Cosmic ray observation at Mount Chacaltaya for beyond the knee region

We have installed a new air shower array at Mount Chacaltaya (5,200m above sea level) to observe primary cosmic rays with energies greater than 10 ¹5 eV. In our previous experiments, we measured nuclear composition of primary cosmic rays in the knee region, and showed that the average mass of cosmic ray nuclei increases with energies below and above the knee, and dominated by heavier nuclei as iron at 10¹6 eV. This result is consistent with the confinement and rigidity dependent acceleration models, and suggests that the cosmic ray origins are supernova remnants of massive population as Wolf-Rayet stars. It is of quite interest whether the mass of cosmic ray nuclei continues to increase with energies, or decreases by contributions of lighter components expected from the extra-galactic cosmic ray models. The new air shower array has been constructed in order to measure cosmic ray composition above the knee, and the detection area is larger by a factor of 100 compared to the our previous array. In this paper, we describe the characteristics of the new array.