SBIR-STTR Award

Superconducting Radio Frequency (SRF) structures used for particle accelerators typically operate between 4 – 2 K, i-e- cryogenic temperatures, and are sensitive to microphonics that create length oscillations in the accelerating structures- To keep the SRF cavities on resonance under the influence of distortions in the SRF cavities caused by microphonics, RF power above what is required for accelerating the particles is supplied to the cavities- This additional RF power is both a significant capital expense and operational expense- Boron nitride nanotube (BNNT) mats, the size of small postage stamps, have been observed to have exceptional viscoelastic behavior- Preliminary results on larger samples have demonstrated that this viscoelastic behavior is also present in the larger mats, and very importantly, this behavior is observed at both liquid nitrogen and elevated temperatures- Consequently, these novel BNNT mats are anticipated to be able to provide vibration damping for both high-temperature and low/cryogenic-temperature structures- This includes fully assembled cryo-modules with SRF cavities, their superfluid liquid helium vessels, tuners, and cryostats thereby reducing capital cost and operating expenses for particle accelerators-

Our Phase I SBIR results show that BNNT provides viscoelastic vibration damping at 2 K and 4 K. Consequently, BNNT can be utilized to significantly enhance the performance of Superconducting Radio Frequency (SRF) structures used for particle accelerators. SRF structures typically operate close to absolute zero temperature and are sensitive to microphonics that create length oscillations in the accelerating structures. To keep the SRF cavities on resonance under the influence of distortions in the SRF cavities caused by microphonics, tunable RF power above what is required for accelerating the particles is supplied to the cavities. This RF power is both a significant capital and operational expense. BNNT passive vibration damping addresses these problems by reducing length oscillations and consequently the excess RF acceleration power requirement. The Phase I results of BNNT in the form of pellets for viscoelastic vibration damping were measured in collaboration with Jefferson Lab utilizing cryogenic resources in their SRF Institute. The tests involved measuring dampened harmonic oscillator vibrations where BNNT pellets were the passive vibration damping element in a specially-built system in the Jefferson Lab vertical test area (VTA). In year one of Phase II, we will engineer components for incorporating BNNT vibration damping into an SRF cavity, and demonstrate damping while the cavity is powered with RF. In year two of Phase II, we will demonstrate damping in a full cryomodule with eight SRF cavities. Jefferson Lab is planning to upgrade or refurbish two of the CEBAF accelerator cryomodules per year. The year two Phase II work will be incorporated into one of these cryomodules. The goal is to demonstrate less lost beam time due to microphonics, and a corresponding increase in operating energy due to increase in up time of the BNNT enhanced cryomodule. Based on performance in the BNNT enhanced cryomodule, BNNT vibration damping can then be incorporated in future year’s CEBAF cryomodule upgrades. Further, with the demonstration of the BNNT enhanced CEBAF cryomodules, other accelerators in the world, including those operated by DOE, can implement BNNT pellets for vibration damping. The development of BNNT based viscoelastic vibration damping at cryogenic temperatures will find commercial applications in quantum computers, cryocooled sensors, liquified-gas plants, and transportation (e.g., liquified natural gas (LNG), liquid nitrogen (“LN”), and liquid oxygen (“LOx”). Space vehicles use liquid hydrogen, densified liquid methane, LOx, etc. and have significant vibration challenges, especially during launch, along with engine components having vibrations at very high temperatures. BNNT also provides vibration damping at temperatures in excess of 400°C. Additionally, there is a significant industry for vibration sensitive cryogenically cooled test equipment.