GPS Time Synchronization System for K2K

TL;DR

This paper describes a GPS-based time synchronization system achieving approximately 100 nanoseconds accuracy for the K2K neutrino oscillation experiment across 250 km, utilizing GPS signals and local clocks.

Contribution

It introduces a GPS synchronization method with dual clocks and high-resolution timing for long-baseline neutrino experiments, ensuring precise timing at both sites.

Findings

Achieved ~100 ns synchronization accuracy.

Implemented dual GPS clocks for redundancy.

Provided reliable fractional-second timing with 20 ns resolution.

Abstract

The K2K (KEK E362) long-baseline neutrino oscillations experiment requires synchronization of clocks with ~100 nsec accuracy at the near and far detector sites (KEK and Super-Kamiokande, respectively), which are separated by 250 km. The Global Positioning System (GPS) provides a means for satisfying this requirement at very low cost. In addition to low-resolution time data (day of year, hour, minute, second), commercial GPS receivers output a 1 pulse per sec (1PPS) signal whose leading edge is synchronized with GPS seconds rollovers to well within the required accuracy. For each beam spill trigger at KEK, and each event trigger at Super-Kamiokande, 50 MHz free-running Local Time Clock (LTC) modules at each site provide fractional-second data with 20 nsec ticks. At each site, two GPS clocks run in parallel, providing hardware backup as well as data quality checks.