Corrosion is a serious issue in copper cooling systems, particularly when high purity coolant is not available. This a serious issue for marine systems subject to saltwater contamination. With U.S. Navy funding, CCR and N.C. State University developed a system that applies a nano-scale ceramic coating to cooling surfaces to separate the copper from the coolant without impacting heat transfer. A system using Atomic Layer Deposition demonstrated that coolant system lifetimes could be increased by more than 300%. The Navy is currently qualifying the system for critical defense systems.

Magnetrons are perhaps the lowest cost, most efficient source of RF power. These devices, however, are oscillators, so there is no control of the phase, frequency, and amplitude. This prevents use for many applications, including accelerators, radar, and communications systems. CCR is working with SLAC National Accelerator Laboratory to address this issue. In 2019, CCR, in collaboration with Fermilab, successfully tested a 10 kW, 1.3 GHz magnetron system for driving superconducting accelerators. The current program is developing a simpler and more compact system using varactor diodes.

Klystrons are the RF source of choice for many systems, including radar, communications, and accelerators. The klystron is a well established RF source but lacks the efficiency required for many applications. Typical efficiencies range from 55 – 65%. CCR is building a 100 kW CW, 1.3 GHz klystron designed to operate at 80% efficiency. The RF circuit uses the core oscillation method (COM) to more effectively bunch the electron beam for RF power extraction. A prototype klystron is under construction.

Multipactor emission is a serious problem for vacuum windows transmitting MW levels of RF power. Multipactor results when high RF fields cause electron emission avalanche on the material surface. This is mitigated by a 10-15 Angstrom metal alloy coating to reduce secondary electron emission and dissipate electric charge. This coating is typically applied using hot wire sputtering, which works well for small structures, but is insufficient for larger ones. CCR is teamed with VaporPulse, Inc. and Ultramet to develop coating processes using Atomic Layer Deposition and/or Chemical Vapor Deposition. These new process will improve performance and treat structures up to 24 inches or more.

Inductive output tubes (IOTs) are highly efficient sources of RF power from a few hundred MHz up to 1.2 GHz. Efficiencies exceeding 80% are easily achieved, making them desirable for many applications where cost is important. Single beam IOTs, however, are limited to power level typically less than 30 kW. A number of important applications, such as waste treatment and water purification, required 200 kW or more of continuous power. CCR is developing a 700 MHz multiple beam IOT designed to produce 200 kW CW with an efficiency exceeding 80%. A prototype is scheduled for testing in spring 2022.