Plasma rifles are noted as type AI - burst weapons. However, they don't have an entry on p217, TW, burst fire weapon damage vs conventional infantry. I assume +2d6 from their description on page 140 applies to an attack on conventional infantry, but does the base 10 point attack do so or not?
One reading of the rules suggests that no, you just do one point, and since the table doesn't have plasma rifle on it, that's it. The footnote for non-infantry weapon damage against infantry for "heat-effect" weapons doesn't clarify particularly, since the PR is not a non-infantry weapon!