SBIR-STTR Award

Dielectric based accelerators have potentials to provide a low cost, ultra-high gradient, high energy collider design, but, due to the available rf power limitations in the available test facilities and some design issues in the past, they have not yet been tested to date under high gradient conditions. We will develop and conduct high gradient rf tests of a Standing Wave (SW) Dielectric Loaded Accelerating (DLA) structure, which allows high gradient ( & gt 100 MV/m) tests with a usage of & lt;10 MW input rf power. The structure is planned to be tested at the Naval Research Laboratory, where it can be operated at gradients as high as 170 MV/m with 20 MW rf power from the X-band Magnicon. In Phase I of this project, an X-band standing wave DLA structure will be designed, fabricated, and bench tested in preparation for a high power rf test at NRL. Commercial Applications and Other

Benefits:
This rf breakdown study using a standing wave DLA structure will very likely lead to demonstration of an accelerating gradient as high as 170 MV/m which may lead toward the design of a future high energy collider. Alternatively, this experiment could provide the first hard evidence of rf breakdown limits of dielectric based accelerators which provides useful experimental data for the global effort to understand the breakdown mechanism

One of the most attractive features of dielectric based accelerators are their potential capability of operating at ultra-high gradients, which is highly desirable for future high energy collider designs, as well as for industrial and medical accelerator applications. This prediction of ultra-high gradients is widely accepted but has never been verified because of experimental difficulties. We propose to develop an X-band standing wave DLA structure to allow high gradient ( & gt; 100 MV/m) tests with a usage of & lt;10 MW input rf power. The new design couples the rf on the axis of the structure with a matching cell capable of post fabrication tuning. The new design also allow use of a standard SLAC type X-band TM01 mode launcher as an rf feed, which will eliminate any uncertainty in terms of rf breakdown in the coupler below 20 MW. This new design will provide a good opportunity to achieve the goal of verifying high field breakdown limits in dielectric structures. Under Phase I of the project, we have not only successfully completed all objectives listed in the Phase I proposal but also performed a portion of a task originally allotted to Phase II. We developed a SW DLA structure and performed a high power rf test during the period of Phase I. Two issues arose in the Phase I high power rf test: detuning by multipactor and arcing at the copper end plug. The experimental results were thoroughly analyzed. A simple circuit model is introduced to represent the multipactor effect in a SW DLA structure and good agreement is reached with the experimental data. Meanwhile, in order to address these two issues and achieve the ultimate goal of the project ( & gt;100 MV/m gradient), we have modified the engineering design of the structure and experimental plan for Phase II. A new SW DLA structure will be fabricated in Phase II of the project with solutions to the issues found in Phase I incorporated. Two more high power rf tests will be performed at NRL in Phase II to achieve the ultimate goal of the project. Commercial Applications and Other

Benefits:
This rf breakdown study using a standing wave DLA structure will very likely lead to the observation of gradients as high as 170 MV/m or the first direct measurements of rf breakdown limits in dielectric based accelerators. This project will also provide useful experimental data for the global effort to understand the rf breakdown mechanism in general and may lead to the design of a future collider based on dielectric device technology.