MIT/PSFC, Cambridge, Massachusetts, USA
ANL, Lemont, Illinois, USA
Euclid TechLabs, Solon, Ohio, USA
Northern Illinois University, DeKalb, Illinois, USA
We present our recent results generating 510 MW of power at 11.7 GHz using a metamaterial-based metallic power-extractor for application in structure-based wakefield acceleration (SWFA). SWFA is a novel acceleration scheme in which high-charge electron bunches are passed through a power extractor structure to produce a high-intensity wakefield. This wakefield can then be used to accelerate a witness bunch in the same beamline or passed to a separate acceleration beamline. MIT’s approach uses a specialized metamaterial for the power extractor design. By using a metamaterial, we can overcome some of the challenges faced by other SWFA techniques. Here, we discuss the Stage 3 experiment. The Stage 1 and Stage 2 experiments successfully demonstrated the functionality of the metamaterial approach by generating high power RF pulses using the 65 MeV electron beam at the Argonne Wakefield Accelerator (AWA) facility. The 510 MW result from Stage 3 experiment is the highest power generated to-date for SWFA at AWA, and was enable by significant design improvements, including an all-copper structure, fully-symmetric coupler design, and breakdown risk-reduction treatment.
Euclid Beamlabs, Bolingbrook, USA
ANL, Lemont, Illinois, USA
TUB, Beijing, People’s Republic of China
Illinois Institute of Technology, Chicago, Illinois, USA
Euclid TechLabs, Solon, Ohio, USA
As part of the Argonne 500 MeV short pulse Two Beam Wakefield Acceleration Demonstrator, a single cell X-band dielectric disk loaded accelerator (DDA) has been designed, fabricated, and tested at high power at the Argonne Wakefield Accelerator. The DDA should provide a short pulse (~20 ns) high gradient (>300 MV/m) accelerator while maintaining a reasonable r/Q and high group velocity. This will allow a significantly larger RF-to-beam efficiency than is currently possible for conventional accelerating structures. A low loss barium titantate ceramic, µr = 50, was selected, and a low temperature brazing alloy chosen to preserve the dielectric properties of the ceramic during brazing. High power testing produced breakdown at the triple junction, resulting from the braze joint design. No evidence of breakdown was observed on the iris of the disk, indicating that the maximum surface electric field on the dielectric was not reached. An improved braze joint has been designed and is in production, with high power testing to follow.
TUXB06
Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA
UCLA, Los Angeles, USA
Northern Illinois University, DeKalb, Illinois, USA
ANL, Lemont, Illinois, USA
To overcome limits on total acceleration achievable in plasma wakefield accelerators, specially shaped drive beams can be used to increase the transformer ratio, implying that the drive beam deceleration is minimized in comparison with acceleration obtained in the wake. We report the results of a nonlinear PWFA, high transformer ratio experiment using high-charge, longitudinally asymmetric drive beams in a plasma cell. An emittance exchange process is used to generate variable drive current profiles, in conjunction with a long (multiple plasma wavelength) witness beam. The witness beam is energy-modulated by the wakefield, yielding a response that contains detailed spectral information in a single-shot measurement. Using these methods, we generate a variety of beam profiles and characterize the wakefields, directly observing beam-loaded transformer ratios up to 7.8. Further, a spectrally-based current reconstruction technique, validated by 3D particle-in-cell simulations, is introduced to obtain the drive beam profile from the decelerating wakefield data.