M. Kedzie

Superconducting 345 MHz two-spoke cavity for RIA

This paper reports development of a two-cell 345 MHz spoke-loaded superconducting cavity intended for the U.S. RIA Project driver linac. The 3 cm aperture cavity has a useful velocity range 0.3 c < v < 0.6 c. In initial tests at 4 K the prototype cavity operated cw at peak surface electric fields as high as 40 MV/m, and with 20 Watts of rf input power provides 3 MV of effective total accelerating voltage. As constructed, the niobium cavity shell was fully housed in an integral stainless-steel helium vessel using pure copper braze joints at the niobium to stainless-steel transitions.

Superconducting intermediate-velocity cavity development for RIA

This paper discusses the design and development of two types of intermediate-velocity superconducting cavity and an associated cryomodule for the RIA driver linac. The two cavity types are a 115 MHz, /spl beta//sub GEOM/ = 0.15 quarter-wave resonant (QWR) cavity, and a 173 MHz, /spl beta//sub GEOM/ = 0.26 coaxial half-wave cavity. The useful velocity range of the two cavity types extends from 0.1 to 0.4 c. Both cavities are well-corrected for dipole and quadrupole asymmetries in the accelerating field. A cryomodule is being designed to incorporate a separate vacuum system for the cavity vacuum in order to provide a clean, low-particulate environment for the superconducting cavities. This will enable a higher degree of surface cleanliness than has previously been the case for TEM-type, drift-tube-loaded superconducting cavities. The status of prototype cavity and cryomodule construction are reported.

ASSEMBLY, INSTALLATION, AND COMMISSIONING OF THE ATLAS UPGRADE CRYOMODULE

A new cryomodule containing seven low‐beta superconducting radio frequency (SRF) cavities has been added to the ATLAS heavy ion linac, providing an additional 15 MV accelerating potential to the existing accelerator. We describe the final stages of cryomodule assembly, commissioning, and installation in the ATLAS accelerator. The clean techniques used to achieve low‐particulate rf surfaces are presented, as are the module design features which enable clean assembly and reliable high‐gradient operation. The thermal performance of the cryomodule is described, along with performance data for the SRF cavities. Details on subsystem performance including helium and nitrogen systems, vacuum systems, thermal and magnetic shields, slow and fast tuners, and survey/alignment systems are given.

Design and development of a new SRF cavity cryomodule for the ATLAS intensity upgrade

The ATLAS heavy ion linac at Argonne National Laboratory is undergoing an intensity upgrade that includes the development and implementation of a new cryomodule containing four superconducting solenoids and seven quarter-wave drift-tube-loaded superconducting rf cavities. The rf cavities extend the state of the art for this class of structure and feature ASME code stamped stainless steel liquid helium containment vessels. The cryomodule design is a further evolution of techniques recently implemented in a previous upgrade [1]. We provide a status report on the construction effort and describe the vacuum vessel, thermal shield, cold mass support and alignment, and other subsystems including couplers and tuners. Cavity mechanical design is also reviewed.

A new 2 Kelvin superconducting half-wave cavity Cryomodule for PIP-II

Argonne National Laboratory has developed and is implementing a novel 2 K superconducting cavity cryomodule operating at 162.5 MHz. This cryomodule is designed for the acceleration of 2 mA H-/proton beams from 2.1 to 10 MeV as part of the Fermilab Proton Improvement Project-II (PIP-II). This work is an evolution of techniques recently implemented in two previous heavy-ion accelerator cryomodules now operating at Argonne National Laboratory. The 2 K cryomodule is comprised of 8 half-wave cavities operated in the continuous wave mode with 8 superconducting magnets, one in front of each cavity. All of the solenoids and cavities operate off of a single gravity fed 2 K helium cryogenic system expected to provide up to 50 W of 2 K cooling. Here we review the mechanical design of the cavities and cryomodule which were developed using methods similar to those required in the ASME Boiler and Pressure Vessel Code. This will include an overview of the cryomodule layout, the alignment of the accelerator components via modifications of the cryomodule vacuum vessel and provide a status report on the cryomodule assembly.

Cavities and Cryomodules for the RIA Driver Linac

We describe cavities, cryomodules, and associated subsystem concepts for the Rare Isotope Accelerator (RIA) driver linac baseline design. Some alternative concepts are also presented. Beams from protons to uranium are accelerated with superconducting RF cavities operating from 57.5 MHz to 805 MHz. Substantial cost reduction over the baseline design may be achieved by replacing three classes of elliptical cell structures operating at 2 K by two classes of three‐spoke drift tube structures. Cavity count and tunnel length are reduced while efficient cooling at 4.5 K for all linac structures may be possible. Issues include RF power requirements, microphonics, clean handling techniques, separate cavity and insulating vacuum systems, and heat load.