An indigenous muon telescope to probe atmospheric, solar and Galactic phenomena

The GRAPES-3 experiment at the Cosmic Ray Laboratory in Ooty, Tamil Nadu is home to the world's largest muon telescope. It consists of nearly 4000 proportional counters, made of mild-steel square tubes of 0.1 x 0.1 m2 cross-section and 6m length each. The discovery of a transient weakening of the Earth’s magnetic shield due to space weather [1] and the first measurement of a Gigavolt potential in thunderstorms highlight the unprecedented sensitivity of the muon telescope [2]. Construction of another large muon telescope, currently under progress, is expected to enrich the physics potentials of GRAPES-3 in addressing the origin of Galactic cosmic rays, through accurate measurements of cosmic ray composition as well as enable the identification of PeV gamma-ray sources. Nearly 4000 proportional counters as required for the new muon telescope have been successfully manufactured completely in-house in the GRAPES-3 laboratory, and installed in the muon telescope. Starting with physics motivations, this talk will take you through the journey and challenges involved in making these many proportional counters in such a way they will operate in the field for at least 3 to 4 decades, along with the successful development of advanced electronics for the station.

References: 
[1]  P .K. Mohanty et al., PRL, 117, 171101 (2016).
[2]  B. Harihahan et al.,  PRL, 122, 105101 (2019).