SF6 Gas Replacement in Pulsed High Voltage Coaxial Cables

Several fast pulsed high voltage kicker systems at CERN use coaxial cables with SF$_6$ gas as dielectric. Leak detection systems are installed and for interventions, the gas is recuperated and re-circulated, reducing emissions to a minimum. Nevertheless due to the high global warming potential of SF$_6$ gas and the efforts of the European Union and CERN to reduce fluorinated greenhouse gas emissions to a minimum, a replacement strategy for the SF$_6$ gas filled coaxial high voltage cables is being developed. New pulse generator technologies as well as different SF$_6$ gas substitutes and also new conventional PE insulated cables are being studied. This paper gives an overview of the studies carried out to replace these cables. A comparison of possible alternatives with liquid, solid and gas dielectrics is given. The properties of the cables with alternative dielectrics are outlined, by either measurement, simulation or calculation. Especially the important parameters for kicker systems are evaluated and compared: breakdown voltage, low attenuation and low impedance change. Possible dimensions and tolerances are given, the expected costs and environmental impact are outlined. In addition an overview of different dielectric liquids used in the complete pulse generator as well as the operational experience, performance and limitations is given.