A vision of distant worlds - ALMA RADIO TELESCOPE

The largest radio telescope in the world has been in operation for the past two years in northern Chile. ALMA, or “Atacama Large Millimeter Array”, comprises a network of 66 highly sensitive parabolic antennae which capture signals from space in the millimetre and sub-millimetre range.  

The information they deliver enables scientists to gain important insights into the nature of cosmic gas and dust clouds, which have temperatures only a few dozen degrees above absolute zero. To transmit the sensitive signals from the parabolic antennae to the central analysis unit, every antenna is equipped with cryogenic units operating on an ultra-pure helium circuit. A helium recovery system from BAUER KOMPRESSOREN helps to recover the helium in essential maintenance operations, and thus safeguards the sustaina-bility of this valuable resource. 

The site chosen for the radio tele-scope could hardly have been more extreme. The high plateau of Llano de Chajnantor lies in the harsh environment of the Atacama desert in northern Chile, 5000 metres above sea level. Temperature fluctuations of 40° C between day and night and the thin, low oxygen air present enormous challenges to peopleand materials – but these are the very climatic conditions that provide for successful operation of the telescope. The air is extremely dry and has virtually no humidity, which would mask the wave lengths between infrared and radio waves. The journey from San Pedro de Atacama to the ALMA Observatory is like travelling through a science fiction film set; a forest of white antennae co-vers the barren lunar landscape of red sand and rocks. The network of inter-connected antennae transmit the signals they receive to a central computer, where they are combined and sent to the central OSF (Operation Support Facility).  

The technical challenge is to transmit these signals with losses as low as possible. To do this, the receiver units are helium-cooled to a temperature of below 4 Kelvin (-269.15 °C). These extremely low temperatures can only be achieved by using ultra-pure helium. The flushing processes usually involved in maintenance works result in loss of helium – an extremely costly element that is in increasingly short supply. Given this and the difficulty of delivering supplies to this remote location, an alternative long-term solution was necessary. 

The ESO (European Southern Obser-vatory) decided to install a BAUER helium recovery system to make the maximum use of the precious gas. This system collects the helium in a gas bag and recompresses it to 220 bar using a BAUER VERTICUS G100-3-5 high-pressure compressor connected to a P 61 purification. Two B160 storage systems provide interim storage before the gas is reused. Given the challenging environmental conditions, the legendary reliability of BAUER KOMPRESSOREN products clinched the decision to choose a BAUER compressor system – as the onsite Technical Director, Armin Silber, confirmed in an interview at the ESO Center in Garching.