Design of the FRIB Cryomodule Page: 2 of 3
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Proceedings of IPAC2012, New Orleans, Louisiana, USA
Table 2: Alignment Requirements for Cryomodule
Component to Beam [mm a
Resonator +2a =11 mm +2a =+2 mm
SC Solenoid 2a =+1 mm +3a =13 mm
BPM 2a = 1 mm +2a = 1 mm
The cryogenics sub-system requires independent
helium circuits for the resonators at 2 K and SC solenoids
at 4.5 K. The two circuits allow magnetic degaussing
cycles to be performed on the solenoid to remove
magnetic fields while the resonators are raised above
niobium's superconducting transition temperature via
heaters. A third helium circuit is required for efficient
cryogenic operation by intercepting heat conduction and
radiation pathways. This third circuit supplies helium at
38 K to minimize cryoplant plug in power load .
An overall attempt was made to incorporate design for
assembly and manufacture methods to reduce the number
of parts, optimizing assembly time and material usage.
Where practically possible the design has been optimized
for minimal parts and designed for multiple functions.
Accelerator robustness requires a spare cryomodule to
be substituted by use of a modular interface to the
cryogenics distribution without requiring warm up of a
To reach maximum resonator Qo a magnetic
environment for the resonators of 15 mG has been chosen
as the cryomodule requirement.
RF power requirements are delivered to the resonators
via a co-axial fundamental power coupler (FPC).
Delivery is made below the vacuum vessel that interfaces
to the internal resonator string.
Safety requirements for the cryomodule cover
assembly, operation and maintenance. Failure scenarios
of beam line or insulation vacuum require adequate
pressure reliefs. The helium vessels and cryogenic
system are designed according to the ASME BPV and
ASME 31.1 piping code.
Ability to transport the cryomodule at an offsite
location beyond the FRIB facility allows potential cost
savings. A transport acceleration requirement of 6 g
vertical, 2 g lateral and 5 g longitudinal was used [2,3].
To meet requirements, the FRIB cryomodule consists of
five sub-systems: cold mass, cryogenic, thermal radiation
shield, magnetic shield, and vacuum vessel.
The resonators and solenoids are assembled to a
support structure made from #316 stainless steel (UNS
S31600) that is divided longitudinally into 3 pieces to
minimize static deflections. This support structure holds
the resonator and solenoid components during room
temperature assembly and cryogenic operation. The
interface between the cryogenic support structure and the
room temperature bottom plate structure is composed of
g-10 posts. The room temperature end of the composite
posts rests on precision linear rails which are pointed to
the center of thermal contraction. This design allows a
low friction, high precision assembly using
interchangeable parts that are machined to standard
geometric tolerances. The reinforced bottom plate
functions as a support platform for the resonator string,
cryogenic sub-system, and is also an integral vacuum
The transverse alignment requirement is 2a = +1 mm.
Alignment requirements are met using a machined to
tolerance approach as done at Cornell . Component
drawing specifications using geometric dimensioning and
tolerancing results in a worst case tolerance stack-up
scenario of +0.87 mm.
The resonators are housed in a commercially pure
grade 2 titanium helium vessel. The half wave resonators
are maintained on operating frequency via a scissor jack
tuner made of #316 stainless steel (UNS S31600) with an
external stepper motor and gearbox. The HWR vessel is
compliant to accommodate the tuning displacement where
the QWR has a stainless steel formed bellows tuner
interface on the resonator bottom. RF power is delivered
to all resonators via coaxial RF lines.
The cold mass sub-system is assembled in a class 100
clean room similar to the SNS cold mass assembly
process to minimize particulate contamination . The
required assembly and transport from the class 100 clean
room utilizes the same support structure made from
#316L stainless steel (UNS S31603) used for alignment
minimizing total required components.
The approach to satisfy cryogenic requirements started
by consideration at a project wide level and approaching
it as an all-encompassing system composed of the
cryogenic plant, distribution system and cryomodules.
Present work at JLAB for FRIB in 2 K process
improvements is expected to yield efficiency gains that
will be incorporated into the FRIB cryomodule. The
independent 2 K and 4.5 K helium flow schematic is
shown in figure 2. Joule-Thompson valves incorporated
into the cryomodule produce liquid from the 3 ATM 5 K
supercritical helium supply. To minimize the heat
conduction a 4.5 K heat station is incorporated via a
thermo-syphon loop from the 4.5 K circuit. A second
heat station uses helium gas supply at 38 K and returned
to the plant. The interface between the cryogenic
distribution line and the cryomodule is a set of 5 U-tube
bayonet connections shown in figure 3.
07 Accelerator Technology and Main Systems
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Johnson, M J; Binkowski, J; Bricker, S; Casagrande, F; Fox, A D; Lang, B R et al. Design of the FRIB Cryomodule, article, July 1, 2012; Newport News, Virginia. (digital.library.unt.edu/ark:/67531/metadc839027/m1/2/: accessed November 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.