Boron Nitride Nanotube Vibration Damping for SRF Structures

Controlling microphonics that create length oscillations in the structures that accelerate particles in Superconducting Radio Frequency (SRF) accelerators requires costly RF power for both capital and operating expenses above what is otherwise required for accelerating the particles. Passive viscoelastic vibration damping at cryogenic temperatures of 2 Kelvin (K) provided by our boron nitride nanotubes (BNNT) provide a cost-effective alternative to enhance management of the microphonics. Our SBIR Phase I successfully proved the soundness of this approach. Since then, our in-progress SBIR Initial Phase II has already successfully proven BNNT vibration damping in both SRF cavities of the pair in which it was installed, in a pre-shipment SLAC LCLS-II cryomodule at 2 K and intends to further prove similar vibration damping in a Jefferson Lab C100 cryomodule cavity pair in the horizontal test bed (though delayed by JLab amid pandemic circumstances). An assemblage of BNNT mats, each the size of a small postage stamp, has been observed to provide this exceptional viscoelastic behavior at 2 K, consequently, reduce the RF power requirements, and enhance performance and significantly increase uptime of SRF systems. We can assist Jefferson Lab’s planned program to improve its C100 cryomodules to enhance CEBAF accelerator performance, and SLAC’s energy upgrade from LCLS-II to LCLS-II-HE. While the fundamental physics is identical, engineering for each design is unique to allow testing and accurate data. In Phase IIA, we propose to complete the original full C100 scope commitments with JLab, to fully prove results in real-world conditions in all eight cavities simultaneously, which will encourage commercialization into all C100s in the upgrade program and to complete the cavity demonstrations by updating the proven LCLS-II designs for cavities in LCLS-II-HE cryomodules. We have developed very recently improved processed BNNT material with enhanced vibration damping characteristics to be used for both the C100 and LCLS- II-HE cryomodules. 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 survive temperatures exceeding 1000 °C. Additionally, there is a significant industry for vibration-sensitive cryogenically-cooled test equipment.