Recently
we showed that ideal waterbag electron bunches ? uniformly filled, hard-edged
ellipsoids of charge - can be realized in practice. The linear self-fields
of such objects enable thermal-emittance-limited beams and very efficient
compression. We now propose to extract the electrons from an ultra-cold
plasma, created by photo-ionization of a cloud of laser-cooled atoms,
thus lowering the thermal emittance to below 0.1 micron. In addition,
pulsed extraction leads to fs bunch lengths, without the use of ultra-fast
lasers or magnetic compression. We will present GPT simulations of the
production of ultra-cold, ultra-short waterbags in realistic settings,
showing that orders of magnitude in beam brightness may be gained. Experiments
are underway, whose status will be reported.