Design of 162-MHz CW Bunch-by-Bunch Chopper and Prototype Testing Results

The PIP-II program of upgrades proposed for the Fermilab accelerator complex is centered around an 800 MeV, 2 mA CW SRF linac. A unique feature of the PIP-II linac is the capability to form a flexible bunch structure by removing a pre-programmed set of bunches from a long-pulse or CW 162.5 MHz train, coming from the RFQ, within the 2.1-MeV Medium Energy Beam Transport (MEBT) section. The MEBT chopping system consists of two travelling-wave kickers working in sync followed by a beam absorber. The prototype components of the chopping system, two design variants of the kickers and a 1/4-size absorber, have been installed in the PIP-II Injector Test (PIP2IT) accelerator and successfully tested with beam of up to 5 mA. In part, one of the kickers demonstrated a capability to create an aperiodic pulse sequence suitable for synchronous injection into the Booster while operating at 500 V and average switching frequency of 44 MHz during 0.55 ms bursts at 20 Hz. This report presents the design of the PIP-II MEBT chopping system and results of prototypes testing at PIP2IT.