Efficiency versus instability in plasma accelerators

TL;DR

This paper establishes a fundamental relation between efficiency and instability in plasma wake-field accelerators, highlighting the trade-offs and limitations for future high-energy collider applications.

Contribution

It derives a universal efficiency-instability relation for plasma accelerators in the blowout regime and discusses methods to suppress instability, revealing fundamental efficiency limits.

Findings

Efficiency-instability relation constrains accelerator performance.

Suppression of instability via BNS damping requires high energy variation.

High efficiency regimes face fundamental instability limitations.

Abstract

Plasma wake-field acceleration is one of the main technologies being developed for future high-energy colliders. Potentially, it can create a cost-effective path to the highest possible energies for e+e- or {\gamma}-{\gamma} colliders and produce a profound effect on the developments for high-energy physics. Acceleration in a blowout regime, where all plasma electrons are swept away from the axis, is presently considered to be the primary choice for beam acceleration. In this paper, we derive a universal efficiency-instability relation, between the power efficiency and the key instability parameter of the trailing bunch for beam acceleration in the blowout regime. We also show that the suppression of instability in the trailing bunch can be achieved through BNS damping by the introduction of a beam energy variation along the bunch. Unfortunately, in the high efficiency regime, the required energy variation is quite high, and is not presently compatible with collider-quality beams. We would like to stress that the development of the instability imposes a fundamental limitation on the acceleration efficiency, and it is unclear how it could be overcome for high-luminosity linear colliders. With minor modifications, the considered limitation on the power efficiency is applicable to other types of acceleration.