Beam Effects on the Cryogenic System of LEP2

The LEP collider was operated during 1996 for the first time with superconducting cavities at the four interaction points. During operation for physics it was observed that the dissipated heat in the cavities is not only a function of the acceleration gradient, but depends also on beam characteristics such as intensity, bunch length and beam current. These beam effects had not been foreseen in the original heat budget of the LEP cryogenic system. The observations indicating the beam effect and its origin are presented. The available capacity of the refrigerators demonstrates that cryogenics might become a limiting factor for the performance of the LEP collider.