Multipactor suppression in dielectric-assist accelerating structures via diamondlike carbon coatings

Multipactor discharges are widely observed in the accelerator field, and their suppression has been studied to improve accelerator performance. A dielectric-assist accelerating (DAA) cavity is a standing-wave accelerating cavity that attains a Q-value of over 100,000 at room temperature by using the reflection of the dielectric layer; the DAA cavity is expected to be used with a small RF power source and high-duty operation. Thus far, the maximum accelerating field of DAA cavities has been limited to a few MV/m by the multipactor. By applying a diamond-like carbon (DLC) coating to reduce the secondary electron emission coefficient without sacrificing the Q-value of the cavity, we have demonstrated that a $6~[{\rm \mu s}]$ RF pulse can be injected into a DAA cavity with a field of more than 10~[MV/m] while suppressing the multipactor.