Tribute to Christian David

The Radio Frequency and Linac Group is in charge of the 3 GHz - 200 MeV Linac pre-injector, the high power 352 MHz RF systems of the 6 GeV Booster Synchrotron and the 6 GeV Storage Ring, as well as the fast pulsed Injection and Extraction magnets. Since the commissioning of the ESRF Storage Ring in 1992, these systems have been improved and upgraded continuously.This contributes to the steady increase in the brilliance of the source as well as to the lowering of beam down-time and the trip rate.

In the Booster, two five-cell copper cavities are powered with 600 kW RF pulses and provide an accelerating voltage of up to 8 MV at the peak of the 10 Hz acceleration cycles. During each cycle, an electron pulse coming from the Linac is accelerated from 200 MeV to 6 GeV. Most of the accelerating voltage is required to compensate for the particle energy lost at high energy into synchrotron radiation in the bending magnets.

In the 6 GeV Storage Ring, six five-cell cavities are operated in CW at a total voltage of around 9 MV to compensate for the synchrotron radiation emitted in the bending magnets and in the insertion devices. With 5 MeV particle energy loss per turn and up to 200 mA of stored current, a total of 1 MW of RF power is transmitted through the cavities to the beam, in addition to the 300 kW dissipation in the cavity copper. Depending on the configuration, as much as 350 kW is fed into a single cavity. The cavities are equipped with two RF power couplers and fed through two waveguides in order not to exceed the maximum of 180 kW per coupler.

A total of four 352.2 MHz - 1.3 MW RF transmitters are available to power the accelerating cavities. In standard operation, one transmitter is connected to the two booster cavities, and two transmitters share the load of the six storage ring cavities. The fourth transmitter provides redundancy to guarantee continuous operation of the machine, even in case of a major equipment failure on one transmitter. Each transmitter is equipped with a 1.3 MW CW klystron.