The basic elements of the TESLA linear collider with integrated X-ray FEL are superconducting accelerating cavities. The standard TESLA rf system is designed for a long (1300μs) rf pulse with a flat-top of 800μs and has several elements for the rf power distribution and protectionagainst reflected rf power. Together with the superconducting cavities, normal conducting (NC) cavities are used in TESLA for different purposes, for example as a rf gun. As a rule, one NC cavity uses the total rf

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... from one klystron (5MWor 10 MW). During the short transient period (the filling time for the L-band NC cavity is near 3μs) the reflected rf power and overvoltage in the waveguide (due to the interference of the forward and backward waves) exceeds the safety limit for the L-band waveguide operation (without SF6 filling). With a special shape of the start up of the rf pulse it is possible to reduce the reflected power several times and limit the overvoltage to a safe level. The increasing of the total pulse length is in the order of two filling times (6μs) and hence negligible in comparison with the total pulse length of 800μs. Different shapes of the beginning of the rf pulse are both considered to reduce the reflected power and to restrict the overvoltage. Results of experiments are presented.