RF power source and distribution at 352 MHz for spoke cavities for ESS and at FREIA
Presented by Dr. Rutambhara YOGI on 8 May 2012 from 14:30 to 15:00
Session: Session 2
European Spallation Source (ESS) is one of the world’s most powerful neutron sources. The ESS linac will accelerate 50mA of protons to 2.5GeV in 2.86ms long pulses at a repetition rate of 14 Hz. It produces beam with 5MW average power and 125MW peak power. There are 36 superconducting spoke resonators, which provide a power of 0.5MW to the beam. FREIA (Facility for Research Instrumentation and Accelerator Development) in Uppsala University will develop one prototype amplifier chain. The baseline for the RF system in ESS is a point-to-point generation and distribution of the RF power from a single source to a single accelerating cavity. The capital and running cost of an accelerator is strongly affected by the r.f. power amplifiers in a number of ways. The capital cost of the amplifiers (including replacement tubes) is an appreciable part of the total capital cost of the accelerator. Their efficiency determines the electricity required and, therefore, the running cost. The gain of the final power amplifier determines the number of stages required in the r.f. amplifier chain. The size and weight of the amplifiers determines the space required and can, therefore, have an influence on the size and cost of the tunnel in which the accelerator is installed. Hence selection of power source is very important. Selection and the criteria used for selection is dealt in the present paper. Typical power sources used at 352MHz at high power are tetrodes, klystrons, IOTs, solid state amplifiers and diacrodes. The paper discusses all these topologies based on capital cost, size, efficiency, gain, power supplies and stringent requirements on specifications of power supplies, replacibility, life time and their running cost. Considering all these parameters, the tetrode has been selected as driver amplifier. The tetrode gain is relatively low, around 20 dB, and a pre-amplifier stage is required. The possible pre-amplifier topologies are solid state amplifier and triode. Both the topologies are compared based on various parameters as discussed above for the amplifier and solid state amplifiers are selected as pre-amplifier. The paper also discusses the RF distribution scheme between power source and spoke resonator.