M. Johnson

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 the Rare Isotope Accelerator

The Rare Isotope Accelerator (RIA) driver linac will produce >400 MeV/u proton through uranium beams using many types of superconducting accelerating cavities such as quarter wave, spoke, and elliptical cavities. A cryomodule design that can accommodate all of the superconducting cavity and magnet types is presented. Alignment of the cold mass uses a titanium rail system, which minimizes cryomodule size, and decreases both the tunnel cross-section and length. The titanium rail is supported from the top vacuum plate by an adjustable tri-link, which is similar to existing Michigan State University magnet technology. A prototype cryomodule is under construction for testing 805 MHz, v/c=0.47, six-cell niobium cavities in realistic operating conditions. Details of the design and progress to date are presented.

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 cryogenic distribution system

The Michigan State University Facility for Rare Isotope Beams (MSU-FRIB) helium distribution system has been revised to include bayonet/warm valve type disconnects between each cryomodule and the transfer line distribution system, similar to the Thomas Jefferson National Accelerator Facility (JLab) and the Spallation Neutron Source (SNS) cryogenic distribution systems. The heat loads at various temperature levels and some of the features in the design of the distribution system are outlined. The present status, the plans for fabrication, and the procurement approach for the helium distribution system are also included.

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...

Cryogenic distribution for the Facility for Rare Isotope Beams

The Facility for Rare Isotope Beams (FRIB) is a new National User Facility for nuclear science funded by the Department of Energy Office of Science and operated by Michigan State University. The FRIB accelerator linac consists of superconducting radio-frequency (SCRF) cavities operating at 2 K and SC magnets operating at 4.5 K all cooled by a large scale cryogenic refrigeration system. A major subsystem of the cryogenic system will be the distribution system whose primary components will include a distribution box, the transfer lines and the interconnect valve boxes at each cryogenic device. An overview of the conceptual design of the distribution system including engineering details, capabilities and schedule is described.