Single Shot Characterization of High Transformer Ratio Wakefields in Nonlinear Plasma Acceleration

• Published in: Physical review letters Vol. 124; no. 4; p. 044802
• Main Authors: Roussel, R, Andonian, G, Lynn, W, Sanwalka, K, Robles, R, Hansel, C, Deng, A, Lawler, G, Rosenzweig, J B, Ha, G, Seok, J, Power, J G, Conde, M, Wisniewski, E, Doran, D S, Whiteford, C E
• Format: Journal Article
• Language: English
• Published: United States American Physical Society 31-01-2020; American Physical Society (APS)
• Subjects: Beam control; Beams (radiation); Deceleration; Emittance; Measurement methods; PARTICLE ACCELERATORS; Particle in cell technique; Plasma; Plasma acceleration; Plasma acceleration & new acceleration techniques; Single shot characterization; Transformers
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.124.044802

Plasma wakefields can enable very high accelerating gradients for frontier high energy particle accelerators, in excess of 10  GeV/m. To overcome limits on single stage acceleration, specially shaped drive beams can be used in both linear and nonlinear plasma wakefield accelerators (PWFA), to increase the transformer ratio, implying that the drive beam deceleration is minimized relative to acceleration obtained in the wake. In this Letter, 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 transformer ratios up to R=7.8. Furthermore, a spectrally based reconstruction technique, validated by 3D particle-in-cell simulations, is introduced to obtain the drive beam current profile from the decelerating wake data.