Staging of high-gradient wakefield accelerators

Accelerating particles to high energies with a high-gradient wakefield accel- erator may require use of multiple stages. Coupling beams from one stage to another can be difficult due to high divergence and non-negligible energy spreads. We review the challenges, technical requirements and currently pro- posed methods for solving the staging problem

Staging of plasma-wakefield accelerators

Accelerating particles to high energies with a high-gradient wakefield accel-erator may require use of multiple stages. Coupling beams from one stageto another can be difficult due to high divergence and non-negligible energyspreads. We review the challenges, technical requirements and currently pro-posed methods for solving the staging proble

Self-correcting longitudinal phase space in a multistage plasma accelerator

Plasma accelerators driven by intense laser or particle beams provide gigavolt-per-meter accelerating fields, promising to drastically shrink particle accelerators for high-energy physics and photon science. Applications such as linear colliders and free-electron lasers (FELs) require high energy and energy efficiency, but also high stability and beam quality. The latter includes low energy spread, which can be achieved by precise beam loading of the plasma wakefield using longitudinally shaped bunches, resulting in efficient and uniform acceleration. However, the plasma wavelength, which sets the scale for the region of very large accelerating fields to be 100 µm or smaller, requires bunches to be synchronized and shaped with extreme temporal precision, typically on the femtosecond scale. Here, a self-correction mechanism is introduced, greatly reducing the susceptibility to jitter. Using multiple accelerating stages, each with a small bunch compression between them, almost any initial bunch, regardless of current profile or injection phase, will self-correct into the current profile that flattens the wakefield, damping the relative energy spread and any energy offsets. As a consequence, staging can be used not only to reach high energies, but also to produce the exquisite beam quality and stability required for a variety of applications

High-quality Beams from a High-efficiency Plasma Accelerator at DESY’s FLASHForward Facility, and beyond

Plasma accelerators can drastically shrink large-scale future accelerator facilities such as a linear collider. Maintaining high beam quality and accelerating with high energy efficiency is key to delivering high luminosity per wall-plug power. However, this is particularly challenging in a plasma accelerator due to their microscopic size—extreme precision and stability is required. We present recent results from DESY’s FLASHForward plasma-accelerator facility, showing preserved energy spread and charge while accelerating with GV/m gradients at record efficiency and stability. Moreover, a new concept for self-correcting plasma acceleration is presented, which may provide orders of magnitude better beam quality and stability for applications in the future

Emittance Preservation in Advanced Accelerators

Emittance is a beam quality that is vital for many future applications of advanced accelerators, such as compact free-electron lasers and linear colliders. In this paper, we review the challenges of preserving the transverse emittance during acceleration, both inside and outside accelerator stages. Sources of emittance growth range from space charge and instabilities caused by transverse wakefields, which can occur in any advanced accelerator scheme regardless of medium or driver type, to sources more specific to plasma accelerators, such as mismatching, misalignment, ion motion, Coulomb scattering, chromaticity between stages, and more

Status of and upgrade concepts for HALHF: the hybrid, asymmetric, linear Higgs factory

This contribution outlines the HALHF concept, which combines the high gradients achievable in plasma-wakefield acceleration with conventional radio-frequency acceleration. In HALHF, beam-driven plasma-wakefield cells are used to accelerate electrons to high energy. Because plasma-based acceleration of positrons is problematic, conventional RF acceleration is used but to much lower energy. The HALHF concept utilises not only asymmetric energies but also asymmetric bunch charges and asymmetric transverse emittances, leading to comparable luminosity to conventional facilities but much lower capital cost. Possible upgrades to the HALHF facility are discussed, in particular to the $t\bar{t}$ threshold and to 550 GeV, where the Higgs self-coupling and $t\bar{t}H$ coupling can be measured. Other upgrades include the provision of two interaction points, to implement a $γ–γ$ collider of two possible types and finally a symmetric high-energy collider if the problem of plasma-based positron acceleration can be solved

Signal subtraction of consecutive electron bunches from a high-repetition-rate plasma-wakefield accelerator

Beam-driven plasma-wakefield acceleration is a promising avenue for the future design of compact linear accelerators with applications in high-energy physics and photon science. In order to meet the luminosity and brilliance demands of current users, at least thousands of bunches must be delivered per second – many orders of magnitude beyond the current state-of-the-art of plasma-wakefield accelerators, which typically operate at the Hz-level. As recently explored at FLASHForward, the fundamental limitation for the highest repetition rate is the long-term motion of ions that follows the dissipation of the driven wakefield (R. D’Arcy, et al. Nature 603, 58–62 (2022)). The recovery of the plasma is observed in the images of probe bunches, separated from a preceding bunch in increments of 0.77 ns. The properties of the electron bunches are imaged using scintillator screens, the light-output of which lasts for milliseconds. As all bunches arrive well within the scintillation lifetime of the screen of 380 µs, an image processing technique capable of resolving individual bunches is needed. Here we present a technique which uses many shots of the preceding bunch to accurately identify and remove its signal from the overlapped signal of the subsequent bunch pair. With this method the effects of the perturbed plasma on the subsequent bunch pair can be observed with high temporal resolution, and thus the effects of the long-term ion motion on the probe bunches can be observed. This allows high-repetition-rate processes to be studied in greater detail – an essential first step in advancing beam-driven plasma-wakefield acceleration to a level required for meaningful application to high-energy-physics and photon-science facilities of the future

Signal Subtraction of Consecutive Electron Bunches from a High-Repetition-Rate Plasma-Wakefield

Plasma-wakefield acceleration (PWFA) is one of the main candidates for future compact-accelerator technologies with applications in high energy physics and photon science. For PWFA, which currently operates at Hz level, to meet the luminosity and brilliance demands of current users, at least thousands of bunches must be delivered per second. As recently explored at FLASHForward, DESY, the fundamental limitation for the highest repetition rate is the long-term motion of ions that follows the dissipation of the driven wakefield (D’Arcy, R. et al. Recovery time of a plasma-wakefield accelerator. Nature (accepted) (2021)). The recovery of the plasma to an undisturbed state after the driving of a wakefield was observed in the images of consecutive electron bunches, separated by tens of nanoseconds, while the imaging screens have scintillation lifetimes of the order milliseconds. As such, an image processing technique capable of resolving individual bunches within that lifetime is needed. This technique - termed the ’subtraction method’ - uses many shots of a preceding bunch to accurately identify and remove its signal from the overlapping signal of a subsequent bunch. As a result, high-repetition-rate processes can be studied to advance PWFA for meaningful application to facilities of the future