[en] After the commissioning of the LEP e⁺e^- collider at CERN, its energy will be upgraded by adding superconducting (s.c.) r.f. cavities. Obviously, there is a great incentive to test a prototype s.c. LEP cavity in one of CERN's existing accelerators, before a production in series of a large number of cavities (256) be launched. Such a test should prove the validity and the long-term reliability of the design in a real accelerator environment. The SPS proton accelerator/proton-antiproton collider/LEP injector was chosen for the implementation of the cavity, being at present CERN's largest accelerator. As a result the whole experiment (comprising Cavity, cryostat, refrigerator and r.f. system, installed in the tunnel about 60 m below ground) had to be remotely controlled from the accelerator surface buildings, in order not to interfere with the physics program. As long as a refrigerator was not yet delivered (during the first phase of the experiment) we used a 100 m long flexible He transfer line for cooldown with dewars located at the surface. Later on a cold box was installed 6 m off the cryostat, the compressor and control unit being placed in a surface building. For the operation of the SPS as a proton accelerator at high intensity (I_d.c. = 0.2 A), on magnetic cycles interleaved with cycles for lepton acceleration, the impedance of the s.c. cavity had to be reduced by several orders of magnitude. This was achieved by damping the cavity's fundamental passband mode impedances by an r.f. feedback including the tetrode power amplifier driving the cavity [1,2]. 10 refs., 5 figs