RF characteristics of a 35 kV/2nF disk shaped ceramic capacitor with 200 mm diameter

High voltage ceramic capacitors are frequently used for the construction of injection or ejection kickers. Here the complex impedance of such a device (35 KV, 2 nF) with 30 mm wide connecting strips has been measured by means of a vector network-analyser. A first series resonance caused by the unavoidable inductance of such connecting strips was identified between 15 and 20 MHz depending on the width of these strips. Independently a large number of cavity type resonances of the pillbox- like shaped capacitor where found starting at 98 Mhz .At frequencies corresponding to these cavity type resonances the real of the impedance has a very pronounced peak and thus would make the capacitor unusable as a wide-band RF bypass. All measured data are in good agreement with theoretical models forthe two types of resonances observed.