Subsystem components of ALMA are manufactured by responsible institutes in various parts of the world and shipped to Chile. As the number of the delivered components increases, the work of the AIV (Assembly, Integration, and Verification) team is getting hectic. This time, I will write about the activities carried out by AIV staff. The number of the AIV staff, which was 30 as of June this year, increased to 40 in November. Most of the staff members are working in 8-6 shifts for a two-week period (working for 8 days and taking 6 days off), and a half of them (about 20 people) are staying at OSF. Except some staff members, shift work turns to another team on Wednesday. Most of the staff members are Chilean engineers and technicians, but I do not have to speak in Spanish because they are fluent in English. Many of them have studied abroad in college or have working experience at foreign companies. Among the staff, there is a Chilean staff who can speak Japanese, too. He occasionally gives Japanese class for Chilean staff and I participate in it to provide some assistance and introduce Japanese culture.
Currently, the AIV team focuses mainly on the measurement and evaluation of surface accuracy and pointing accuracy of antennas, and verification of control software. For the measurement of the antenna surface accuracy, we use a method called “radio holography.” By receiving a signal at a wavelength of 3 mm from an oscillator installed on the top of the tower which is located 300 meters away from the antenna, the map of surface accuracy is calculated from the data obtained by two-dimensional antenna scanning. As measurement accuracy is required on a micron scale, we have difficulties in reducing error factors such as effect of the ground-reflected waves and fluctuation of the radio path. When conducting the holography measurement, we remove the subreflector installed at the primary focus of the antenna, and install a special receiver. To conduct this work, a worker approaches the focus by manlift as shown in Photo 1, while the equipment is pulled by a crane.
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Photo 1: Installation of the holography receiver |
This is a very delicate and stressful work, as we have to pay close attention not to damage the antenna surface throughout the work. In addition to this, we install a small optical telescope on the antenna to obtain data for pointing correction.
One of the most difficult activities is installation of the receiver front end unit into the antenna. The front end unit weighing 700 kg is lifted up to the receiver cabin to be fixed at the ceiling of the cabin. An experienced worker, who can control the handle to a several millimeters from 10 meters away, lifts the front end unit from the ground to the cabin using a construction machine called “telehandler” (Photo 2).
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Photo 2: Installation of the receiver front end unit into the antenna |
The lifted front end unit is pulled into the cabin by humans and lifted up to the ceiling with electrical forklift while conducting fine positional adjustment. As staff members are engaged in such highly-concentrated activities during the day, they spend relaxing time after dinner playing the guitar and quena and singing songs (Photo 3). When they heat up, the laboratory turns into a wild party with a strong beat of a trash can, instead of a drum.
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Photo 3: Big chorus in the laboratory |
