Failure mode studies of the RAON superconducting linear accelerator

The driver accelerator of the RAON is a superconducting linear accelerator consisting of low beta cavities. Studies of various failure modes are performed through extensive machine imperfection studies. It is found that the linac is tolerant of any single superconducting cavity loss except the first nine upstream QWR cavities. Studies also find that the linac design is tolerant of 10% upstream-section cavity failure with the design-beta cavities. It is also found that in case of 10% cavity failure, orbit correction becomes indispensable. On the other hand, if cavity betas of the HWR and the SSR2 increase by 4% from the design values, the linac beam loss starts to increase rapidly, when 10% upstream-section cavities become inoperable. This paper shows quantitatively that significant beam losses can be caused in case of cavity faults, when the exit energy of the upstream section is not high enough. In case of a quadrupole doublet failure in the QWR section, beam loss of about 70 W/m is generated in the immediate downstream and beam operation is not feasible.