Development of a partition wall to prevent scattering of beam-window fragments at J-PARC Hadron Facility

A new secondary production target system for 95 kW primary proton beam in the Hadron Experimental Facility at J-PARC is now under preparation. The target made of gold is located in an airtight target chamber, which is filled up by inert helium gas at 90 kPa. The most important function of the target chamber is airtightness in order to confine radioactive materials produced and accumulated in the target. Since transportation beam line is kept in vacuum at the 1 Pa level, a beam window is necessary between the chamber and the beamline vacuum duct. Since the proton beam directly passes through the beam window, high thermal load together with gas-pressure load are applied to the beam window. In order to keep appropriate design-safety margin, we have adopted beryllium metal for the material of the beam window, as reported in the previous annual conference. However, since the beryllium is a toxic substance, a partition wall should be equipped to prevent scattering of beryllium fragments in the vacuum duct even if the beryllium window is broken. In this paper, design and examinations of the partition wall are reported. (author)