RESUMO
The FLASHForward experimental facility is a high-performance test-bed for precision plasma wakefield research, aiming to accelerate high-quality electron beams to GeV-levels in a few centimetres of ionized gas. The plasma is created by ionizing gas in a gas cell either by a high-voltage discharge or a high-intensity laser pulse. The electrons to be accelerated will either be injected internally from the plasma background or externally from the FLASH superconducting RF front end. In both cases, the wakefield will be driven by electron beams provided by the FLASH gun and linac modules operating with a 10 Hz macro-pulse structure, generating 1.25 GeV, 1 nC electron bunches at up to 3 MHz micro-pulse repetition rates. At full capacity, this FLASH bunch-train structure corresponds to 30 kW of average power, orders of magnitude higher than drivers available to other state-of-the-art LWFA and PWFA experiments. This high-power functionality means FLASHForward is the only plasma wakefield facility in the world with the immediate capability to develop, explore and benchmark high-average-power plasma wakefield research essential for next-generation facilities. The operational parameters and technical highlights of the experiment are discussed, as well as the scientific goals and high-average-power outlook. This article is part of the Theo Murphy meeting issue 'Directions in particle beam-driven plasma wakefield acceleration'.
RESUMO
A tunable plasma-based energy dechirper has been developed at FLASHForward to remove the correlated energy spread of a 681 MeV electron bunch. Through the interaction of the bunch with wakefields excited in plasma the projected energy spread was reduced from a FWHM of 1.31% to 0.33% without reducing the stability of the incoming beam. The experimental results for variable plasma density are in good agreement with analytic predictions and three-dimensional simulations. The proof-of-principle dechirping strength of 1.8 GeV/mm/m significantly exceeds those demonstrated for competing state-of-the-art techniques and may be key to future plasma wakefield-based free-electron lasers and high energy physics facilities, where large intrinsic chirps need to be removed.
RESUMO
The hose instability of the drive beam constitutes a major challenge for the stable operation of plasma-wakefield accelerators. In this Letter, we show that drive beams with a transverse size comparable to the plasma blowout radius generate a wake with a varying focusing along the beam, which leads to a rapid detuning of the slice-betatron oscillations and suppresses the instability. This intrinsic stabilization principle provides an applicable and effective method for the suppression of the hosing of the drive beam and allows for a stable acceleration process.
RESUMO
Mitigation of the beam hose instability in plasma-based accelerators is required for the realization of many applications, including plasma-based colliders. The hose instability is analyzed in the blowout regime including plasma ion motion, and ion motion is shown to suppress the hose instability by inducing a head-to-tail variation in the focusing force experienced by the beam. Hence, stable acceleration in plasma-based accelerators is possible, while, by use of proper bunch shaping, minimizing the energy spread and preserving the transverse beam emittance.
RESUMO
Current models predict the hose instability to crucially limit the applicability of plasma-wakefield accelerators. By developing an analytical model which incorporates the evolution of the hose instability over long propagation distances, this work demonstrates that the inherent drive-beam energy loss, along with an initial beam-energy spread, detunes the betatron oscillations of beam electrons and thereby mitigates the instability. It is also shown that tapered plasma profiles can strongly reduce initial hosing seeds. Hence, we demonstrate that the propagation of a drive beam can be stabilized over long propagation distances, paving the way for the acceleration of high-quality electron beams in plasma-wakefield accelerators. We find excellent agreement between our models and particle-in-cell simulations.
