Three-dimensional analysis of wakefields generated by flat electron beams in planar dielectric-loaded structures

Abstract

An electron bunch passing through a dielectric-lined waveguide generates Č erenkov radiation that can result in a high-peak axial electric field suitable for acceleration of a subsequent bunch. Axial fields beyond gigavolt-per-meter are attainable in structures with sub-mm sizes depending on the achievement of suitable electron bunch parameters. A promising configuration consists of using a planar dielectric structure driven by flat electron bunches. In this paper we present a three-dimensional analysis of wakefields produced by flat beams in planar dielectric structures thereby extending the work of Tremaine, Rosenzweig, and Schoessow, Phys. Rev. E 56, 7204 (1997)] on the topic. We especially provide closed-form expressions for the normal frequencies and field amplitudes of the excited modes and benchmark these analytical results with finite-difference time-domain particle-in-cell numerical simulations. Finally, we implement a semianalytical algorithm into a popular particle-tracking program thereby enabling start-to-end high-fidelity modeling of linear accelerators based on dielectric-lined planar waveguides.

Simulation studies for dielectric wakefield programme at CLARA facility

“…Two codes were used for simulation studies: the space charge tracking code Impact-T [24] and the particle-in-cell (PIC) code VSim [25]. Impact-T uses an electrostatic PIC model for bunch space charge and analytical mode decomposition method to calculate the DLW wakefield [20]. This approach offers a significant reduction in simulation time compared to fully electromagnetic PIC methods and is especially useful for structures that are transversely large relative to the driving bunch, for example a dechirper with large aperture or a wide waveguide with a flat beam for DWA.…”

“…The lowest order LSM 11 mode has a longitudinal electric field component, making this the fundamental mode for acceleration of a witness bunch in a DWA. It should be noted that this mode, shifted by π/2 in phase, has an electric quadrupole component; this is a result of the boundary conditions and occurs without a drive beam offset [20]. Therefore transverse wakefields are always excited in a rectangular DLW.…”

“…A natural choice for that initial programme is a planar structure with variable gap. For given structure dimensions it is possible to calculate the frequencies of longitudinal section magnetic (LSM) and longitudinal section electric (LSE) modes that have phase velocity v p = c [19,20]. These are the wakefield modes and are analogous to the transverse electric and magnetic modes seen in all metal waveguides.…”

Impedances of anisotropic round and rectangular chambers

“…There are many papers which describe impedance calculations of steady-state impedance for isotropic round and flat layered chambers [5][6][7][8][9][10] with translational symmetry in the beam direction. The solutions for isotropic structures are obtained in analytical form or a field-matching approach can be used to reduce the problem to a simple matrix equation.…”

Tunable Plasma-Based Energy Dechirper

“…Removal of energy chirps using corrugated pipes [13] and dielectric-based slab structures [14] has been experimentally demonstrated. To date, these structures have been shown to remove chirps on the sub-MeV/mm level, with current theoretical estimates indicating potential for growth [15][16][17]. To compensate the extreme energy chirps generated in plasma-based accelerators within distances comparable or shorter than the accelerator size, a technique capable of removing chirps far exceeding those experimentally demonstrated is required.…”