Development of Wakefield Accelerating Structures at Ultra-high Frequencies

The development of a multi-TeV e+e- linear collider is a key priority set by the P5 panel, which established the long-term strategy of the U.S. HEP program. A Two-Beam Acceleration (TBA) is one of the most promising approaches for this facility due to its potential for achieving high efficiency and the ability to accelerate particles with positive and negative charges. However, there are still challenges to develop high-gradient structures above 100 GHz and rf components with sufficient precision to implement structure wakefield acceleration in the short-pulse TBA approach. In response to this problem, RadiaBeam in collaboration with the Argonne Wakefield Accelerator (AWA) Facility proposes will build upon our recent experiences on diagnostics for 110 GHz structures and fabrication studies for a collinear wakefield accelerating structure at 200 GHz. We will develop and build the enabling rf components and instrumentation at ~180 GHz in the context of developing practical TBA SWFA structures: rf couplers with broad bandwidth; efficient waveguide coupling between the decelerator and the accelerator with low rf loss; multipactor-free rf pickup/directional couplers; phase/power shifters; and rf loads. In Phase I we will perform the RF design the 180 GHz structure for the TBA, and the aforementioned RF components. This will be followed by conceptual engineering design, including thermal and mechanical considerations. We will also fabricate and characterize a single cell structure to establish that we can achieve the surface finish and dimensional tolerances required for a GHz structure. The developed accelerating structure will be used in the future electron-positron collider. Other commercial applications include compact Free-Electron Lasers, Terahertz sources and emerging Inverse Compton Sources. Compact high-gradient accelerators are also required for numerous industrial, medical and military applications.