A photon–photon collider based on synchrotron <i>γ</i> rays in hollow plasma channels

We propose a photon–photon collider based on synchrotron gamma sources driven by relativistic electron beams in hollow plasma channels. The collimated (with a divergence angle of ∼1 mrad) and ultrabrilliant (&amp;gt;1028 photons s−1⋅mrad−2⋅mm−2 per 0.1% bandwidth at 0.6 MeV) photon beams are generated by strong electromagnetic fields induced by current filamentation instability, and up to ∼106 Breit–Wheeler (BW) pairs can be created per shot. Notably, the usage of hollow plasma channels not only enhances synchrotron radiation, but also allows flexible control of the produced photon beams, ensuring the alignment of the two colliding beams and maximizing the two-photon BW process. This setup has the advantage of a clean background by eliminating the yield from the nonlinear BW process, and the signal-to-noise ratio is higher than 102.