Gradient Enhancement Research for Linear Accelerator Structures

Conventional linear accelerator systems that operate with RF pulse lengths in the range of 150 to 400 nanoseconds, at both 11.4 and 17.1 gigahertz, have been unable to operate on a reliable long term basis with gradients greater than 70 to 75 megavolts per meter. Attempts to operate at the higher gradients needed for future linear colliders have resulted in RF-breakdown-related surface damage and loss of circuit phase integrity. Recent high gradient accelerator tests using a resonant ring power source have demonstrated an ability to minimize surface damage, by rapidly rerouting the power flow and truncating energy deposition during an RF breakdown in the linac structure. This inherent protection feature, combined with structure configuration improvements, has the potential for elevating the presently limited threshold for high gradient operation. This project will develop a linear accelerator test module to evaluate the high gradient performance of two identical, advanced-design traveling wave structures: one driven directly from a high power klystron source and the other embedded in a power-amplifying resonant ring system. Phase I will establish the microwave design parameters and the system layouts required to perform the proposed high gradient tests. Commercial Applications and other Benefits as described by the awardee: A linear accelerator test module with high-gradient performance would lead to a better understanding of the field gradient limitations of traveling wave linear accelerators and provide design guidance for the ongoing miniaturization of commercial accelerators for medical, industrial, and homeland security applications.