Antiproton beam

An antiproton beam was a confined beam of antiprotons.

Encountered in 2267, the "planet killer" used a beam of "pure" antiprotons (an incredible scientific concept, at the time) as its primary weapon, capable of destroying whole planets. 

When she was undercover with the Maquis, Seska developed a tactic by which she disabled the computer core of a Cardassian frigate above Bajor with a modified antiproton beam that penetrated its shields and hull. In 2372, Chakotay attempted to use the same tactic against Maje Culluh's Kazon raider, but Seska anticipated his plans and captured him. 

The Jem'Hadar used a type of antiproton beam to detect the USS Defiant (2370) through its Romulan cloaking device. The Cardassians later used this technique when the Defiant was hijacked by the Maquis in 2371. However, Thomas Riker, commanding the captured starship, was able to negate the beam by adjusting the resonance frequency of the cloaking device. 

A Federation starship could increase its shields by a factor of ten by taking the warp drive offline, remodulating its shields to emit a beta-tachyon pulse, and then emitting a series of focused antiproton beams to the shield bubble. According to B'Elanna Torres, though, this procedure entailed significant risk of the shield bubble igniting and "burning [them] all to a crisp". 

In an alternate timeline, Doctor Phlox developed a medical procedure using a focused antiproton beam to eliminate interspatial parasites in the brain of Jonathan Archer.