Thesis defence: The number of arms is ideally three or five for the LOFAR-telescope

The deeper we look into the universe, the closer we get to its origin. This fact triggers astronomers to build larger and more advanced telescopes. The Low Frequency Array (LOFAR) belongs to the newest generation of radio telescopes and is developed by the Netherlands Foundation for Research in Astronomy (ASTRON) to open the radio spectrum from 15 to 240 megahertz. LOFAR will consist of more than 100 multi-sensor stations spread out in an area of a few hundreds of square kilometers in the Netherlands and neighboring countries, connected by high-speed optical cables with a supercomputer. In this way a giant observation instrument is synthesized with high sensitivity and high resolution.

The dissertation of Lolke Schakel contributes to knowledge and insights of how to find an optimal topological design, an optimal geographical location, and an economical cabling for LOFAR. This design problem and the corresponding optimizations make use of techniques from the Operations Research, and aim to simultaneously maximize the imaging performance and minimize the construction costs of the instrument. In the research, the relevant design aspects have been integrated in a large mathematical optimization model. By varying uncertain parameters we get insights in the costs of alternative scenarios, so that an optimal trade-off can be made between the price and the quality of LOFAR.

Schakels finds from his research that the multi-armed spiral design proposed by ASTRON should be preferably built with an odd number of arms. The number of arms is ideally three or five and the arms have to be sufficiently bended to optimize the imaging performance of the instrument in snapshot mode. In that case the spiral design is near pareto-optimal. The choice for the number of spiral arms has to be made on the basis of the required imaging performance, the level of the observation robustness, the budget available for the cabling, and the speed at which LOFAR has to fully track the radio sky. The scalability of the spiral design has as additional advantages that it allows for a phased deployment and that the instrument can be easily upgraded by means of the addition of new multi-sensor stations at the end of the spiral arms or between adjacent multi-sensor stations on an arm. This property is especially useful when future budgets become uncertain.  

Curriculum vitae

Lolke Schakel (Harlingen, 1979) studied econometrics and operations research in Groningen. and conducted his PhD research at SOM research school of the Faculty of Economics and Business. He will be awarded his PhD on 16 April (2.45 pm). The supervisors are prof.dr. G. Sierksma and prof.dr. H.R. Butcher. The thesis title is: Het logistieke ontwerp van de LOFAR radiotelescoop: een operations research benadering ter optimalisatie van het waarnemingsvermogen en de bouwkosten.