Aluminum Nitride Radio Frequency Windows

72560S03-I New window materials that can handle multi-megawatt radio frequency (RF) powers are needed to increase the reliability of RF windows for linear particle accelerators. Aluminum nitride would be an excellent window material due to its high thermal conductivity, high dielectric strength, low secondary electron emission, and high mechanical strength if its dielectric loss (loss tangent) could be controlled/reduced. This project will reduce the dielectric loss of aluminum nitride, without degrading its thermal, mechanical, and other dielectric properties, by controlling its microstructure through processing steps. The new AlN dielectric will enable window designers to increase the amount of the power that can be coupled into accelerators. Phase I will develop a novel method for uniformly distributing a sintering aid, which will eliminate the porosity and grain growth during sintering. The microwave dielectric properties will be measured and correlated with the sintered microstructures. Commercial Applications and Other Benefits as described by awardee: Almost every medium-to-high vacuum electron device should benefit from the new non-toxic, vacuum compatible, low loss, high thermal conductivity aluminum nitride. Applications include klystrons and gyrotrons that supply microwave energy for improving chemical processes and materials processing; klystrons for direct broadcast satellites; gyrotrons for magnetic fusion based on electron cyclotron heating; and microwave communications.