Prototype Inductive Adders With Extremely Flat-Top Output Pulses for the Compact Linear Collider at CERN

The compact linear collider (CLIC) study is exploring the scheme for an electron–positron collider with high luminosity and a nominal center-of-mass energy of 3 TeV. The CLIC predamping rings (DRs) and DRs will produce, through synchrotron radiation, ultralow emittance beam with high bunch charge, necessary for the luminosity performance of the collider. To limit the beam emittance blow-up due to oscillations, the pulse generators for the DR kickers must provide extremely flat, high voltage, pulses. The specifications for the DR extraction kickers call for a 160- or 900-ns duration flat-top pulse of $\pm 12.5$ kV, with a combined ripple and droop of not more than $\pm 0.02\%$ ($\pm 2.5$ V) for each pulse: an inductive adder is a very promising approach to meet the specifications. Recently, the first 20 layer, 12.5 kV, full-scale prototype inductive adder has been assembled at CERN and testing has commenced. This paper presents flat-top stability and repeatability measurements of the output waveforms of this full-scale prototype inductive adder for CLIC DR kicker systems. The pulse waveforms have been recorded with an oscilloscope which has nominally 16-bit resolution and allows measurements of minimum and maximum envelope curves for a large number of consecutive output waveforms. Both passive and active modulation methods have been applied to improve the relative flat-top stability of the prototype inductive adder to meet the specification of $\pm 0.02 \%$.