Complex sentence: The Tandem Van de Graaff at Brookhaven National Laboratory was built in 1970 and was at the time the world's largest electrostatic accelerator facility.
Split into simpler sentences: The Tandem Van de Graaff is an electrostatic accelerator facility at Brookhaven National Laboratory. It was built in 1970, and was, at the time, the world's largest electrostatic accelerator facility.