Development and high-power testing of an X -band dielectric-loaded power extractor

Abstract

Dielectric loaded structures are promising candidates for use in the structure wakefield acceleration (SWFA) technique, for both the collinear wakefield and the two-beam acceleration (CWA and TBA respectively) approaches, due to their low fabrication cost, low rf losses, and the potential to withstand high gradient. A short pulse (≤20 ns) TBA program is under development at the Argonne Wakefield Accelerator (AWA) facility where dielectric loaded structures are being used for both the power extractor/transfer structure (PETS) and the accelerator. In this study, an X-band 11.7 GHz dielectric PETS was developed and tested at the AWA facility to demonstrate high power wakefield generation. The PETS was driven by a train of eight electron bunches separated by 769.2 ps (9 times of the X-band rf period) in order to achieve coherent wakefield superposition. A total train charge of 360 nC was passed through the PETS structure to generate ∼200 MW, ∼3 ns flat-top rf pulses without rf breakdown. A future experiment is being planned to increase the generated rf power to approximately ∼1 GW by optimizing the structure design and improving the drive beam quality.

Schemes for Acceleration a Part of Electrons of Drive Electron Bunches in the Dielectric Wakefield Structure

“…For the electron energy of the beam of 4.5 MeV [14] the resonance frequency of E 01 mode of a wake wave equal to 8.415 GHz. The wavelength of the wake wave in the waveguide is 3.…”

Roadmap for Structure-based Wakefield Accelerator (SWFA) R&D and its challenges in beam dynamics

“…up to a plateau, the bunches in a train will experience increased energy reduction from the deceleration field built up by the previous bunches until the plateau is reached [38]. In the short-pulse TBA concept, in order to achieve a high efficiency, a bunch train needs to pass through multiple PETS sections until nearly 90% of the beam energy is extracted.…”

“…As a result, the design of the beam focusing optics on the PETS beamline is very challenging. The quad and BPM system used in the CLIC design provides one possible solution [38]. However, the drive beam configuration in the short-pulse TBA is significantly different from the CLIC drive beam.…”

“…In the TBA approach, although the structures operate in the microwave regime, the acceleration gradient may be significantly enhanced due to the use of short RF pulses (∼ 10 ns) from the wakefield power extractors. With improved high-charge drive beam generation, in 2020, a 200-MW, 5-ns wakefield pulse out of a dielectric structure [38] and 380 MW (later 510 MW) out of a novel metamaterial structure [18,68] were reported. As a result, over 350 MV/m of gradient was demonstrated in short X-band structures [19].…”

Fully 3D time-dependent simulation of free electron laser within an overmoded rectangular waveguide

“…We can obtain the time structure and power spectrum in the fundamental mode of the output pulses at the undulator exit as shown in figure 4. The longitudinal behavior of the radiated process can be understood as a superradiant emission [29]. For simplicity, we assume that all the electron bunches in the bunch-train have the same distributions with uniform space equal to the radiation wavelength λ and the distribution variations are negligible during their passages along the whole undulator length.…”