Horn Operational Experience in K2K, MiniBooNE, NuMI and CNGS

This paper gives an overview of the operation and experience gained in the running of magnetic horns in conventional neutrino beam lines (K2K, MiniBooNE, NuMI and CNGS) over the last decade. Increasing beam power puts higher demands on horn conductors but even more on their hydraulic and electrical systems, while the horn environment itself becomes more hostile due to radiation. Experience shows that designing horns for remote handling and testing them extensively without beam become prerequisites for successful future neutrino beam lines.