State of the art online monitoring system for the waste beam in the rapid cycling synchrotron of the Japan Proton Accelerator Research Complex

Abstract

The 3 GeV rapid cycling synchrotron (RCS) at Japan Proton Accelerator Research Complex is already in user operation stage, delivering a stable and relatively high power beam to the Material and Life Science Experimental Facility as well as to the main ring. RCS utilizes multiturn H^{-} charge-exchange injection for which a hybrid-type boron doped carbon stripper foil known as HBC foil with a thickness of around 200 μg/cm^{2} is used at the present injection beam energy of 181 MeV. It will be changed to 290 μg/cm^{2} at the near future upgrade and design injection beam energy of 400 MeV. The stripping efficiencies are expected to be 99.6% and 99.7% in the present and the later case, respectively. The remaining 0.4% or 0.3% of the beam is called the waste beam and is transported to the injection beam dump with a capacity of only 4 kW. The full power of the injected beam at 400 MeV is 133 kW, while the waste beam power is calculated to be about 0.4 kW. The raw signal measured by a current transformer placed downstream of the waste beam dump line contains a large noise and it is practically very hard to identify the beam signal. However, a fast Fourier transformation analysis of the raw signal made it possible to clearly identify the beam signal. The power spectrum is calibrated with respect to the known injected beam current. The absolute error of the monitor system is 0.2 mV, which gives the ratio of the waste beam to the injected beam as (0.38±0.03)%. Such an accurate and realtime monitoring system provides quite an efficient method to know the conditions of the stripper foil and the incoming linac beam during the user operation.