Initial measurements on a prototype inductive adder for the CLIC kicker systems

The CLIC study is exploring the scheme for an electron-positron collider with high luminosity and a nominal centre-of-mass energy of 3 TeV. The CLIC pre-damping rings and damping rings will produce, through synchrotron radiation, ultra-low emittance beam with high bunch charge. To avoid beam emittance increase, the damping ring kicker systems must provide extremely flat, high-voltage, pulses. The specifications for the extraction kickers of the DRs are particularly demanding: the flattops of the pulses must be ±12.5 kV with a combined ripple and droop of not more than ±0.02 % (±2.5 V). An inductive adder is a very promising approach to meeting the specifications. To achieve ultra-flat pulses with a fast rise time the output impedance of the inductive adder needs to be well matched to the system impedance. The parasitic circuit elements of the inductive adder have a significant effect upon the output impedance and these values are very difficult to calculate accurately analytically. To predict these parameters, the 3D geometry of the adder stack and its primary circuits has been modelled using FastHenry simulation code. Recently, a five layer prototype has been built and measurements have commenced. The parasitic elements of the primary and secondary circuits of the prototype have also been measured and these values are compared with predictions. In this paper, initial results of the measurements are described and conclusions are drawn concerning the design of the prototype inductive adder.