Meet Mr Fusion
Chip-scale integration offers precise, micro actuators and high electric field generation at modest power levels that will enable several order of magnitude decreases in the volume needed to accelerate the ions. Furthermore, thermal isolation techniques will enable high efficiency beam to power converters, perhaps making chipscale self-sustained fusion possible.
Or so the project was described in 2009's budget. So why was the project dropped? Guesses as follows:
(1) The project failed. (DARPA hasn't actually said this, however.)
(2) The project was a success, and now it's gone commercial.
(3) The project was a success, and now it's classified.
Personally I'm looking forward to my fusion-powered laptop and my fusion-powered phone, which can be turned into nuclear grenades in the event of a terrorist attack.