The issue with charged particle beams is the charged particles are mutually repulsive, so the beam expands rapidly once out of the confining magnets or electrostatic fields used to drive and aim it. In space, the usual counter is to have another charge particle beam of the opposite charge fired along the same beam path to make a neutral ion beam (in which case the issue of beam expansion is the neutral particles are "hot" and the beam thermally expands).
In the atmosphere, particle beam weapons also have the issue of ramming into the molecules of the atmosphere, scattering the beam even further and soaking up much of the available energy. Back in the 1980's, it was thought that the best way to counter this would be to fire a high powered laser and then fire the charged particle beam (usually charged electrons) into the channel created by the laser. The high energy of the laser would essentially "push" the air molecules out of the way by violently heating them and the charged particle beam would run through the partial vacuum created by the laser.
"Why not just shoot down the target with the laser?" you might ask. The state of the art was still rather primitive, so lasers of sufficient power to actually shoot down missiles or aircraft were not common at all (consider that the USN and USAF are considering arming ships and airplanes with 100kW laser weapons starting in 2018 to see how difficult this really is), and charged particle beams have kill mechanisms which were considered different and difficult enough to counter with any reasonable technology of the day. Atomic Rockets has a good section on "conventional space weapons like lasers and particle beams here.
So particle beam weapons can either be fired in pairs (proton or positively charged ions with electron beams) to create neutral particle beams, which are thermally limited for range (a few hundred to a few thousand kilometres) or in the atmosphere can be fired down a near vacuum channel created by firing a laser pulse first.
As for "portability", realistic limitations on energy conversion, heat reject and the beam making machinery suggest that you are talking about large AFV's, ships and really large (ISS sized) spacecraft using plausible near term technology.