  It is widely accepted that the next lepton collider beyond a Higgs factory
would require center-of-mass energy of the order of up to 15 TeV. Since, given
reasonable space and cost restrictions, conventional accelerator technology
reaches its limits near this energy, high-gradient advanced acceleration
concepts are attractive. Advanced and novel accelerators (ANAs) are leading
candidates due to their ability to produce acceleration gradients on the order
of 1--100~GV/m, leading to compact acceleration structures. Over the last 10-15
years significant progress has been achieved in accelerating electron beams by
ANAs. For example, the demonstration of several-GeV electron beams from
laser-powered capillary discharge waveguides, as well as the proof-of-principle
coupling of two accelerating structures powered by different laser pulses, has
increased interest in ANAs as a viable technology to be considered for a
compact, TeV-class, lepton linear collider.
  However, intermediate facilities are required to test the technology and
demonstrate key subsystems. A 20-100 GeV center-of-mass energy ANA-based lepton
collider can be a possible candidate for an intermediate facility. Apart from
being a test beam facility for accelerator and detector studies, this collider
will provide opportunities to study muon and proton beam acceleration,
investigate charged particle interactions with extreme electromagnetic fields
(relevant for beam delivery system designs and to study the physics at the
interaction point), as well as precision Quantum Chromodynamics and Beyond the
Standard Model physics measurements. Possible applications of this collider
include the studies of $\gamma\gamma$ and $e$-ion collider designs.
