ANL, Argonne, Illinois, USA
We have designed, fabricated and tested two new half-wave resonators following the successful development of a series of niobium superconducting quarter-wave cavities. The half-wave resonators are optimized for β = 0.11 ions, operate at 162.5 MHz and are intended to provide up to 2 MV effective voltage for particles with the optimal velocity. Testing of the first two half-wave resonators is complete with both reaching accelerating voltages greater than 3.5 MV with low-field residual resistances of 1.7 and 2.3 nΩ respectively. The intention of this paper is to provide insight into how Argonne achieves low-residual resistances and high surface fields in low-beta cavities by describing the cavity design, fabrication, processing and testing.
ANL, Argonne, Illinois, USA
A superconducting higher-harmonic cavity (HHC) is under development for the Advanced Photon Source Upgrade based on a Multi-Bend Achromat lattice. This cavity will be used to improve the Touschek lifetime and the single bunch current limit by lengthening the beam. A single-cell 1.4 GHz (the 4th harmonic of the main RF) cavity is designed based on the TESLA shape. Two adjustable fundamental mode power couplers are included. The harmonic cavity voltage of 0.84 MV will be driven by the 200 mA beam with a bunch length of >50 ps RMS. Higher-order modes (HOM) must be extracted and damped. This will be done with two silicon carbide beamline HOM absorbers to minimize heating of RF structures such as the superconducting cavity and/or couplers and suppress possible beam instabilities. The HHC system is designed such that 1) most monopole and dipole HOMs are extracted along the beam pipes and damped in the ‘beamline’ silicon carbide absorbers and 2) a few HOMs, resulting from introduction of the couplers, are extracted through the coupler and dissipated in a room temperature water-cooled load. We will present time and frequency domain simulation results and discuss damping of HOMs.
THPB073
ANL, Argonne, Illinois, USA
A superconducting higher harmonic cavity (HHC) is under development for Advanced Photon Source Upgrade based on a Multi-Bend Achromat lattice. The HHC improves the Touschek lifetime and the single bunch current limit by lengthening the bunch. A TESLA-shaped single-cell 1.4 GHz (4th harmonic of the main RF) cavity will be used. Monopole and dipole higher order modes (HOMs) will be extracted primarily along the beam pipes and damped in a pair of ‘beamline’ silicon carbide (SiC) HOM dampers. These water-cooled SiC dampers will be placed just outside of the cryomodule. Maximum power dissipation in both SiC HOM dampers is estimated to be 1.7 kW at the beam current of 200 mA total and 4.2 mA max/bunch with the bunch length of RMS >50 ps. The SiC cylinder is cooled by a precision fit copper sleeve with water cooling channels. The thermal contact conductance at the interface between SiC and copper has been experimentally measured. In this paper, we will present design details of the SiC HOM dampers and experimental results of the thermal contact conductance at the interface.
ANL, Argonne, Illinois, USA
RadiaBeam, Santa Monica, California, USA
AES, Medford, New York, USA
A pair of 20 kW CW adjustable RF power couplers optimized for 1.4 GHz have been designed and are being built as part of the APS-U bunch lengthening system. The system uses one superconducting RF cavity to be installed into the APS Upgrade electron storage ring and will provide a tremendous practical benefit to the majority of users by increasing the beam lifetime by 2-3 times. The 80 mm diameter, 50 Ω coaxial couplers include 4 cm (~20 dB) of adjustability. This allows optimization of bunch lengthening for a range of storage ring beam currents and fill patterns while, simultaneously, maintaining the required 0.84 MV harmonic cavity voltage. To provide bunch lengthening, the cavity/coupler system must extract RF power (up to 32 kW) from the beam. Each coupler will transmit roughly half of the total extracted power to external water-cooled loads. The design extends upon on a well-tested ANL two RF window concept, using a pair of simple rugged 80 mm diameter alumina disks. A new feature is the ‘hourglass-shaped’ inner conductor chosen to maximize transmission at 1.4 GHz. Results of electromagnetic and thermal simulations, as well as, prototyping and initial RF testing are presented.