Secondary electron emission yields from the J-PARC RCS vacuum components

The J-PARC 3 GeV rapid-cycling synchrotron (RCS) is required to provide 1 MW pulsed protons to the spallation neutron target and the 50 GeV main ring. Since the acceleration period is set at a repetition rate of 25 Hz, the eddy current effect due to such rapid repetition magnetic field is a big issue (i.e., the perturbation of the magnetic field and the heating owing to the ohmic loss) in the metal duct. Therefore, we choose the ceramics duct in the magnets in order to avoid the eddy current effect. But the total secondary electron emission yield (SEY) from the ceramics surface is larger than the metal one and there is a possibility of bringing about the beam instability by those secondary electrons. In order to reduce these undesirable electron emission from the chamber surface, titanium nitride (TiN) is coated on the inside surface of the chambers. We measured SEY from TiN coating surface with various conditions. First, we varied the nitrogen density and crystal face in the coating. Second, we exposed the samples to the oxygen and the water vapour with electron beam bombardment in order to simulate the actual conditions. We further investigate diamond-like carbon coating to search for the possibility of another coating. The results of these measurements are shown.