# Generation of a wakefield undulator in plasma with transverse density gradient

## TL;DR

This paper demonstrates that a plasma with a transverse density gradient can generate a wakefield acting as a high-strength, short-period undulator, potentially enabling compact plasma-based free electron lasers.

## Contribution

It introduces a novel method to produce a plasma undulator using a transverse density gradient, combining wakefield acceleration and undulation in a unified plasma device.

## Key findings

- A density gradient creates a transverse wakefield force on a witness bunch.
- Oscillating density gradients can produce a periodically varying force, functioning as an undulator.
- Estimated magnetic field strength exceeds ten Tesla.

## Abstract

We show that a short relativistic electron beam propagating in a plasma with a density gradient perpendicular to the direction of motion generates a wakefield in which a witness bunch experiences a transverse force. A density gradient oscillating along the beam path would create a periodically varying force---an undulator, with an estimated strength of the equivalent magnetic field more than ten Tesla. This opens an avenue for creation of a high-strength, short-period undulators, which eventually may lead to all-plasma, free electron lasers where a plasma wakefield acceleration is naturally combined with a plasma undulator in a unifying, compact setup.