John Popielarski

New directions in superconducting radio frequency cavities for accelerators

Superconducting radio frequency (SRF) cavities used in present-day accelerators for the acceleration of charged particles near the speed of light are based on the axially symmetric TM010 mode of a pillbox cavity. Future accelerators such as the Linear Collider require high accelerating gradients to limit the length of the linac. Two techniques to improve the gradient are being explored: a cavity that is half reentrant to improve the electromagnetic characteristics, and improved heat transfer via cooling channels and surface modification at the helium interface. These changes could potentially increase the gradients and reduce the cryogenic losses. For other applications more important criteria are simplicity, acceleration of high beam current, or the ability to use advanced materials such as Nb/sub 3/Sn or high-T/sub c/ superconductors. A new type of cavity based on the TM01p pillbox mode with p>0 offers such improvements.

Cryomodule Design for A Superconducting Linac with Quarter-Wave, Half-Wave and Focusing Elements

The Rare Isotope Accelerator (RIA) driver linac is designed to accelerate heavy ions up to 400 MeV/u (β = v/c = 0.72) with a beam power up to 400 kW [1]. To obtain these intensities, partially stripped ions are accelerated in a 1400 MV superconducting linac. A design based on the 80.5 MHz harmonic requires six cavity types. A rectangular cryomodule design with a cryogenic alignment rail can accommodate all of the superconducting cavity and magnet types for RIA. A prototype 2-cavity cryomodule for the RIA elliptical cavities was designed in 2003 [2] and tested in 2004 [3]. This cryomodule design is suitable for all 3 elliptical cavity types. A similar cryomodule design has been developed for the lower-β quarter-wave and half-wave cavities for RIA. The cavities are interspersed with superconducting magnets for focusing, with 2 cavities between magnets for the quarter-wave cryomodules and 4 cavities between magnets for the halfwave cryomodules. A prototype low-β cryomodule was designed and is now under construction. The prototype module is large enough for 2 cavities and 2 magnets. The cryomodule design will be presented in this paper, along with the current status of assembly and testing of the cavities, magnets, and cryomodule.

Single crystal and large grain niobium research at Michigan State University

As Superconducting Radio Frequency (SRF) technology is used in more accelerator designs, research has focused on increasing the efficiency of these accelerators by pushing gradients and investigating cost reduction options. Today, most SRF structures are fabricated from high purity niobium. Over years of research, a material specification has been derived that defines a uniaxial, fine grain structure for SRF cavity fabrication. Most recently a push has been made to investigate the merits of using single or large grain niobium as a possible alternative to fine grain niobium. Michigan State University (MSU), in collaboration with Fermi National Accelerator Laboratory (FNAL) and Thomas Jefferson National Accelerator Facility (JLAB), is researching large grain niobium via cavity fabrication processes and testing, as well as exploring materials science issues associated with recrystallization and heat transfer. Single‐cell 1.3 GHz (β=0.081) cavities made from both fine and large grain niobium were compared bot...

FRIB Project Status and Beam Instrumentation Challenges

With an average beam power two orders of magnitude higher than operating heavy-ion facilities, the Facility for Rare Isotope Beams (FRIB) stands at the power frontier of the accelerator family. This paper summarizes the status of design, technology development, construction, commissioning, as well as path to operations and upgrades. We highlight beam instrumentation challenges including machine protection of high-power heavy-ion beams and complications of multi-charge-state and multi-ion-species accelerations.

The FRIB Superconducting Linac - Status and Plans

With an average beam power two orders of magnitude higher than operating heavy-ion facilities, the Facility for Rare Isotope Beams (FRIB) stands at the power frontier of the accelerator family. This report summarizes the current design and construction status as well as plans for commissioning, operations, and upgrades.

Design of a FRIB Half-Wave Pre-Production Cryomodule

The driver linac for the Facility for Rare Isotope Beams (FRIB) will require the production of 48 cryomodules (CMs). In addition to the =0.085 quarter-wave CM, FRIB has completed the design of a =0.53 half-wave CM as a pre-production prototype. This CM will qualify the performance of the resonators, fundamental power couplers, tuners, and cryogenic systems of the =0.53 half-wave design. In addition to the successful systems qualification; the =0.53 CM build will also verify the FRIB bottom up assembly and alignment method on a half-wave CM type. The lessons learned from the =0.085 pre-production CM build including valuable fabrication, sourcing, and assembly experience have been applied to the design of =0.53 half-wave CM. This paper will report the design of the =0.53 half-wave CM as well as the CM interfaces within the linac tunnel.

Solenoid/Magnetic Shielding Test Results in FRIB-1&2 Cryomodules

Recently we tested the first two cryomodules for FRIB, which contain β = 0.085 superconducting quarter-wave resonators and superconducting solenoid packages. Their performance was successfully validated under realistic conditions. This paper reports the solenoid package tests results.

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

FRIB Accelerator: Design and Construction Status

With an average beam power approximately two to three orders of magnitude higher than operating heavy-ion facilities, the Facility for Rare Isotope Beams (FRIB) stands at the power frontier of the accelerator family. This report summarizes the current design and construction status.

Specification and design of a 2 K helium system for cryomodule and cavity tests at FRIB

The Facility for Rare Isotope Beams (FRIB) will be a new User Facility for Nuclear Science. The facility is funded by the Department of Energy (DOE) Office of Science and Michigan State University (MSU) and will be constructed on the campus of MSU. The main accelerator for the FRIB project will be a superconducting linac constructed of 52 cryomodules, housing 344 superconducting radio frequency (SRF) cavities. All of the SRF cavities must be operated at superfluid helium temperatures of 2 K. During FRIB fabrication, and prior to the commissioning of the FRIB cryoplant, all cavities and cryomodules must be tested as part of the FRIB quality assurance program. To meet the requirements of FRIB production, upgrades to the existing SRF infrastructure at the National Superconducting Cyclotron Lab (NSCL) must be designed and commissioned. These upgrades include: two additional test Dewars, a FRIB cryomodule testing bay, and a cryogenic system capable of supporting the 2 K cryogenic load, including sub atmospheric pumps, heat exchangers, and JT valves. Transfer lines connecting these new additions will also be designed and fabricated. This paper describes these new systems and show that they will meet FRIB requirements as well as maintaining flexibility for future changes.The Facility for Rare Isotope Beams (FRIB) will be a new User Facility for Nuclear Science. The facility is funded by the Department of Energy (DOE) Office of Science and Michigan State University (MSU) and will be constructed on the campus of MSU. The main accelerator for the FRIB project will be a superconducting linac constructed of 52 cryomodules, housing 344 superconducting radio frequency (SRF) cavities. All of the SRF cavities must be operated at superfluid helium temperatures of 2 K. During FRIB fabrication, and prior to the commissioning of the FRIB cryoplant, all cavities and cryomodules must be tested as part of the FRIB quality assurance program. To meet the requirements of FRIB production, upgrades to the existing SRF infrastructure at the National Superconducting Cyclotron Lab (NSCL) must be designed and commissioned. These upgrades include: two additional test Dewars, a FRIB cryomodule testing bay, and a cryogenic system capable of supporting the 2 K cryogenic load, including sub atmospheri...