R&D on C-band accelerators

Margarita Synanidi — Wed, 26 Nov 2014 10:35:40 +0000

R&D on C-band accelerators
by David Alesini (INFN-LNF) and Marica Biagini (INFN-LNF)

Fig1: Breakdown rates as measured at different field values before and after conditioning of the SPARC C-Band prototype. After processing, about 50 MV/m accelerating field has been reached, with a breakdown rate (BDR) per meter of the order of 10-6, which is a very good result in such structures. Image credits: INFN-LNF
Fig2: SPARC C-Band structure in the oven before brazing. Image credits: INFN-LNF

The use of Radio-Frequency C-Band accelerating structures for electron acceleration and production of high quality beams has been recently proposed and adopted in several linac projects all over the world.

Two important FEL projects have adopted such type of structures: the Japanese FEL project at SPring-8 and the Swiss-FEL project at the Paul Scherrer Institute (PSI). Even if this technology is less known with respect to the more consolidated S-Band one, beam dynamics calculations and experimental measurements demonstrated the possibility to reach high beam quality and higher gradients, making the C-Band technology very appealing from this point of view. Possibilities to use C-Band structures for hadron therapy are also under study from several years and seem to be very promising.

In the SPARC photo-injector facility at the INFN Frascati National Laboratories (LNF, Italy) an R&D programme on C-Band structures is being carried out in order to upgrade the beam energy from 150 to more than 250 MeV in the facility. Involving both LNF and PSI, this programme is performed within the High Gradient Acceleration (HGA) Work Package of the TIARA Preparatory Phase.

The choice of the C-Band for the energy upgrade was dictated by the opportunity to achieve a higher accelerating gradient, enabled by the higher frequency, and to explore C-Band acceleration combined with a S-Band injector that, from beam dynamics simulations, looks very promising. The energy upgrade of SPARC will be done by replacing one low gradient S-Band accelerating structure with two C-Band structures.

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C-band accelerating structures at SPARC

Margarita Synanidi — Wed, 17 Sep 2014 14:17:46 +0000

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.