Gradient Enhancement Research for Linear Accelerator Structures

For traveling wave electron linear accelerators, considerable difficulty has been encountered in demonstrating accelerating gradients in excess of 100 megavolts per meter. Attempts to operate at higher gradients suitable for future linear colliders have resulted in radio-frequency breakdown and related surface damage. In recent high-gradient accelerator tests using a resonant ring power amplifying system, an ability to minimize surface damage was demonstrated. This result was achieved by automatically responding to a breakdown event with rapid re-routing of accelerator input power and immediate restriction of energy deposition. In this project, this protection strategy will be combined with an advanced design structure to overcome the presently limited threshold of high gradient operation. In Phase I, the conceptual layout and microwave design parameters of a high power dual resonant ring system were established. During Phase II, the design and development of specialized high power components will be completed, the dual resonant ring system will be fabricated, and the overall system will be fine-tuned with a candidate high-gradient test structure embedded in the network. Resonant ring high-power tests will be conducted, and the high gradient performance of the linac structure will be evaluated and compared with that of a directly driven structure. Commercial Applications and other Benefits as described by the awardee: Success of the Phase II effort would lead to a better understanding of radio-frequency breakdown in traveling wave linear accelerators and would provide design guidance for further miniaturization of commercial accelerators for medical, radiographic, and homeland security applications.