Publication Date

2025

Document Type

Dissertation/Thesis

First Advisor

Lu, Xueying

Degree Name

Ph.D. (Doctor of Philosophy)

Legacy Department

Department of Physics

Abstract

Future accelerator facilities are increasingly constrained by the cost and footprint of conventional radiofrequency technology. Advancing both accelerating gradient and beam-to-wake energy transfer efficiency in the sub-terahertz (sub-THz) regime offers a credible path toward compact machines. Short wavelengths strengthen beam–structure coupling and enable small-aperture, high-impedance geometries; paired with tailored drive-beam current profiles, they can simultaneously raise gradient and transformer ratio.

This dissertation reports the design, fabrication, and beam testing of a sub-THz structure-wakefield accelerating (SWFA) device evaluated at the Argonne Wakefield Accelerator (AWA). The emittance-exchange (EEX) beamline was used to generate prescribed longitudinal current profiles in two modes: (i) a single short drive bunch to benchmark achievable fields, and (ii) a two-bunch configuration employing a triangularly shaped drive followed by a long witness to sample the accelerating wake and determine the transformer ratio. Structure design was guided by analytical wake models and time-domain simulations; room-temperature cold measurements provided fabrication verification prior to beam operation.

Experimentally, we obtained a decelerating gradient of about 50 MV/m using an average drive-bunch charge of 6.4 nC with rms bunch length 0.28 mm. With a 2.5 nC triangular drive bunch, we measured an average transformer ratio of approximately 3. The trends and magnitudes agree with model predictions within estimated systematic uncertainties dominated by charge calibration and bunch-length reconstruction. These measurements demonstrate that sub-THz SWFA with shaped beams can deliver simultaneously high gradient and high beam-to-wake efficiency.

The results motivate next steps that target increased transformer ratio and net witness energy gain through improved current-profile fidelity, multi-structure staging, and refined structure impedance. Collectively, the demonstrated performance establishes sub-THz SWFA as a viable building block for high-gradient, high-efficiency acceleration and informs the design space for next-generation compact linear accelerators serving both fundamental science and applied photon-science users.

Extent

154 pages

Language

en

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

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Text

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