Researchers hit milestone in accelerating particles with plasma (SLAC press release)Future plasma wakefield accelerators with the same final energy may be up to 500 times smaller than the existing accelerators. What's the catch?
High-efficiency acceleration of an electron beam in a plasma wakefield accelerator (Litos et al., Nature)
The bunches of electrons are accelerated by some waves in plasma. We need many electrons to get a lot of energy; with a great efficiency; to achieve a uniform energy and move in the same direction etc.
So far, the experiments would heavily fail at least in one of the criteria. But the newest experiment managed to achieve all of the virtues, roughly speaking.
To make the progress even more applicable as a replacement of LHC-like accelerators, one needs even more constant energy etc. See the articles above for details.