Pedro de Atacama per month during the austral summer, plus students from San Pedro, Calama and throughout Chile's Region II.

  2. Student programs
    Summer student programs will include participation of ALMA in the programs run by NRAO for the last 45 years. There have typically been about 25 participants per year in the program, partially supported by the NSF REU program and partially supported by other NRAO funds.

VI. Documentation/website URLs

  1. URL of facility website
    The ALMA website is located at

  2. URL of EPO website
    Because ALMA is a construction project, on which expenditure of EPO funds is not allowed (by NSF MREFC rules), there is not now a specific ALMA EPO website. Some material may be found at:

  3. URL(s) of any brief overviews of project/facility
    Wootten's ALMA overview to the SPIE in July 2002:
  4. URL(s) of miscellaneous documentation

This page created and maintained for the RMSPG by Martha Haynes
Last modified: Mon Feb 7 19:11:31 EST 2005 after review by Paul vanden Bout