CERN Accelerating science

  High power test results on C-band accelerating structures
  by David Alesini (INFN-LNF) & Marica Biagini (INFN-LNF)

  Fig1: C-Band structure installed in                                        Fig2: C-band accelerating structure under test
     SPARC for high power tests.                                                                                  Image credit: INFN-LNF

C-Band structures for the SPARC photo-injector energy upgrade have been designed, built and tested at the INFN-LNF Laboratories in Frascati (Italy).

In the SPARC photo-injector facility at the INFN Frascati National Laboratories (LNF, Italy) an R&D program on C-Band structures was being carried out in order to upgrade the beam energy from 180 to more than 250 MeV in the facility. This work was supported by INFN and TIARA Preparatory Phase EU program within the High Gradient Acceleration (HGA) Work Package.

The two C-Band structures are Traveling Wave (TW) and Constant Impedance (CI), with an integrated axial symmetric input coupler. High power tests have demonstrated the structure capability of withstanding operation accelerating gradients larger than 35 MV/m. A stable and flexible C-band digital low level RF system has been also developed by the Paul Scherrer Institute and integrated in the SPARC control system. The RF conditioning for the first RF structure lasted about 10-15 full equivalent days. As a result, it reached 38 MW input power in the structure (44 MW from the klystron) at a nominal repetition rate and pulse length. The corresponding accelerating field was 36 MV/m peak and 32 MV/m average, the BreakDown Rate, not yet measured, is expected to be lower than 10-5. Finally, the modulator voltage was 340 kV. The RF conditioning of the second RF structure was concluded in February 2014 with similar results.