At SOLEIL, 5 solid state amplifiers (SSA) provide the required 352 MHz CW power : 1 x 35 kW for the Booster (BO) cavity and 4 x 180 kW for the 4 superconducting cavities of the Storage Ring (SR). Based on a design fully developed in house, they consist in a combination of a large number of 330 W elementary modules (1 x 147 in the BO and 4 x 724 in the SR) with MOSFET transistors, integrated circulators and individual power supplies. After 5 years of operation, this innovative design has proved itself and demonstrated that it is an attractive alternative to the vacuum tube amplifiers, featuring an outstanding reliability and a MTBF > 1 year. In the meantime, thanks to the acquired expertise and the arrival of the 6 th generation transistors, SOLEIL has carried out developments which led to doubling the power of the elementary module (700 W @ 352 MHz & 500 MHz) while improving the performance in terms of gain, linearity, efficiency and thermal stress. This approach was also extended to frequencies from the FM to L band. The increasing interest in this technology has led SOLEIL to collaborate with several other laboratories and conclude a transfer of know-how to the French company, ELTA-AREVA.

Development of High RF Power Solid State Amplifiers at SOLEIL

Third generation synchrotron light sources are small storage rings operating in the energy range of 1.5 to 3.5 GeV. These machines require relatively low total accelerating voltage and high RF power to compensate particle beam energy losses to X-rays. Strong damping of Higher-Order Modes (HOMs) is also necessary for stable operation of high-current multi-bunch beams. Super- conducting HOM-damped single-cell cavities are ideal for such applications. Their ability to transfer almost all RF power to the beam and to operate at high accelerating gap voltages reduces the number of installed cavities thus improving overall efficiency of the RF systems. In the past many laboratories were reluctant to use super- conducting RF (SRF) technology as it was considered more complex than conventional copper accelerating structures. Proliferation of superconducting insertion devices made having a cryogenic plant the necessity for every contemporary light source thus providing infrastructure for SRF as well. With the successful and reliable operation of HOM-damped cavities at CESR and KEKB, technological developments at CERN and other laboratories and the technology transfer to industry, SRF has become the readily available technology of choice for new and small labs with no prior experience in the field. In this paper we will describe the use of superconducting cavities in fundamental RF systems and as passive structures for bunch lengthening. Operating experience and recent achievements from light sources around the world will be discussed.

/pdf/superconducting-rf-in-storage-ring-based-light-sources-5bwufa8w0v.pdf

Superconducting rf in storage-ring-based light sources *

Cavities with damped higher order modes (HOMs) are an essential ingredient for state of the art high brilliance synchrotron radiation sources to avoid degradation of the beam quality due to coupled bunch instabilities. In the last 15 years the development of such cavities has been driven by the requirements of high luminosity meson factories and only since a few years a significant design effort was made for HOM damped cavities optimised for the specific needs of storage ring based synchrotron light sources. This paper gives an overview on the design concepts of existing superconducting and normal conducting HOM damped cavities with special emphasis on a normal conducting 500 MHz cavity developed for low and medium energy high brilliance synchrotron light sources.

/pdf/hom-damped-cavities-for-high-brilliance-synchrotron-light-3qxi0g25kd.pdf

Hom damped cavities for high brilliance synchrotron light sources

Superconducting radio-frequency cavities have been chosen as the main accelerating cavities and harmonic cavities in some synchrotron light sources. The previously developed computational scheme for the multiphysics with finite-element models can be used to calculate the electromagnetic characteristics of an externally loaded cavity, but unphysical results could be found on greatly deformed cavities. To solve this problem, we mesh not only the cavity structure with shell elements, but also the cavity vacuum with solid elements at the stage of computing the structural deformation. The interior solid elements, as being assigned with a negligible rigidity, are thus adjusted to a reasonable element shape as the external loads are applied on the shell elements to simulate the real cavity structure; this deformation information is then transferred to compatible electromagnetic elements to compute the electromagnetic characteristics of the deformed cavity. Examples of this improvement are presented with a 1.5-GHz superconducting radio-frequency cavity. Two loading conditions, external pressure and longitudinal compression, are demonstrated in computing the resonance frequency.

Application of Multi-Physics Computation on Design of a Superconducting Radio-Frequency Cavity

Bunch-by-bunch feedback systems have been installed at ELETTRA to counteract coupled-bunch instabilities. Following a novel approach both the transverse and the longitudinal systems rely on the same type of programmable digital processing electronics executing the proper software. After a description of the overall machine scenario in which the transverse systems are operated, the status of the longitudinal feedback commissioning is given

Operation of the digital multi-bunch feedback systems at Elettra

In the Storage Ring (SR) of the Synchrotron SOLEIL light source, two cryomodules will provide the maximum power of 600 kW required at the nominal energy of 2.75 GeV with the full beam current of 500 mA and all the insertion devices. A cryomodule prototype, housing two 352 MHz superconducting single-cell cavities with strong damping of the Higher Order Modes (HOM) was built and successfully tested in the ESRF. Even though the achieved performance (3 MV and 380 kW) did meet the SOLEIL requirement for the first year of operation, it was decided to upgrade the cryomodule prototype before its implementation on the SR. Modifications of the internal cryogenic system as well as the input power and dipolar HOM couplers required full disassembling, reassembling and testing of the cryomodule, which were carried out at CERN. The refurbishment and test program, which was achieved in the framework of a collaboration between SOLEIL, CEA and CERN, is reported in this paper. A 2ndcryomodule, similar to the modified prototype, shall be implemented on the SR by the end of 2006.

Successful RF and Cryogenic Tests of the SOLEIL Cryomodule

Two identical cryomodules, developed at Saclay, will be assembled, tested and installed during 2002 at the 3rd generation light sources SLS and ELETTRA. Each cryomodule contains a third harmonic superconducting RF system composed by two passive 1500 MHz Nb/Cu single-cell-cavities, which were fabricated at CERN. The cryomodule components (vacuum tank, thermal shield, cold tuning system, HOM couplers) are described. Results of tests of the bare cavities in a vertical cryostat at CERN and of the complete cryomodule at CEA/Saclay are reported as well.

/pdf/super-3hc-cryomodule-layout-and-first-tests-23m1oh0r6p.pdf

Super-3hc cryomodule: layout and first tests

In both ELETTRA and the Swiss Light Source (SLS), a complementary 3rd harmonic (1.5 GHz) idle superconducting RF system has been recently implemented and commissioned, in order to lengthen the bunches and therefore improve the Touschek dominated beam lifetime. Here below we report on the commissioning results.

/pdf/first-operational-results-of-the-3rd-harmonic-6ild587huj.pdf

First operational results of the 3rd harmonic superconducting cavities in SLS and ELETTRA

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Successful RF and Cryogenic Tests of the SOLEIL Cryomodule

Super-3hc cryomodule: layout and first tests

First operational results of the 3rd harmonic superconducting cavities in SLS and ELETTRA