Critical Technical Issues for SRF’s Advance

Pulsed high-energy linear accelerators (linacs) for electrons and other leptons

Examples are linear colliders like the International Linear Collider, muon colliders, and neutrino factories. These machines are characterized by large size and large numbers of components.

The critical technical issues are:

• Cost-efficient designs
• High gradient in cavities
• Consistency in the performance of cavities
• Cheap reliable power couplers
• Reliability of accelerator complex; high availability

Energy-recovering linear accelerators (ERLs)

Examples in this category include ERL-driven light sources—notably free-electron lasers like Jefferson Lab’s—and electron coolers—used to reduce the transverse emittance of stored ion beam. These accelerators are characterized by medium to large beam currents that are simultaneously accelerated and decelerated in the same cavities, so there is little net transfer of RF power between the sources and the beam. These high currents still generate large amounts of higher-order-mode (HOM) power that will need to be extracted to prevent beam instabilities. Small fluctuations in the beam properties can also cause a large random beam loading that will have to be controlled.

The critical technical issues are:

• Cavity designs for high current
• HOM mitigation and extraction
• Beam instabilities
• RF control of random beam loading; microphonics
• Halo mitigation and control

The table below, which is arranged according to beam current, illustrates the variety of challenges for the advance of SRF. The colors indicate levels of difficulty, with yellow meaning demanding, blue more demanding, and green the most demanding.