In 1971, Jentschke accepted the post as Director General of CERN Laboratory I (the Meyrin site); John Adams was Director General of the neighboring CERN Laboratory II (Prévessin), where the new SPS proton synchrotron was being constructed.
Jentschke became the chief at CERN Laboratory I (Meyrin) in 1971, while John Adams led the nearby CERN Laboratory II (Prévessin), which was constructing a new SPS proton accelerator.