[en] The SNS linac contains superconducting cavities with phase velocities .61 and .81 for the acceleration of H- ions. Each of the 6-cell cavities, resonant at 805 MHz at 2 degrees K, is powered by a 550 kW pulsed klystron via a coaxial coupler. The specifications for the coupler require that it withstand the full klystron power in full reflection for the duration of the RF pulse (1.3+1.5(decay) ms) at a repetition rate of 60 pps, with an average power of 48 kW. The coupler must provide a Qext of 7.3 x 105 for the medium beta and high beta cavities, respectively. A design derived from proven experience at other laboratories (primarily at KEK, for Tristan and KEK-B cavities at 508 MHz) has been adopted for the production of the 50 omega prototype couplers. The couplers include a planar coaxial window with matching compensation elements, cooled by conduction via a water system from the air side of the inner conductor. The coupler's outer conductor between the window and the cavity is actively cooled by a helium circuit with input at 5 degrees K and output at about 165 degrees K. Vacuum, arcing, infrared, and electron current monitoring and interlocking is done through several ports located near the window. The coaxial coupler is matched to a WR975 waveguide through a door-knob transition, also derived from the KEK design. Numerical calculations have been performed on the electromagnetic properties of the coupler and on the multipacting behavior of the coaxial line and window. A capacitor for DC bias will be used to control multipacting. The first coupler prototypes have been produced by industry and the results of the RF testing on them at room temperature will be presented

[en] All eighty-one fundamental power couplers for the 805 MHz superconducting cavities of the SNS linac have been RF conditioned and installed in the cryomodules successfully. The couplers were RF processed at JLAB or at the SNS in ORNL: more than forty couplers have been RF conditioned in the SNS RF Test Facility (RFTF) after the first forty couplers were conditioned at JLAB. The couplers were conditioned up to 650 kW forward power at 8% duty cycle in traveling and standing waves. They were installed on the cavities in the cryomodules and then assembled with the airside waveguide transitions. The couplers have been high power RF tested with satisfactory accelerating field gradients in the cooled cavities

[en] We describe the concepts and developments underway at JLab as part of the program to develop a new CW cryomodule capable of transporting ampere-level beam currents in a compact FEL. Requirements include real-estate gradient of at least 10 MV/m and very strong HOM damping to push BBU thresholds up by two or more orders of magnitude compared to existing designs. Cavity shape, HOM damping, power couplers, tuners etc. are being designed and optimized for this application. Cavity considerations include a large iris for beam halo, low-RF losses, HOM frequencies and Q's, low peak surface fields, field flatness and microphonics. Module considerations include high packing factor, low static heat leak, image current heating of beam-line components, cost and maintainability. This module is being developed for the next generation ERL based high power FELs but may be useful for other applications such as electron cooling, electron-ion colliders, industrial processing etc

[en] A test stand has been designed, constructed and commissioned for the processing of the SNS superconducting cavity fundamental power couplers. The cart is designed for insertion into a high-power (1 MW and higher) RF system at 805 MHz and it includes a complete vacuum pumping system, a bakeout control system and, in separate racks, all the controls for the RF conditioning, including interlocks, diagnostics and data acquisition systems

[en] The Spallation Neutron Source (SNS) makes use of superconducting cavities for the acceleration of negative H ions in the main linac. Two types of 6-cell Niobium cavities are used in the superconducting portion of the linac: 33 Beta=0.61 cavities and 48 Beta=0.81 cavities. Each cavity is powered via a coaxial fundamental power coupler (FPC) of a simple yet robust design. The electromagnetic design of the main components of that coupler has been modeled and some of those properties have been measured experimentally. Modeling includes impedance matching of the window and of the waveguide to coaxial doorknow transition; coupling of the coupler fields to the cavity fields; and multipacting behavior of the coaxial line and window. Various aspects of design, simulation, and testing on the coupler and cavity are presented

[en] For an ongoing high current cryomodule project, a total of 5 higher order mode (HOM) absorbers are required per cavity. The load is designed to absorb Radio Frequency (RF) heat induced by HOMs in a 748.5MHz cavity. Each load is targeted at a 4 kW dissipation capability. Water cooling is employed to remove the heat generated in ceramic tiles and by surface losses on the waveguide walls. A sequentially coupled RF-thermal-structural analysis was developed in ANSYS to optimize the HOM load design. Frequency-dependent dielectric material properties measured from samples and RF power spectrum calculated by the beam-cavity interaction codes were considered. The coupled field analysis capability of ANSYS avoided mapping of results between separate RF and thermal/structural simulation codes. For verification purposes, RF results obtained from ANSYS were compared to those from MAFIA, HFSS, and Microwave Studio. Good agreement was reached and this confirms that multiple-field coupled analysis is a desirable choice in analysis of HOM loads. Similar analysis could be performed on other particle accelerator components where distributed RF heating and surface current induced losses are inevitable

[en] High-power RF testing with peak power in excess of 500 kW has been performed on prototype Fundamental Power Couplers (FPC) for the Spallation Neutron Source superconducting (SNS) cavities. The testing followed the development of procedures for cleaning, assembling and preparing the FPC for installation in the test stand. The qualification of the couplers has occurred for the time being only in a limited set of conditions (travelling wave, 20 pps) as the available RF system and control instrumentation are under improvement

[en] Jefferson Lab has developed a prototype of the medium beta SNS cryomodule. Tests were recently performed on the module, which includes three 805 MHz cavities of beta=0.61, with coaxial power couplers and frequency tuners (mechanical and piezoelectric). The cavities exceeded accelerating gradients of 16 MV/m (design value 10.5 MV/m) with Q₀'s of about 10¹⁰ at the design field. One of the power couplers has been tested up to peak powers of over 700 kW. Results of the tests are reported in this paper

[en] Each of the 805 MHz superconducting cavities of the Spallation Neutron Source (SNS) is powered via a coaxial Fundamental Power Coupler (FPC) with a 50 Omega impedance and a warm planar alumina window. The design is derived from the experience of other laboratories; in particular, a number of details are based on the coupler developed for the KEK B-Factory superconducting cavities. However, other design features have been modified to account for the fact that the SNS FPC will transfer a considerably lower average power than the KEK-B coupler. Four prototypes have been manufactured so far, and preliminary tests performed on two of them at Los Alamos National Laboratory (LANL). During these tests, peak powers of over 500 kW were transferred through the couplers in the test stand designed and built for this purpose. This paper gives details of the coupler design and of the results obtained from the RF tests on the test stand during the last few months. A more comprehensive set of tests is planned for the near future