CLUSTER: A high-frequency H-mode coupled cavity linac for low and medium energies

An innovative linear accelerating structure is proposed which is particularly suited for low-current hadrontherapy applications but can also conveniently substitute the conventional proton linacs at present considered for Accelerator Driven Systems and neutrino and muon factories. Its two main features are compactness and good power efficiency at low–medium beam velocities (0.05⩽β⩽0.5). The first is achieved through a high working frequency and a consequent high accelerating gradient, the second is obtained by coupling several H-mode cavities together. The structure was dubbed CLUSTER for “Coupled-cavity Linac USing Transverse Electric Radial field”.To compare the performance of this structure with other hadrontherapy linac designs involving high frequencies, a conceptual study has been performed for an operating frequency of 3 GHz. Moreover, a proof of principle has been obtained through RF measurements on a prototype operating at 1 GHz.An accelerator complex using a CLUSTER linac is also considered for protontherapy purposes. This total accelerator complex, called “cyclinac”, uses a commercial cyclotron as an injector to a high-frequency and high-gradient linac.