Baikal neutrino telescope NT200+ : Upgrade of data acquisition and time calibration systems

Abstract

The Baikal neutrino telescope NT200, operating since 1998, has been upgraded in spring 2005 to NT200+. This telescope with 3 additional outer strings at 100 m radius from the center encloses a geometric volume of 5 Mtons. We describe the modernized data acquisition and control system, which allows for higher bandwidth, full multiplexing of data and control streams over a single cable to shore, redundant system components and underwater data pre-processing. To calibrate all time offsets between new distant strings and the central telescope on the nsec-scale, a new external laser unit with a powerful N2-Dye laser and a light diffusor, has been developed. This laser is also used to tune reconstruction techniques for pointlike showers with energies from 20 TeV to 10 PeV.