A proton-shield was a type of deflector shield. It was part of the defensive systems used on Golan Arms' DF.9 anti-infantry battery. The shield was generated by a proton shield generator from projectors located at the base of the tower and on the edge of the laser cannon turret.[1]
Sources
Star Wars Customizable Card Game — Hoth Limited Card: Golan Laser Battery (backup link)- The Essential Guide to Weapons and Technology