A wire Scanner profile Monitor (WSM) has been developed for the demonstration ring of Fixed Field Alternating gradient (FFA) accelerator, called FETS-FFA. From previous studies, Carbon Nano Tube (CNT) wire is selected for the FETS-FFA WSM, durable for the heat damage of low-energy proton beams on the FETS-FFA test ring (3-12 MeV). A bias voltage, applied to the measuring wires, is required to prevent secondary electrons from returning to the wire due to the stray magnetic fields of the FFA main magnets. The endurance tests of bias voltages on different sizes of CNTs were performed prior to the beam tests on the Front-End Test-Stand (FETS) beam line and the FFA ring at KURNS. The beam tests with bias voltages on FETS and numerical simulations revealed secondary electrons from adjacent wires degraded the reading sensitivity, hence profile accuracy, explaining why the peak of the beam profile was not proportional to the wire size in previous studies. This paper will focus on the endurance test of bias voltages on CNTs as well as beam profile measurements with bias voltages on the FETS beam line. The mechanical design of the rig to install a thin CNT wire (diameter of 10 μm) on the frame head of FETS-FFA WSM will also be presented.
Yamakawa et al. (Tue,) studied this question.