Distributed, Multifunctional PIC Fiber-Optic Sensing System for SRF Accelerator Systems

The limit in quality factors of a superconducting radiofrequency (SRF) cavity of LCLS-II is typically due to increased RF surface resistance caused by trapped magnetic fields on the RF surface. To obtain desirable quality factor (order of 1010), the cryomodule specifications require an ambient magnetic field < 5 mG. DOE seeks radiation-resistant distributed fiber-optic sensors for measurement of residual magnetic field (RMF) magnitude at cryogenic temperatures across SRF cavities. Quench create a rapidly evaporating cryogenic fluid, leading to onset of acoustic shockwaves. Of interest are rapid detection of magnetic field and precision measurement of SRF source temperature. These sensors must be capable of operating at high pulsed magnetic fields and at a wide range of operating cryogenic temperatures. IFOS proposes a novel sensing system comprising multiplexable, multi-functional fiber-optic sensor arrays based on InP photonic integrated circuits (PIC) sensing for cryogenic temperature within the coil winding. IFOS will utilize passive magneto-optic effect in indium phosphide PIC technology and phase change in a Mach-Zehnder interferometer (MZI) for reliable, high-resolution sensing in cryomodules. IFOS will develop a polymer coated fiber coupled to InP- PIC sensor capable of high-speed multi-parameter sensing at cryogenic temperatures within the 1.0K-20K range and RMF in mG range, and other related parameters in environments required for operating superconducting RF sources. In addition to monitoring parameters like RMF and temperature, embedded optical integrated sensors in polymers can detect low-level radiation. IFOS plans to explore such a system to add radiation sensing capabilities to its distributed, multifunctional PIC-based fiber-optic sensing system. PIC-based sensing will be interrogated remotely by IFOSĺ patented high-speed interrogator. IFOS will adapt its miniature PIC interrogator based on CMOS manufacturing platform, for cryogenic applications. Additional sensing and analytics capabilities based on AI can be integrated for application to various cryomodules to resolve cross- dependencies of various parameters. In Phase I, IFOS and Fermi Lab to demonstrate the feasibility of the innovation by testing over the range of conditions expected in SRF acceleration cryomodules. Phase II will develop and test an engineering prototype system to demonstrate its full-scale multichannel (>16) capabilities for use at DOE accelerators and laboratories. Hardware ruggedness, simplicity of operation, multichannel capability, reduced SWaP-C, and robust software with built-in intelligence will be key features of the IFOSĺ photonic distributed sensor system. IFOSĺ scalable, high-speed PIC-based fiber-optic interrogator, distributed sensor offers an order-of-magnitude increase in speed, spatial and temporal resolutions over conventional electronic-based technologies. Volume cost is lower than commercial magnetometers due to the use of established PIC manufacturing in CMOS platforms.