Complex sentence: In 1956 he established and became the first director of the Laboratory of High Energy at the Joint Institute for Nuclear Research in Dubna, where, along with Protvino, the largest circular proton accelerators in the world at their time, were constructed under his leadership.
Split into simpler sentences: In 1956 he established and became the first director of the Laboratory of High Energy at the Joint Institute for Nuclear Research in Dubna. Circular proton accelerators in Dubna and Protvino, the largest in the world at their time, were constructed under his leadership.