Concept of a Staged FEL Enabled by Fast Synchrotron Radiation Cooling of   Laser-Plasma Accelerated Beam by Solenoidal Magnetic Fields in Plasma Bubble
  A novel method for generating GigaGauss solenoidal field in laser-plasma bubble, using screw-shaped laser pulses, has been recently presented in arXiv:1604.01259 [physics.plasm-ph]. Such magnetic fields enable fast synchrotron radiation cooling of the beam emittance of laser-plasma accelerated leptons. This recent finding opens a novel approach for design of laser-plasma FELs or colliders, where the acceleration stages are interleaved with laser-plasma emittance cooling stages. In this concept paper we present an outline of how a staged plasma-acceleration FEL could look like and discuss further studies needed to investigate the feasibility of the concept in detail. 
Andrei Seryi, Zsolt Lesz, Alexander Andreev and Ivan Konoplev
physics.acc-ph