Scott Gerbick

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.

FRIB HWR Tuner Development

During the last two years the HWR pneumatic tuner development at FRIB evolved from the first prototypes to the final production design. A lot of warm testing and several cryogenic integrated tests with cavity were performed to optimize the tuner features. The main challenges included the bellow bushings binding and very tight space limitations for the assembly on the rail. The final design, based on the acquired experience, was prepared in collaboration with ANL and entered the preproduction phase. FIRST PNEUMATIC TUNER PROTOTYPE AT FRIB First pneumatic tuner prototype was prepared in spring 2014 (Fig.1). The design followed ANL guidelines [1]. We started the systematic study of the tuner in June 2014 using a HWR53 cavity. Figure 1: Pneumatic tuner prototype. We used FRIB LLRF controller interfaced with PC to drive the valve system and acquire helium gas pressure and frequency data. For evaluation purposes we developed 3 types of sequences:  Full range scanning with frequency and pressure registration up to 15 cycles per hour (can be executed in superconducting state and nearly critical coupling at room temperature)  Full range scanning up to 150 cycles per hour with pressure registration  Small range (1-2 psi) scanning 1800 cycles per hour with pressure registration. The pressure floor could be changed using the pressure regulator During the first warm testing runs the main part of tuning mechanism including frame, arms and cables seemed to work fine and to be under control. We only had to reinforce the planes as they were flexing and enlarge the spacing for frame to move without touching the arms. We had to concentrate on the bellows lifetime as the most critical parameter for FRIB project. We started with the bellows with 3 guides for the movable flange (Fig. 2). Figure 2: Initial bellows model. We have got one of the bellows broken in the first convolution after 500 full cycles. After that all new bellow flanges are EB welded instead of TIG to reduce the overheating and bellows damage probability, and the profile for welding had been modified. The main problem we encountered was the friction and binding between the guides and the flange. Used testing sequence consisted of about 200-300 full range cycles and about 2000 each small range cycles in at least 3 pressure regions. Several guide bar-bushing combinations and solutions were tested (Fig.3).  Nitronic bar and bushing  Nitronic bar and Bronze bushing  Nitronic bushing and Bronze bar (ANL style)  Nitronic bushing and Bronze bar of larger diameter  Nitronic/Dicronite bushing and Bronze bar  Nitronic/Dicronite bar and bushing  Nitronic/Dicronite bushing and Nitronic bar ___________________________________________ * Work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661, the State of Michigan and Michigan State University † stark@frib.msu.edu Proceedings of LINAC2016, East Lansing, MI, USA TUPLR029

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.